Arahan Teknik (Jalan) 13-87 - A Guide to the Design of Traffic Signal

Roads BranchPublic Works Department Malaysia

Jalan Sultan Salahuddin50582 Kuala Lumpur

Arahan Teknik (Jalan) 13/87

5.0m5.0m

7.0m7.0m

A Guide to

the Design of

Traffic Signals

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ARAHAN TEKNIK (JALAN) 13/87

JABATAN KERJA RAYA

CAWANGAN JALAN IBU PEJABAT J.K.R., JALAN SULTAN SALAHUDDIN50582 KUALA LUMPUR. HARGA : RM 12.00

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PREFACE

This Arahan Teknik (Jalan) on "A Guide to the Design of Traffic Signals" is to be used for thedesign of traffic signals at all intersections. It is to be used in conj unction with Arahan Teknik(Jalan) 11/87 s "A Guide to the Design of At - Grade intersections" and rather relevant ArahanTekniks.

This guideline presents fundamental concepts and practices related to traf fic signal design that areto be adopted. In the past, road engineers have been relying totally on the suppliers to come upwith signal timings and location design. With this gp;ideline, it is hoped that road engineers willnow be responsible for every aspcet of traf fic signal design instead of adopting the supplier'sdesign.

This Arahan Teknik vill be updated from time to time and in this respect, any feedback from userswill be most welcome. Any comments should be sent to Cawangan Jalan, lbu Pejabat JKR,Malaysia.

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CONTENTS

CHAPTER I INTRODUCTION

1.1 OBJECTIVES OF TRAFFIC SIGNAL CONTROL

1.2 ADVANTAGES AND DISADVANTAGES OF SIGNAL CONTROL

CHAPTER 2 SIGNAL INSTALLATION CRITERIA

2.1 GENERAL

2.2 WARRANT ANALYSIS

CHAPTER 3 SIGNAL OPERATION REQUIREMENTS

3.1 PHASING ELEMENTS

3.2 RIGHT-TURN PHASING

3.3 SUGGESTED GUIDELINES FOR SEPARATE RIGHT-TURN PHASES

3.4 SELECTION OF PRETIMED OR ACTUATION SIGNAL

CHAPTER 4 SIGNAL DISPLAY AND LOCATION

4.1 SIGNAL DISPLAY REQUIREMENTS

4.2 NUMBER AND LOCATION OF SIGNAL FACES

4.3 NUMBER OF LENSES PER SIGNAL FACE

4.4 SIGNAL SIZE, BACKPLATE, POSTAND ARRANGEMENT

4.5 EQUIPMENT AND MATERIAL

4.6 FLASHING OPERATION OF TRAFFIC SIGNALS

4.7 SIGNAL MOUNTING ALTERNATIVES

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CHAPTER 5 TRAFFIC SIGNAL CONTROLLERS AND DETECTORS

5.1 GENERAL

5.2 PRETIMED CONTROLLERS

5.3 ACTUATED CONTROLLERS

5.4 CONTROLLER LOCATION

5.5 DETECTORS

5.6 LOCATION OF DETECTORS

5.7 INSTALLATION CONSIDERATIONS

CHAPTER 6 TRAFFIC SIGNAL TIMING

6.1 OBJECTIVE

6.2 DESIGN PRINCIPLES

6.2.1 Determination of basic saturation flow, S

6.2.2 Determination of Y value

6.2.3 Determination of total lost time per cycle, L

6.2.4 Determination of optimum cycle time, Co

6.2.5 Determination of signal settings

6.2.6 Determination of Capacity

6.2.7 Determination of delays and queues

6.3 GUIDING PRINCIPLES

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CHAPTER 7 DESIGN OF PROGRESSIVE SIGNAL TIMING

7.1 ADVANTAGES

7.2 APPLICATIONS

7.3 PROGRESSIVE SIGNAL SYSTEM DESIGN

BIBLIOGRAPHY

GLOSSARY

APPENDIX A : DESIGN EXAMPLE

APPENDIX B : VEHICLE - ACTUATED SIGNAL FACILITIES

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LIST OF FIGURES

FIGURE PAGE

2-1 Peak hour volume warrant-urban or low speed

2-2 Peak hour volume warrant-rural or high speed

3-1 Two phase cycle

3-2 Three phase cycle

3-3 Four phase cycle

3-4 Heaviest right turn protected (leading green)

3-5 Heaviest right turn protected (lagging green)

3-6 Both right turns protected - no overlap (lead dual right)

3-7 Both right turns protected - no overlap (lag dual right)

3-8 Both right turns protected with overlap (quad right passing)

3-9 Lead lag

3-1.0 Directional separation

4-1 Cone of Vision for two lane approach

4-2 Typical arrangements of lenses in signal faces

4-3 Signal head configuration

4-4 Simple two--pole span

4-5 Bast arum with one overhead and one side mount signal head

6-1 Traffic Signal Calculations Reserve Capacity Diagram

7-1 Typical time space diagram

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LIST OF TABLES

TABLE PAGE

2-1 Vehicular Volume Requirements for Warrant 1

3-1 Comparison of Right-turn phase alternatives

4-1 Minimum Visibility distances

4-2 Adjustments for Grade Guidelines

5-1 Safe Stopping distance and detector setback

6-1 Relationship between effective lane width and saturation flow

6-2 Correction factor for the effect of gradient

6-3 Correction factor for the effect of turning radius

6-4 Correction factor for turning traffic

6-5 Conversion factors to P.C.U.'s

6-6 Tabulation of A = (I - X2)-----------2(1 - Xx)

6-7 Tabulation of B = X2----------2(1 - x)

6-8 Correction term of equation d = cA + B - K ---q

as a percentage of the first two terms

6-9 Level of Service for Signalised Intersection

6-10 Level of Service of Road

Page 8ARAHAN TEKNIK ( JALAN ) 13 / 87

1.1 OBJECTIVES OF TRAFFIC SIGNAL CONTROL

The overall objective of signal control is to provide for a safeand efficient traffic flow through intersections, along routes and in road networks. At individual intersections, the primary purpose is to assign right-of-way for alternate roads or road approaches in order to maximise capacity, minimise delay and reduce conflicts.

On a road system or network the overriding objective is to optimise the safety and effi-ciency of traffic flow on the system, which sometimes results in compromises at indi-vidual intersections.

1.2 ADVANTAGES AND DISADVANTAGES OF SIGNAL CONTROL

Traffic control signals,properlylocated and operated may provide one or more of the fol-lowing advantages:

(a) Provide orderly move-ment of traffic through an intersection.

(b) Minimise the number ofconflicting movements

(c) Increase the traffic handling capacity of theintersection.

(d) Provide a means of interrupting heavy traf-fic to allow other traffic to enter or cross.

(e) Can be coordinated to provide for nearly con-tinuous movement of traffic at a desired speed along a given route.

(f) Promote driver confi-dence by assigning right-of-way.

Traffic signal installation even though warranted by traffic conditions and properly or improperly located, designed, or operated, can produce the following d1sadvantages:-

(a) Increase total intersec-tion delay especially during off peak periods.

(b) Probable increase in certain types of acci-dents (rear end colli-sions)

(c) Can interrupt the pro-gressive flow of trafficon a route causing increased delay and stopping.

Chapter 1

INTRODUCTION

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INTRODUCTION

ARAHAN TEKNIK ( JALAN ) 13 / 87

(d) When improperly locat-ed causes unnecessarydelay and promote dis-respect for this type of control.

(e) When improperly timed,causes excessive delay, increasing driver irritation.

(f) In rural areas whore distinct peak hours traf-fic exist, serious acci-dents can occur during off-peak hours (eg. midnight) when some drivers on the major road may jump the red light.


2.1 GENERAL

A request. to install new trafficsignals (or upgrading an exist-ng signalised intersection) may originate from various sources. The most usual sources include :

(a) Responsible agencies ( e.g. JKR, City Hall, Municipalities etc. )

(b) Traffic : EnforcementAgencies ( e.g. Police )

(c) Industrial or commer-cial developers and operators

(d) Media/General Public

From whatever source the request may originate the responsible agency must determine whether such requests are justified. It is for this purpose that the followingcriteria of selection were developed. These criteria should be viewed as guide-lines, not as hard and fast val-ues. Satisfaction of a criteria does not : guarantee that the signal is really needed. Conversely, the fact that a cri-teria is not fully satisfied does not constitute absolute assur-ance that signalisation would not serve a useful purpose. Awareness of local conditions and sound engineering judge-ment would make the guidelines more effective.

In general the following steps should be taken prior to the installation of traffic signal control:-

(a) Determine the function of the intersection asit relates to the overall road system. A system of major roads should be designated to chan-nel major flow from onesection of the city to another. Intersection controls must be relat-ed to the major road system.

(b) A comprehensive studyof traffic data and phys-ical characteristics of the location is neces-sary to determine the need for signal control and for the proper design and operation ofthe control.

(c) Determine if the geo-metric or physical improvements or regu-lations will provide a better solution to the problem of safety or efficiency than the installation of signal control.

(d) Use establised war-rants to determine if intersection control is justified.

Chapter 2 : SIGNAL INSTALLATION CRITERIA

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SIGNAL INSTALLATION CRITERIA


2.2 WARRANT ANALYSIS

Generally the following war-rants should be considered before installing any signal control. They are namely :-

(1) Vehicular Operations

(2) Pedestrian Safety (S)

(3) Accident Experience

Traffic control signals should generally not be installed unless one or more of the warrants in this guideline are met.

Warrant 1 : Vehicular Operations

(a) Total Volume

Vehicular volume affects the efficiency and the Level of Service of an intersection.High traffic volume on the major road especially during peak hours, would invariably cause considerable delay for the traffic on the minor road . For the purpose of determin-ing the need for signal control,both the traffic volumes on themajor and minor roads shouldbe considered. A signal con-trol is warranted if the traffic volume for each of any 8 hourof an average day meets the minimum requirements in Table 2.1. For the major road, the total volume of both approaches is used.

For the minor road, the highervolume approach (one direc-tion only) is used.

An "average" day is defined as a weekday representing volumes normally and repeat-edly found at the location.

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(b) Peak Hour Volume

Peak hour volumes could alsohe used to determine the need for sigomliaation. This is applied in cases where, for one peak boor of an average day, traffic conditions are suchthat the minor road traffic experiences undue delay or hazard in entering or crossing the major road. This criteria warrants aigoaIioatiuo when the peak hour major road vol-ume (total vehicles per hour for both approaches) and the higher volume minor road approach (vehicles per hour for are direction only) fall

above the curve for a given combination of approach lanes shown in Figure 2.

The requirements are lower when the 85 percentilespeed of major roadtraffic exceeds 60 km/hr, or when the intersection lies within a rural area. The peak hour vol-ume warrant is satisfied when the volumes referred to fall above the curve for the given combination of approach lanes shown in Figure 2.2.

Table 2-l

Vehicular Volume Requirements for Warrant I

-------------------------------------------------------------------------------------------------------Number of Lanes Minimum Requirements (PCU)Each Approach ------------------------------------------------

Majur Road (1) Minor Road (2)-------------------------------------------------------------------------------------------------------Major Minor Urban Rural Urban RuralRoad Road-------------------------------------------------------------------------------------------------------1 1 500 350 150 105

2 or more 1 600 420 150 105

2 or more 2 or more 600 420 200 140

1 2 or more 500 350 200 140-------------------------------------------------------------------------------------------------------

(l) Total volume of both approaches(2) Higher volume approach only

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(c) Progressive Movements

In some locations., it may be desirable to install a signal to maintain a proper grouping or platooning of vehicles and regulate group speed even though the intersection. does not satisfy other warrants for signalisation. Several advan-tages may accrue from this type of consideration. Moving the traffic in platoons at the desirable speed would reducethe number of stops and delays. Accident reduction may also be expected with reduction of stops and speeds.

On a one-way road (or a road with predominantly unidirec-tional traffic), this warrant applies when the adjacent sig-nals are so far apart that they do not provide the necessary vehicle platooning and speed control. On a two--way road, the warrant is satisfied when the adjacent signals do not provide the necessary degree of platooning and speed con-trol and the proposed and adjacent signals could consti-tute a progressive signal sys-tem.

A signal installation under this warrant should be based on the 85-percentile speed unless a traffic engineering study indicates that another speed is more appropriate.

Warrant 2 : Pedestrian Safety

Signalisation of an intersec-tion also promotes pedestrian safety. It is warranted for sig-nalisation when, for each of any 8 hours of an average day the following traffic vol-ume exists :

(a) On the major road, 600or more vehicles per hour enter the intersec-tion (total of both approaches): or where there is a raised medi-an island 1.2 m or more in width, 1,000 or more vehicles per hour (total of both approach-es) enter the intersec-tion on the major road and

(b) During the same 8 hours as in paragraph (a) there are 150 or more pedestrians per hour on the highest vol-ume crosswalk cross-ing the major road.

When the 85-percentile speedof major road traffic exceeds 60 km/hr in either an urban or a rural area or when the inter-section lies within the built-up area of an isolated communityhaving a population of less than 10,000, the minimum pedestrian volume is 70 per-cent of the requirements above.

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A signal installed under this warrant at an isolated inter-section should be of the trafficactuated type with push but-tons for pedestrian crossing the main road. If such a sig-nal. is installed at an intersec-tion within a signal system, it should be equipped and oper-ated with control devices which provide proper coordi-nation.

Special considerations should be given at schools where large number of children crosses a major road on the way to and from school. The requirement for school chil-dren to cross is based on the number of adequate gaps available in the vehicular traf-fic on the major road avail-able. A signal may be installedto artificially create these gapsif other methods for improve-ments are not adequate.

Warrant 3 : Accident Experience

Accident prone areas with accident types which are cor-rectable by signal control war-rants signalisation. This claim should be substantiated by accident records for a period of two to three years. The requirements are satisfied when :

(a) An adequate trial of less restrictive reme-dies with satisfactory observance and enforcement has failed to reduce the accident frequency.

(b) There exist a record of five or more reportedaccidents in a year.These accidents shouldbe of types susceptible to correction by traffic signal control.

(c) There exist a volume ofvehicular and pedestri-an traffic not less than 80% of the require-ments specified in war-rants 1 and 2.

(d) The signal installation will not seriouslydisrupt progressive traf-fic flow.

Any traffic signal installed solely on this warrant should be semi traffic-actuated {with control devices which provide proper coordination if installedat an intersection within a coordinated system} and nor-mally should be fully traffic-actuated if installed at an iso-lated intersection.


After establishing that a signal iswarranted at a particular location, thenext major step involves determiningthe most appropriate method of con-trol. Decisions to be made at thislevel includes :

(a) Determining what are the phasing requirements

(b) Whether the signal should be pretimed or actuated.

3.1 PHASING ELEMENTS

Definitions :

(i) A signal phase = part ofthe cycle length allocat-ed to a traffic move-ment receiving the rightof way simultaneously during one or more intervals.

(ii) A traffic movement- a single vehicular move-ment, a single pedestri-an movement, or a combination of vehicu-lar and pedestrian movements.

(iii) Cycle length = the sum of all traffic phases.

There are a number of phas-ing options available. The sim-plest signal cycle is a two phase cycle, in which each road in turn receives a green indication while the cross-roadreceives a red indication. Aphasing diagram for a two-phase cycle is shown in Figure 3.1.

Three and four phase cycles are also quite common where there are heavy turning move-ments. The purpose of such multiphase cycle is to prevent traffic conflicts by giving heavyright-turn movements sepa-rate signal indications. Figures3.2 and 3.3 illustrates three and four-phase signal cycles.

Chapter 3

SIGNAL OPERATION REQUIREMENTS

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When right turning movements areheavy, protecting its movements arequite often essential to avoid unnec-essary conflicts. The basic:sequences which accomodate right-turn movements include :

(a) Heaviest right turn protected - This is a "lead right" in which the right-turning vehicles from only one approach are pro-tected and move on an arrow indication preceding the oppo-site through movement; or a "lag right" when the protected right turn follows the through movement phase. See Figures 3.4 and 3.5.

(b) Both right turn protected-no overlap. When the opposing right turns move simultane-ously followed by the through movements, it is termed "lead dual right". If the right turns follow the through movement it is called a "lag dual right". See Figures 3.6 and 3.7.

(c) Both right turns protected-withoverlap. In this operation, opposing right turns start simultaneously. When one ter-minates, the through move-ment in the same directions as the extending right. move-ment is started. When the extending right is terminated, the remaining through move-ment is started. When this type phasing is used on both roads, it is termed "quad right phasing". See Figure 3.8.

(d) Lead lag - This phasing is combined with a leading pro-tected right in one direction, followed by the through move-ments, followed by a lag right in the opposing direction. It is sometimes used in systems toprovide a wider two-way through band. See Figure 3.9.

(e) Directional separation - First one approach moves with all opposing traffic stopped, then the other approach moves with the first approach stopped. See Figure 3.10.

( The signal displays shown inFigures 3.4 to 3.10 are those visible to the starred ( * ) right turn movement ).

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Although there are no limita-tions on the numbers of phas-es that can be utilized, as a general rule they should be held to a minimum, especially in pretimed controllers. More than three phases tend to increase the cycle length and delay as they reduce the green time available to the other phases and intersection efficiency is impaired by start-ing delays, additional change intervals, longer cycles, and so forth. Multiphase actuated controllers when properly operated and timed tend to reduce these undesirable effects.

In determining the number of phases required at an inter-section, the goals of safety and capacity may conflict. For example, in many situations protected right-turn phases are safe for right--turning vehi-cles than permissive right turns. However, the added phases may result in longer cycle lengths, reduced progression in systems, and increased delay and percent of vehicles stopped. These factors adversely affect traffic performance, capacity, and fuel consumption, and may tend to reduce safety for all traffic.

3.2 RIGHT-TURN PHASING

In general the phasing issue is primarily a rightturn issue. When right-turning volumes and. opposing through vol-umes increases, a point is reached where right-turning traffic cannot find safe and adequate gaps. The provision of separate right-turn lanes will minimize the problem somewhat by providing stor-age space for those waiting for an acceptable gap in opposing traffic to turn. If the problem persists, the decision to provide separate right-turn phasing should be carefully weighed.

Two common right-turn phas-ing alternatives are the lead right and the lag right.

- Lead right : the protect-ed right turn precedes the accompanying through movement.

- lag right : the right turn phasing follows the through movement.

The most common practise is to allow opposing right turns to move simultaneously. This operation generally requires separate right-turn storage lanes.

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In actuated control, it is fre-quently desirable to split the right-turn phase so that when the demand on one right-turn phase ceases, the opposing through movement is released. This works very wellwith lead-right operations. In lag right, it is usually desirablefor the right turns to operate simultaneously. Both sequences have advantages and disadvantages as sum-marised in Table 3.1.

3.3 SUGGFSTED GUIDELINES FOR SEPARATE RIGHT-TURN PHASES

The following suggested guidelines may be applied when considering the addition of separate right-turn phasing for intersections having an exclusive rightturn lane.

(a) Volume

The product of right-turning vehicles and conflicting through vehi-cles during the peak hour is greater than 100,000 on a four-lane road or 50,000 on a two-lane road.

Right--turn volumes greater than 100 vehi-cles during the peak hour.

Right-turn peak period volumes greater than two vehicles per cycle per approach still wait-ing at the end of green.

(b) Delay

Minimum right-turn vol-umes of. greater than two per cycle during the peak period, and the average delay per right turning vehicle greater than 35 sec-onds.

(c) Accident experience

Four right-turn acci-dents in one year or sixin two years for one approach.

Six right-turn accidents in one year or ten in two years for both approaches.

(d) Geometrics

Two or more exclusive right-turn lanes are necessary.

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TABLE 3.1

Comparison of Right-Turn Phase Alternatives-------------------------------------------------------------------------------------------------------

Lead Right-Turn Phase-------------------------------------------------------------------------------------------------------Advantages Disadvantages-------------------------------------------------------------------------------------------------------Iucreamem intersection capacity Right turns may preempt theon one or two-lane approaches right of way from the oppos-without right-turn lanes when ing through movement whencompared with two-phase traffic the green is exhibited to thesignal operation. stopped opposing movement.

Minimizes conflicts between right-turn Opposing movements mayand opposing straight through make a false start in anvehicles by clearing the right-turn attempt to move with the vehicles through the intersection first. leading green vehicle

movement.

Drivers tend to react quicker thanwith lag right operations.

-------------------------------------------------------------------------------------------------------Lag-Right Turn Phase

-------------------------------------------------------------------------------------------------------Both directions of straight through Right-turning vehicles can be traffic start at the same time. trapped during the right-turn

yellow change interval asApproximates the normal driving the through traffic is notbehavior of vehicle operators stopping as expected.

Provides for vehicle/pedestrian Creates conflicts for opposingseparation as pedestrian usually right turns at start of lag startcrosses at the beginning of straight of lag interval as opposingthrough green. right-turn drivers expected

both movements to atom atthe same time.

Where pedestrian signals are used, Where there is no right turnpedestrians have cleared the inter- lane, an obstruction to thesection by the beginning of the lag through movement during thegreen interval. initial green interval is created

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-------------------------------------------------------------------------------------------------------Lag-Right Turn Phase

-------------------------------------------------------------------------------------------------------Cuts off only the platoon stragglers The hazards inherent in lag-from adjacent interconnected inter- right operations are such thatsection. they tend to restrict its use

to pretimed operations or to afew specific situations in actu-ated or control, such as "T'intersections.

A green arrow cannot bedisplayed during the circular yellow, there fore, a stop-startsitnation is necessary with simultaneously opposing rightturns.

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3.4 SELECTION OF PRETIMEDOR ACTUATION SIGNAL

3.4.1 Pretimed or Fix Timed Signal :-

This type of signal directs traf-fic to stop and permits it to proceed in accordance with a single, predetermined time schedule or a series of such schedules. The traffic signal isset to repeat a given sequence of signal indicationsregularly.

Advantages of Pretimed Signals.

(a) Simplicity of equipmentprovides relatively easyservicing and mainte-nance.

(b) Can be coordinated to provide continuous flowof traffic at a given speed along a particu-lar route, thus providingpositive speed control.

(c) Timing is easily adjust-ed in the field.

(d) Under certain condi-tions can be pro-grammed to handle peak conditions.

Disadvantages of Pretimed Signals.

(a) Do not recognize or accommodate short-term fluctuations in traf-fic demand.

(b) Can cause excessive delay to vehicles and pedestrians during. off-peak periods

3.4.2 Traffic Actuated Signals

The operation of this type of signal is varied in accordance with the demands of traffic as registered by the actuation of vehicle or pedestrian detec-tors as one or more approach-es.

Advantages of Traffic ActuatedSignals.

(a) Usually reduce delay (ifproperly timed)

(b) Adaptable to short-termfluctuations

(c) Usually increase capacity (by reappor-tioning green time).

(d) Provide continuous operation under low volume conditions as an added safety fea-ture, when pretimed signals should be put on flashing to prevent excessive delay.

(e) Especially effective at multiple phase intersec-tions

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Disadvantages of Traffic Actuated Signals

(a) The cost of an actuatedinstallations is two to five times the cost of a pretimed signal installa-tion.

(b) Actuated controllers and detectors are muchmore complicated than pretimed controllers, increasing maintenanceand inspection skill requirements and costs.

(c) Detectors are costly to install and require care-full inspection and maintenance to ensure proper operation.

3.4.3 Traffic-adjusted system

These are centrally controlled,as, for example, by a digital computer, and have settings which are updated from meas-urements of the system through detectors.

3.4.4 Comparison of Pre-timed and Traffic Actuated Control

With basic pre-timed control, aconsistent and regularly repeated sequence of signal indications is given to traffic. By use of attached auxiliary devices or remotely located supervisory equipment, the operation of pre-timed control

can be changed within certain limits to meet the require-ments of traffic more precisely.Pre-timed control is best suit-ed to intersections where traf-fic patterns are relatively sta-ble or where the variations in traffic flow that do occur can be accommodated by a pre-timed schedule without caus-ing unreasonable delay or congestion. Pre-timed control is particularly adaptable to intersections where it is desired to coordinate opera-tion of signals with existng or planned signal installations at nearby intersection on the same road or adjacent roads.

Traffic-actuated control differs basically from pre-timed con-trol in that signal indication are not of fixed length, but aredetermined by and confirmed within certain limits to the changing traffic flow as regis-tered by various forms of vehi-cle and pedestrian detectors. The length of cycle and the sequence of intervals,may vary from cycle to cycle, depending on the type of con-troller and auxiliary equipmentutilized to fit the needs of the intersection. In some cases, certain intervals may be omit-ted when there is no actuationor demand from waiting vehi-cles or pedestrians.


To serve its intended purpose indirecting and regulating traffic flow,two fundamental principles must becarefully considered, i.e. conspicuityand clarity. Conspicuity means thatthe signal must not only be visible,but must be obvious to the eye andattract attention. Clarity means thatthe message or direction given canbe easily understood. In other words,the signal must be seen in order forthe driver to react and the requiredaction must be obvious.

4.1 SIGNAL DISPLAYREQUIREMENTS

For the driver to respond effectively to the traffic signal, these basic requirements has to be considered.

The amount of light reaching the driver's eye.

The position of the sig-nal in the driver's field of view.

The ratio of the signal-to-background contrast.

The amount of compet-ing information sources(visual clutter or "noise")

The degree to which the appearance -of the signal is expected.

The degree to which the precise location of the signal is known.

The degree to which the message conform to the driver's knowl-edge and expectations.

The physical details of these elements that ,feet the driver'sability to see and respond to message transmitted are pro-vided below:

Minimum Visibility Requirements :

Minimum visibility for a traffic signal is defined as the dis-tance from the stop line at which a signal should be con-tinuously visible for various approach speeds.

Table 4.1 shows, for example,that if the 85percentile approach speed is 56 kph the signal faces should be visible from a distance of 99 m. And they should be continuously visible from that point all the way to the stop line at the intersection.

CHAPTER 4

SIGNAL DISPLAY AND LOCATION

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As these distances do not consider the impact of grade, it may be necessary to adjust the minimum visibility dis-tances to reflect an upgrade or downgrade approach. Table4.2 can be used for this pur-pose.

If the signal faces are not visi-ble from the distance specifiedby the chart, signs WD.22 andWD.17 must be installed to warn drivers. (Please refer to "Arahan Teknik (Jalan) 2A/85 -Manual on Traffic Control Devices : Standard Traffic Signs" for the details of the signs)

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Table 4.1

Minimum Visibility Distances

Table 4.2

Adjustments for Grade Guidelines

85 percentile speed,kph

Minumum VisibilityDistance, m

Desirable Distance, m

324048566472808897

53668299119140165190218

8199123146174201232265299

85 percentile speed, kph Add for Downgrade, m Subtract for Upgrade, m

5% 10% 5% 10%

324048566472808897

2356912151821

569142027374658

233569111417

35681115202429

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4.2 NUMBER AND LOCATION OF SIGNAL FACES

It is advisable that there be at least two signal indications foreach through approach to an intersection or other sig-nalised location. A single indi-cation is permitted for control of an exclusive turn lane pro-vided that this single indica-tion is in addition to the mini-mum two for through move-ment lanes.

Supplemental signal indica-tions are recommended if theiruse will improve what would otherwise be marginal visibilityor detectability of the signal indication. Additional heads used for this purpose should be located as close as possi-ble to the driver's projected line of sight. Typical situations where supplemental indica-tions may materially improvevisibility include :

Approach widths in excess of three full lanes and very wide intersecting road.

Driver uncertainty con-cerning the proper location at which to stop.

High percentages of large trucks in the traf-fic stream that tend to block the view of signalindications in their nor-mal location.

Approach alignment that makes continuous visibility of normally positioned signals impossible.

The placement of the signal face depends on the visibility requirements for a specific location. Generally, the pre-cise location should consider the lateral and vertical angles of sight toward the signal as determined by (1) typical driv-er eye position; (2) vehicle design; and (3) the vertical, longitudinal, and lateral posi-tion of the signal face. The first two factors are relatively consistent. It is the third factorthat varies as a function of theintersection geometry. Accordingly, the optimum physical layout of the individ-ual intersection must be care-fully designed to assure that the signal indication lies withinthe driver's cone of vision.

4.2.1 Cone of Vision

Vertically, a driver's vision is limited by the top of the vehi-cle's windscreen. This restric-tion requires that the signal belocated far enough beyond thestop bar to be seen by the driver of a stopped vehicle. The lateral location of the faceis based on the driver's cone of vision and the width of the intersecting cross roads.

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It has been determined by recognized human factor stud-ies that generally a driver's lateral vision is excellent up to5 on either side of the center line of the eye position (a cone of 10 ). Vision is still verygood up to 10 on either side (cone of 20 ). At 20 on either side (cone of 40 ), the driver's vision is judged as "ade-quate". Therefore it requires that at least one (and prefer-ably two) signal faces be located within a cone 20 to the left or 20 to the right of the"center of the approach lanes extended." This constitutes the maximum acceptable cone.

The cone of vision originates at a point which represents the center of the approach lanes at the stop line. Parking lane is usually excluded and separate turn lanes are includ-ed unless they are controlled by separate signal displays.

This concept is illustrated in Figure 4.1. The maximum cone of vision in this figure is shown superimposed on a typical two-lane approach.

4.2.2 Lateral Clearance

On roadways whose edges are defined by a raised kerb, the poles shall be erected so that no part of the signal headother than overhead signals project over the roadway. If possible the signal housing should have a clearance of a minimum 450 mm from the kerb line.

4.2.3 Height of Signal Faces

The bottom of the housing of a signal face, not mounted over a roadway, shall not be less than 2.0 m nor more than3.5 m above the sidewalk or, ifnone, above the pavement surface at the center of the roadway. The bottom of the housing of a signal face sus-pended over a roadway shall not be less than 5.5 m nor more than 8.5 m above the pavement surface at the cen-ter of the roadway.

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4.2.4 Other Locational Criteria :

a) Where a signal face is meant to control a spe-cific lane or lanes of approach, its position should be unmistakablyin line with the path of that movement.

b) Where possible, signal displays which control through traffic must be located within a maxi-mum of 35 metres beyond the stopline.

c) Where the secondary signal face is more than 35 m and less than 45 m beyond the stop line, a supplemen-tal near-side signal indi-cations is required.

4.3 NUMBER OF LENSES PERSIGNAL FACE

Each signal face, except in pedestrian signals, shall have at least three lenses, but not more than six. The lenses shall be red, yellow or green in color, and shall be given a circular or arrow type of indi-cation. Allowably exception to the above is were a single section green arrow lens is used alone to indicate a con-tinuous movement.

4.4 SIGNAL SIZE, BACK-PLATE, POST AND ARRANGEMENT

a. For uniformity, only onestandard size of signal indication is used i.e. the 300 mm lens. This 300 mm lens yields a maximum center lumi-nance two or more times higher than the maximum center lumi-nance of 210 mm indi-cations. In addition, thislarger size lens increases light output and provides better vis-ibility.

b. All these signal indica-tions must be mounted on a black backplate with an orange colored border.

c. The post must be col-ored in black and orange strips with a 0.3m interval (See Arahan Teknik Jalan 2B/85 - Traffic Sign Applications)

d. Visors should be used in all installations.

e. For typical arrange-ments, see Figure 4.2.

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4.5 EQUIPMENT AND MATERIAL

All equipments and materials must conform to BS 505 "Specification for Road Traffic Signals". The color of the lighttransmitted by the signals shall comply with the limits setout in British Standard 1376.

4.6 FLASHING OPERATION OFTRAFFIC SIGNALS

All traffic signal installations shall be provided with an elec-trical flashing mechanism. Amanual switch, or where appropriate, automatic means shall be provided to operate this.

The illuminating element in a flashing signal shall be flashed continuously at a rate of not less than 76 nor more than 84 times per minute. Theilluminated period of each flash shall be not less than half and not more than two-thirds of the total flash cycle.

When traffic control signals are put on flashing operation, the following meanings imply,

(a) The system breaks down or

(b) Low-traffic period con-trol (usually after mid-night)

Automatic changes from flash-ing to stop-and-go operation shall be made at the begin-ning of the major road green interval, preferably at the beginning of the common major road green interval, (i.e., when a green indication is shown in both direction on the major road). Automatic changes from stop-and-go to flashing operation shall be made at Lhe end of the com-mon major road red interval, (i.e., when a red indication is shownboth directions on the major road).

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Where there is no common major road green interval, theautomatic change from flash-ing to stop-and-go operation shall be made at the begin-ning of the green interval for the major traffic movement on the major road. It may be nec-essary to provide a short, steady all red interval for the other approaches before changing from flashing yellow to green on the major approach.

4.7 SIGNAL MOUNTING ALTERNATIVES

There are three basic ways that signal indication may be mounted :

1. post or pole mounted

2. span-wire mounted

3. mast-arm mounted

The type of mounting used depends to some extend on local practice, aesthetic appearance and cost.

4.7.1 Post-or pole mounted signals The term post-mounted sig-nals usually refers to signal head assemblies mounted on their own - 100 mm to 150 mm dia. metal post. Signals may also be mounted on poles used for other purposes(eg. lighting poles or tele-phone).

All post or pole mounted sig-nals must be installed 2.0 m to 3.5 m above the sidewalk or pavement surface at the centre of the highway if no sidewalks exist. Typical post mounted signal installations are shown in Figure 4.3.

Advantages-of Post-Mounted Signals are :-

Low installation costs

Easy maintenance, no roadway interference

Generally considered as most aesthetically acceptable.

Generally good loca-tions for pedestrian sig-nals and push buttons.

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Where wide medians with right-turn lanes and phasing exist, pro-vide good visibility.

Disadvantages are :

Requires underground wiring which may offsetinitial cost advantages

May not provide loca-tions which meet mini-mum conspicuity

Generally does not pro-vide good conspicuity.

May not provide mount-ing locations such that a display with clear meaning is provided.

Height limitations may provide problems where approach is on avertical curve.

4.7.2 Span-wire mounted signals :

In a span-wire installation, all or most of the traffic signal faces are mounted overhead. In this application, strain polesare installed at two or more locations at the intersection, amessenger (or support) cable is strung between the poles, and signal heads are attachedalong the messenger. Wiring is run overhead.along themessenger cable to the signalheads. Figure 4.4 illustrates a simple span wire mounted sig-nals.

Advantages of two-pole sim-ple span

Low installation-costs.

Allows good lateral placement of signals for maximum conspicu-ity.

Minimum number of poles to clutter side-walk area

Easy to install, little or no underground work required.

May be combine'd with utility poles.

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Disadvantages of two-pole simple span

Poor visibility from stopline at intersections of narrow streets.

May result in very long spans.

All heads are located on one span maximiz-ing loading on cable and poles.

Often considered unpleasing aesthetical-ly because of head "clutter".

Poor pedestrian visibili-ty of indications.

No provision for servingall corners with pedes-trian push buttons.

4.7.3 Mast-Arm Mounted Signals

Mast-arm mounting is a can-tilevered structure which per-mits the overhead installation of the signal faces without overhead messenger cables and signal wiring. The cable connecting the signal heads tothe controller is run inside the pipe and arm structure. The mast-arm mounting can be effectively combined with pole-mounted signals. Example of mast-arm installa-tions is given in Fig. 4.5.

Advantages of Mast-Arm

Allows excellent lateral placement

Provides good con-spicuity from stop-line

May provide side-mount locations for supplementary signals or pedestrian faces andpush buttons.

Generally accepted as an aesthetically pleas-ing overhead mounting.

Rigid mountings pro-vide positive control of signal movement in wind.

Disadvantages of Mast-Arm

Costs are higher than other mounting alterna-tives

On very wide approaches it may be difficult to properly place signal faces over the lanes they control.


The designer should decide on thetypes of control he/she wants in thetraffic system. The types of signalsystem controls have been dis-cussed in Chapter 3. In the case ofvehicle actuation control, the design-er has to further decide on the typeand location of the vehicle detectorsrequired. It is proposed that all signalinstallations should be of the vehicleactuated control type.

5.1 GENERAL

Traffic signal controller can beclassified into either pretimed or actuated. Semi-actuated, full actuated, and volume-den-sity modes can be provided within the current state-of-the art basic actuated controller unit.

5.2 PRETIMED CONTROLLERS

This common type of con-troller operates according to apredetermined cycle lengths and phase intervals. It is fre-quently used when there are predictable and stable traffic volumes. It provides a simple, economical means of traffic control, and because of its simplicity, it is very reliable and relatively easy to main-tain. Because pretimed controldoes not recognise or

accommodate short-term fluc-tuations in traffic demand, it can cause excessive delay to vehicles and pedestrians where there exists a high degree of variability in the traf-fic flows.

5.2.1 Timing Characteristic :

Pretimed controllers has the following characteristics from a timing standpoint :

(a) Provide a fixed amountof time for each phase interval

(b) Each phase or move-ment can be divided into a number of dis-cretely timed interval such as phase green, flashing walk, yellow change and all red clearance. The same timing is provided for each of these intervals regardless of demand.

Pretimed controllers do have a degree of flexibility in vary-ing timing. Changes in timing can be accomplished to pro-vide different, cycle lengths, interval timing, and/or offset. Timing plans are usually selected on a time-of-day/dayof-week basis by means of time clocks.

Chapter 5

TRAFFIC SIGNAL CONTROLLERS AND DETECTORS

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5.3 ACTUATED CONTROLLERS

A traffic-actuated controller operates with variable vehicu-lar and pedestrian timing and phasing intervals which depend on traffic volumes or the presence of pedestrians. The flows are determined by vehicular detectors placed in the roadway or by pedestrian actuation of push buttons. Thebasic applications of actuated control include semi-actuated,full-actuated, and volume den-sity.

5.3.1 SEMI-ACTUATED CONTROLLERS

These devices provide the mean for traffic actuation on one or more, but not all of the intersection approaches. It is applicable primarily to an intersection of a heavy - vol-ume, urban or suburban trafficarterial with a relatively lightly travelled minor road. The essential operating features ofthe controller are :

a) Detectors are on minor approaches only.

b) Major, road receives a minimum green period in each cycle.

c) Major road receives green indefinitely after minimum period, until interrupted by the minor phase detector, actuation.

d) Minor phase receives green after actuation provided major phase has completed mini-mum green period.

e) Minor phase receives minimum initial green period.

f) Minor phase green is extended by additional actuations until preset maximum limit is reached or a gap in actuations greater than the unit extensions occur.

g) Additional actuation willbe remembered if max-imum has been reached on minor phase and will return green after major phase interval.

h) Yellow change and all-red clearance intervals are preset for each phase.

This kind of control is excel-lent for use where a light side-road volume cannot safely cross major flows without sig-nalisation. If sideroad flows are sporadic, the regular inter-ruption of the major flow with pre-timed control cannot be justified. Where both road vol-umes fluctuate widely, semi-actuated control should not beused, since there are no detectors on one or more legs.

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5.3.2 Full - Actuated Controllers

This provides for actuation by vehicles on all legs of the intersection. It is applicable primarily to an isolated inter-section of roads that carry approximately equal traffic vol-umes, but. where distribution between approaches varies and fluctuates. It then becomes necessary to take into consideration the demands on all approaches. The essential operating fea-tures of the controller are :

a) Detectors on all approaches

b) Each phase has preset initial interval to providestarting time for stand-ing vehicles.

c) Green interval is extended by a preset unit extension for each actuation after the initialinterval expires, provid-ed a gap greater than the unit extension doesnot occur.

d) Green extension is lim-ited by a preset. maxi-mum limit (some equip-ment can provide two maximums per phase).

e) Yellow change and all-red clearance intervals are preset for each phase.

f) Each phase has a recall switch

- when both recallswitches are off the green will remain on one phase when no demand is indi-cated on the other phase.

- when one recall switch is on, the green will revert to that phase at every opportuni-ty.

- when both recallswitches are on, the controller willcycle on a fixed-time basis in the absence of demand on either phase (oreinitial interval and one vehicle interval on each phase).

Because of their actuated nature, full-actuated con-trollers cannot be coordinated with other signals without los-ing the flexibility for which they were designed. Demand patterns for which they are applicable, as well as the inability to coordinate make the requirements of isolated locations (about 2 km between adjacent signals) a fairly strong one.

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5.3.3 Volume - Density Controllers

This class of device offers additional responsiveness in signalisation for isolated inter-sections. Green time is allot-ted on the basis of volumes on approach legs. Unlike sim-ple actuated signal, the vol-ume-density signals does not merely react in a predeter-mined fashion to an actuation,but is able to record and retain information regarding volume, queue length, and delay times. In addition, a phase will lose the green by any one of three mechanism.

a) There are no vehicles producing any further demand on the approach.

b) The maximum green phase is reached.

c) The time gap between vehicles on the approach exceeds the maximum standard.

The last mechanism is the "density" function of the sig-nal. At the beginning of a green phase, the maximum time gap might be, for exam-ple, 5 seconds. As the green phase continues, the maxi-mum time gap decreases. Thephase is lost when the maxi-mum gap is exceeded, or when the maximum length of phase is reached, whichevercomes first. This type of con-trol provides the greatest

flexibility in traffic-actuated controllers, in that it is capableof taking into consideration the number of vehicles waitingon an approach, as well as the volume on the approach with the green indication. Its use is primarily applicable to an isolated intersection with wide traffic fluctuations between roads. The essential operating features of the con-troller are :

a) Detectors on all approaches

b) Each volume density phase has an initial green time that, can bevaried by :

- added initial,

- computed initial, or

- extensible initial,

c) Passage time is the extended green time created by each addi-tional actuation after the initial green time has elapsed. This time is set as that required to travel from the detector to the stop line.

d) Passage time is reduced to a minimum gap after a preset time.

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e) Maximum green or extension limits are preset for each phase.

f) Yellow change and all-red clearance intervals are preset for each phase.

5.4 CONTROLLER LOCATION

The signal controller may be attached to any convenient pole or, if a console cabinet is used, it may be placed wher-ever desired, provided that ,in either case the location cho-sen satisfies the following :-

(a) A power supply can be conveniently obtained.

(b) There will be an unob-structed view of all approaches to the intersecton in the eventof manual operation. When this condition cannot be satisfied andmanual operation is fre-quently required, it maybe desirable to install a special remote unit at amore favourable posi-tion with its switches in parallel with those of the controller proper.

(c) The cabinet does not unduly obstruct the pedestrian right of way.

(d) The cabinet will not be unduly exposed to acci-dental damage caused by passing traffic.

5.5 DETECTORS

Traffic detectors are a primaryrequisite of actuated signal controls as they sense vehicu-lar or pedestrian demand and relay these data to the local intersection controller or mas-ter controller so that the appropriate signal indications may be displayed. The selec-tion of the type, design, and installation of the various types of detectors is a func-tion of the operational require-ments and physical layout of the area to be detectorised.The functional characteristics of the most commonly used detectors are described below.

5.5.1 Types and Functions of Vehicular Detectors

The type of vehicle detection system used for an actuated signal control depends on the operational requirements of the intersection in terms of thetype and use of data needed by the controller to operate efficieVtly. Most. new installa-tions use either inductive loop detectors, magnetic detectors,or magnetometers. The physi-cal design and construction ofthese commonly used detectors is summarized below:

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(a) Inductive Loop Detectors : Loop detec-tors are by far the mostcommonly used today and are the standard form of detection in many agencies. Essentially, this detec-tor installation consists of a loop which may beone or more turns of wire in a saw-cut slot inthe road surface in the exact area where vehi-cles are to be detected.The ends of this loop are connected by cableto an electronic amplifi-er usually located in thecontroller. A vehicle passing over, or restingin the loop, will unbal-ance a tuned circuit which is sensed by the amplifier.

(b) Magnetic Detectors :There are three types of magnetic detectors :-the standard magnetic detector, a directional magnetic detector, and the magnetometer. All three types consist of two components, an in-road sensor, and an amplifier unit. Although all 3taagnetic detectors operate on the basis of a change in the lines offlux from the earth's magnetic field, the magnetometer is a spe-cial type of magnetic detector.

The directional and nondirec-tional magnetic detector uti-lizes a coil of wire with a high-ly permeable core placed beneath the surface of the roadway. When a vehicle comes near or passes over the coil, the constant lines of flux passing through the coil are deflected causing a volt-age to by developed in the coil. A high--gain amplifier causes the voltage to operate a relay and transmit to the controller the message that a vehicle has been detected. For these detectors to sense a change in the magnetic field, the vehicle must be in motion. Vehicles travelling less than 10 kmph are gener-ally not detected. Consequently, magnetic detectors can provide the equivalent of passage or motion data, but not occupan-cy or presence data.

(c) Other Types of Detectors

Earlier detectors that have been use overseas include pressure pads, radar, and sonic detectors. Their use is now very limited.

The pressure detector requires a metal frame installed in the pavement to support and hold in place a pressure plate. The detector isactivated by the weight of a vehicle causing a closure of contact plates sealed in the rubber pressure plate which

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sends a signal to the con-troller. This detector is no more in use.

Radar detectors operate on the Doppler effect. Microwaves are beamed toward the roadway by a transmitter. A vehicle passing through this beam reflects the microwaves back to the antenna denoting the motion of a vehicle.

The sonic detector also uses the Doppler principle. it trans-mits pulses of ultrasonic ener-gy toward the roadway through a transducer. A vehi-cle passing through thisreflects the energy at a differ-ent frequency back to the transducer which denotes a presence or passage of a vehicle. These detectors are of special value, when it is notpossible or practical to install loops, magnetic, or magne-tometer detectors (e.g., on bridges or approaches with poor base materials).

The high-intensity light detec-tor is a special purpose detec-tor system used for priority control for emergency and transit vehicles. It utilizes a high-intensity light emitted at aspecific frequency from a transmitter mounted on the vehicle and a detector mount-ed on or near the traffic sig-nal. When the light from an emergency or priority vehicle is detected, the detector relays a signal to a phase

selector connected to the con-troller. However, this type of detector has never been usedin this country.

5.5.2 Application of Vehicle Detectors

The application and design of the detection component of actuated traffic signal contol isexplicitly related to controller operation which in turn is related to the physical and traffic characteristics of the location.

There are a number of ways in which detector application and design can be approached. Detector locationand configuration is depend-ent on

a) Type and capability of controller

b) Control mode

c) Traffic variable to be measured

d) Geometry of the inter-section and approach-es

e) Traffic flow characteris-tics (e.g., volume, speed, etc.)

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Short loop detectors (up to 6 meter in length) constitutes the simplest and most widely used type of detector applica-tion. This short loop (small area) configuration is intendedto detect a vehicle upstream of the stop' bar. When a vehi-cle passes over the detector, a "call" is placed and the con-troller responds as pro-grammed.

Short loop detectors may takea number of forms and be located at varying distances upstream of the stop bar depending on the operational requirements. A common application is to space the detector loop about 30m upstream of the stop bar. However this may vary in practise depending on the approaching vehicular speed.

Long loop detection can also be used and it is essentially a presence detection in that it registers the presence of a vehicle in the zone of detec-tion as long as the detector is occupied. This method is expensive but multiple small loops could be used to over-come this problem.

5.5.3 Detection of Small Vehicles

A presence detector should beable to detect all licensed motor vehicles including a small motorcycle and hold its call until the display of a greento the phase. A hold time of 3

minutes is commonly speci-fied. A conventional detection loop configuration longer than 6 meter may not detect a small motorcycle.

5.6 LOCATION OF DETECTORS

Ideally, the detector location should consider the speed, type, and volume of approach-ing vehicles as well as the type of controller unit. Table 5.1 presents a range of suggested detector setbacks. The values are determined asa function of deceleration rata,reaction time, and decelera-tion distance.

The detector requirements for low-speed approaches differ from the requirements associ-ated with high-speed approaches. Modern controllerunits are able to detect and register the number of vehi-cles that. have passed over the detector. With this capabil-ity, it is sufficient for a low-speed approach or an urban condition approach to install just one detector. This detec-tor should be placed about 30m upstream of the stop bar.Adjustments to the variable Initial Green Time can accom-modate the traffic built up at the stop bar during the red period. This facility is availablein present controller units.

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Table 5. 1

Safe Stopping Distance and

Detector Setback

-------------------------------------------------------------------------------------------------------Deceleration rate, d = 3.28 m/s

Deceleration time, t = V/d, seconds

Speed, V = m/o

Reaction time, r = I second

Reaction Distance, 8 = r s V metre

Deceleration distance, D = l/2 Vt metre

Safe stopping distance, S = B + D metre= r u V + l/2 Vt

-------------------------------------------------------------------------------------------------------

* Use multiple detectors

Speed( km/h )

V( m/s )

Decel.Time, t( secs )

Reac.Dist, R

( metre )

Decel.Dist, D

( metre )

TotalDist, S

( metre )

DetectorSetback( metre )

24324048566472808896105

6.78.911.213.415.617.920.122.324.626.829.0

2.202.933.674.405.135.876.607.338.078.809.53

6.78.911.213.415.617.920.122.324.626.829.0

7.413.120.529.540.152.566.481.999.2118.0138.4

14.122.031.842.955.770.486.5104.2123.8144.8167.5

142232435670*****

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5.7 INSTALLATION CONSIDERATIONS

To operate effectively, detec-tors must be properly designed and carefully installed. An improperly installed detector can serious-ly degrade the efficient opera-tion of the controller ' or even render the controller inopera-tive.

Essentially, the inductive loop detector wire is normally a l3-or 14-gauge conductor embedded in a saw-cut slot approximately 75 mm below the pavement. A sealant, suchas asphalt, epoxy, polyurethane, or polyester compounds, is used to seal the loop in the pavement. An alternate, more durable con-struction is to place the turns of wire in a plastic conduit within or just below the pave-ment surface or within a plas-tic sleeve laid in the, saw-cut in the pavement. This method is preferred.

The width of the loop is nor-mally 1.8 meter while the length can range from 1.8 meter to 30 meter. The effec-tive area of detection normallyextends about 0.76 m outside the loop.

Very large loops of up to 9 meter in width and 16 to 1-8 meter feat in length can pro-vide an extension of green time when occupancy increas-es to a saturation point in a given direction.


CHAPTER 6

TRAFFIC SIGNAL TIMING

6.1 OBJECTIVE

The objective of signal timing is to alternately assign the right-of-way to various traffic movements (phases)in such a manner as to minimizeaverage delay to any single group of vehicles or pedestrians and to reduce the probability of accident producing conflicts.

6.2 DESIGN PRINCIPLES

6.2.1 Determination of saturation flow, S

The capacity of a traffic-signal controlled intersection is limited by the capacities of the individual approaches to the intersection. This capac-ity of an approach is measured independently of traffic and other controlling factors and is expressed as the saturation flow.

Saturation flow is defined as the maximum flow, expressed as equiva-lent passenger cars, that can cross the stop line of the approach where there is a continuous green signal indication and a continuous queue of vehicles on the approach.

Basic saturation flow (S) expressed in passenger car units per hour with no parked vehicles is given by

i) where effective approach width W > 5.5 m

S = 525 W p.c.u./hr

ii) and where W < 5,5 m, see Table 6-1.

Where there are parked vehicles, effective approach width is to be reduced by LW where

LW = 14 - 0.9 ( Z-7.6 ) / k

Where Z (>7.6 m) is the clear distance of the nearest parked car from the stop line (m) and k is the green time (sees).

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If the whole expression becomes negative, the effective lose should be taken as zero. The affective loss should be increased by 50 percent for a parked lorry or wide van.

Note : The British formula, assuming m green time of 30 seconds, infers thatthere is no effect on the approach capacity if parking is approximately 61 m (20O ft) or more away from the stop line.

This basic saturation flow is then has to be corrected for the effect of gradient, turming radium, and the proportion of turning traffic.

Table 6-l

Relationship between effective lane width and saturation flow

a) Gradient

See table below

w ( m ) 3.0 3.25 3.5 3.75 4.0 4.25 4.5 4.75 5.0 5.25

s( pcu/h )

1845 1860 1885 1915 1965 2075 2210 2375 2560 2760

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Table 6-2

Correction factor for the effect of gradient

b) Turning radium

Saturation flows for approaches with exclusive turning traffic need to be corrected with factor that takes into consideration the magnitude of the turning radius, R. See table below.

Table 6-3

Correction Factor for the effect of turning radius

Correction Factor, Fg Description

0.850.880.910.940.971.001.031.061.091.121.15

for upward slope of 5%for upward slope of 4%for upward slope of 3%for upward slope of 2%for upward slope of 1%

for level gradefor downward slope of 1%for downward slope of 2%for downward slope of 3%for downward slope of 4%for downward slope of 5%

Correction Factor, Ft Description

0.850.900.96

for turning radius R < 10 mfor turning radius where 10 m < R < 15 mfor turning radius where 15 m < R < 30 m

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c) Turning traffic

When u lane comprises straight-on and turning traffic, the pro-portion of turning traffic is one of the factors determining the saturation flow, S.

Table 6-4 specifies correction factors for various percentages ofturning traffic over the total traffic on the approach lane.

Table 6-4

Correction factors for turning traffic

Note :

1. If a lane comprises both right and left turning traffic, the total factor will be Fr x Fl

2. In cases where total saturation flow of the exits is lower than of the approaches, the lower value has to be taken into account.

% turning traffic Factor for right-turn,Fr

Factor for left-turn,F1

51015202530354045505560

0.960.930.900.870.840.820.790.770.750.730.710.69

1.001.000.990.980.970.950.940.930.920.910.900.89

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6.2.2 Determination of Y value

Y = q/S

where y = ratio of flow to saturation flow

q = actual flow on a traffic-signal approach converted in pcu/hr ( See Table 6-5 for conversion )

S = saturation flow for the approach in pcu/hr.

The y value for a phase is the highest y value from the approaches within that phase.

nFor the whole junction, Y = E yi

where n = number of phase

yi = highest y value from the approach within that phase i.

This Y value is a measure for the accupancy of the intersection. Y should preferably not be higher than 0.65. If the value found is higher than 0.85, it is recommended that the geometrics of the inter-section be upgraded to increase the capacity.

Table 6-5

Conversion factors to pcu's

Vehicle Type Equipment pcu value

Passenger carsMotor cyclesLight vans

Medium lorriesHeavy lorries

Buses

1.000.331.751.752.252.25

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6.2.3 Determination of total lost time percycle, L

From Webster and Cobbe, the total lost time per cycle is

n nL = E ( I - a ) + E1

I=1 I=1

where I = the intergreen time between the phases a the amber time, usually taken as 3 seconds.

a = the amber time, usually taken as 3 seconds.

1 = drivers reaction time at begin of green per phase. In practise, this time is set to 2 seconds but 0 - 7 seconds can also be used.

Note :

i ) The shortest total lost time is the most economic one because the greater part of the cycle can be used by traffic flows.

ii ) Intergreen, I = R + a (in seconds) where R = all red interval

iii ) To check for adequacy of amber time, a

a = V + W + L----- ---------2 A V

where

a = amber time ( sec )2

A = acceleration ( taken as 4.58 m/S )

V = approach speed ( m/s )

W = width of intersection crossed ( m )

L = length of vehicle ( suggested 5.5 m )

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6.2.4 Determination of optimum cycle time, Co

An expression for the optimum cycle time, Co,is given in Road Research Technical Paper No. 56 as

Co = 1.5L + 5 ( in seconds )------------

I - Y

This optimum cycle time, Co, gives the minimum average delay for theintersection. But this delay is not greatly increased if the cycle time varies within the range of 0.75 to 1.50 of the calculated Co.

For practical purposes, cycle time should be between 45 seconds to 120 seconds, although an absolute minimum of 25 seconds can be used.

8.2.5 Determination of signal settings

Effective green time is the green time plus the change interval minus the lost time for a designated phase.

The total effective green time = cycle time minus total lost time.

g + g + ........... + g = Co - L1 2 n

where n denotes the number of phases and gn is the effective green time of phase n.

For optimum conditions

g = y ( for a 2 phase cycle )1 1

-- --g y2 2

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With the above ratio, the following formulas apply to each individual phase.

g = Yn (Co - L) ( in seconds )n ----

Y

where g = effective green time of the nn signal phase

Yn = calculated Y-value of the same signal phase.

For a 2 phase cycle

9 = Yl ( Co L ) 1 ---

Y

and g = Y (Co L) 2 2

---Y

The actual green time, G = 9 + I + R

The controller setting time, K = G - a - R= g + 1 - a

Therefore for a two-phase example

K = g + 1 - a1 1

and K = g + I - a2 2

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6.2.6 Determination of Capacity

a) Practical capacity, Y prac

The maximum possible value of Y which can be accommodat-ed is

Y max = 1 - L-----CM

where L = total lost time ( sec )

C = maximum cycle time (sec) m

*For practical purposes, Cm = 120 seconds

than Y = 0.9 - 0.0075 Lprac

For design purposes Co is used rather than Cm.

b) Reserve Capacity, RC

This reserve capacity is the difference between the capacity and the actual flow. As a percentage of the present flow, RC is given by

RC = 0.9 ( 1 - L/C max ) - Y x 100%-----------------------------

Y

or more conveniently

RC = Y - Yprac

-------------------- x 100% Y

Y is the actual value at the junction.

A useful mean of calculating RC is by using the Reserve Capacity Diagram in Figure 6-1

Page 63



c) Design Life of Junction, n

n = log ( Q1 /Qo )------------------log ( I + GR )

where n = number of years

Q1 = 90% of ultimate capacity

Q0 = present flow

MGR = growth rate

This design life is calculated when C = 120 secs. Therefore all the green times should be adjusted to suit this condition.

6.2.7 Determination of delays and queues

a) Average delay per vehicle on a particular intersection arm is given by

2 2d = 9 [ C ( I - ~ ) + x ]

--- ------------- ------------10 [ 2 ( l - ~x ) 2q ( l - x ) ]

where d = average delay per vehicle

c = cycle time

~ = proportion of the cycle that is effec-tively green for the phase under consideration ( i.e.g/C )

q = flow

x = degree of saturation, which is the ratio of actual flow to the maximum flow that can pass through the approach ( i.e. q/,.S )

Page 64



To enable the delay to be calculted more easily, the equation is rewritten as.

d = CA + B/q - K

2where A = ( 1 - ~ )

------------- tabulated in fable 6 - 62 ( 1- ~x )

2B = X

------------ tabulated in Table 6 - 72 ( 1 - x )

and K = correction factor tabulated in Table 6 - 8.

Note : User shall use this equation with caution at high degrees of saturation (i.e. x approaches 1) as it will greatly overestimate delay. When x = 1, d =

b) Maximum queue occurs at the start of green and has an average value of

N = q x ror whichever is greater

N = q ( r/2 + d )

where N = number of vehicles q = flow ( veh/sec )

d = average delay per vehicle for a particular arm ( seconds )

r = C - g = effective red time (seconds)

Page 65



To calculate 'Reserve Capacity' use the left hand diagram to obtain a point corresponding to the 'Lost time' and the maximum cycle time suitable for the junction, extend a line horizontally from this point to the right hand diagram to meet a vertical line corresponding with the Y value - the Reserve Capacity ( RC )may be read at the point of intersection. Example : Lost Time 10 seconds; Cycle time 75 seconds; Y value 6; Reserve Capacity 30%.

Page 66



TABLE 6 - 6

Tabulation of A = ( l - ~2 )--------------2 ( l - ~x )

-----------------------------------------------------------------------------------------------------------------------------x 0.1 0.2 0.3 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.80 0.90-----------------------------------------------------------------------------------------------------------------------------O.l 0.409 O.337 0.253 0.319 0.188 O.158 0.132 0.107 0.085 0.066 0.048 0.032 0.0050.2 0.413 0.383 0.261 0.227 0.196 0.166 0.138 0.114 0.091 0.070 0.052 0.024 0.0060.3 0.418 0.340 0.269 0.236 0.205 0.175 0.147 0.121 0.088 0.076 0.067 0.026 0.0070.4 0.422 0.348 0.378 0.246 0.314 0.184 0.156 0.130 0.109 0.003 0.063 0.039 0.0080.5 0.426 0.356 0.288 0.256 0.325 0,195 0.167 0.140 0.114 0.091 0.089 0.033 0.0090.55 0.423 0.360 0.393 0.362 0.231 0.201 0.172 0.145 0.119 0.095 0.073 0.036 0.0100.60 0.431 0.364 0.299 0.267 0.237 0,207 0.179 0.151 0.125 0.100 0.078 0.038 0.0110,65 0.433 0.368 0.304 0.273 0.243 0.214 0.185 0.150 0.131 0.106 0.083 0.042 0.0120.70 0.435 0.372 0.310 0.280 0.250 0.331 0.192 0.165 0.138 0.113 0.088 0.045 0.0140.75 0.438 0.376 0.316 0,286 0.257 0.228 0.200 0.172 0.145 0.120 0.095 0.050 0.0150.80 0.440 0.381 0.322 0.293 0.265 0.236 0.208 0.181 0.154 0.128 0.102 0.056 0.0180.85 0.443 0.386 0.329 0.301 0.373 0.245 0.217 0.190 8.163 0.137 0.111 0.063 0.0210.90 0.445 0,390 0.336 0.300 0.281 0.354 0.227 0.200 0.174 0.148 0.123 0.071 0.0260.92 0.446 0.392 0.388 0.312 8.205 0.258 0.231 0.205 0.179 0.152 0.126 0.076 0.0280.94 0.447 0.394 0.341 0.315 0.280 0.262 0.236 0.210 0.183 0,157 0.133 0.081 0.0320.96 0.448 0.396 0.344 0.318 0.292 0,266 0.240 0.215 0.189 0.163 0.137 0.086 0.0370.98 0.449 0.398 0.347 0.322 0.296 0.271 0.245 0.220 0.194 0.168 0.143 0.083 0.042-----------------------------------------------------------------------------------------------------------------------------

Page 67



TABLE 6 - 7

2Tabulation of B = x

-----------2 ( l - u )

--------------------------------------------------------------------------------------------------x 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09--------------------------------------------------------------------------------------------------0.l 0.006 0.007 0.008 0.0l0 0.0Il 0.013 0.0l5 0.0l7 0.020 0.022

0.2 0.225 0.028 0.031 0.034 0.038 0.042 0.046 0.050 0.054 0.059

0.3 0.064 0.070 0.075 0.081 0.088 0.094 0.101 0.109 0.116 0.125

0.4 0.133 0.I42 0.152 0.162 0.173 0.184 0.l96 0.208 0.222 0.235

0.5 0.350 0.265 0.282 0.299 0.317 0.336 0.356 0.378 0.400 0.425

0.6 0.450 0.477 0.586 0.536 0.569 0.604 0.641 0.680 0.723 0.768

0.7 0.817 0.869 0.926 0.987 1.05 1.13 1.20 1.29 1.38 1.49

0.8 0.60 1.73 1.87 2.03 2.21 2.41 2.64 2.91 3.23 3.60

0.9 4.05 4.60 5.28 6.18 7.36 9.03 11.5 15.7 24.0 49.0--------------------------------------------------------------------------------------------------

Page 68



TABLE 6 - 8

Correction term of equation d = cA + B - Kas a percentage of the first ---two terms q

xM

~ 2.5 5 10 20 40

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.20.40.60.8

0.20.40.60.8

0.20.40.60.8

0.20.40.60.8

0.20.40.60.8

0.20.40.60.8

0.20.40.60.8

2200

6322

10663

141197

18151311

18161514

13121214

2100

4221

4221

11988

14131212

17151515

14131315

1100

3211

5433

8768

11101013

13131417

13131417

1000

2111

3223

5457

77812

10101217

11111417

0000

1101

2122

3335

55610

78915

8121215

Page 69



* M is the average flow per cycle = qc

0.95

0.20.40.60.8

8777

9999

991010

9101112

891013

0.975

0.20.40.60.8

8888

99910

10101112

9101213

891114

Page 70



6.3 GUIDING PRINCIPLES

Some guiding principles to be used in accomplishing the objective of this chapter are as follows :

a) The number of phases should be kept to a minimum : each addi-tional phase reduces the effective green timeavailale for the move-ment. of traffic flows.(Increases lost time due to starting delays and clearance intervalsor intergreen intervals).

b) Short cycle lengths yield the best perform-ance in terms of provid-ing the lowest average delay, provided the capacity of the cycle to pass vehicles is not exceeded.

- For two-phase operations, shortcycle lengths (40to 60 seconds) are generally recommended toproduce mini-mum delay.

- Longer cycle lengths (over 60 seconds) will accommodate more vehicles per hour if there is a constant demand during the entire green

period of each approach. (Longer cycle lengths have a higher capacity since over a given time peri-od, there is a lower frequency of starting delaysand clearance intervals).

- A 120 second cycle length should be the maximum used, irrespective of the number of phases: above a120 second cycle, there is aninsignificant increase in capacity and rapid increase intotal delay.

c) The level of service of the signalised intersec-tion must be the same as the level of service of the road system at that location. See Tables 6.9 and 6.10 below.

Page 71



Table 6 - 9

Level of Service for signalised Intersection

Table 6.10

Level of service of Road

LEVEL OF SERVICE STOPPED DELAY FOR VEHICLE( SEC )

ABCDEF

< 5.05.1 to 15.015.1 to 25.025.1 to 40.040.1 to 60.0

> 60.0

AREAS CATEGORY OF ROAD LEVEL OF SERVICES

RURAL

ExpresswayHighwayPrimary

SecondaryMinor

CCDDE

URBAN ExpresswayArterial

CollectorLocal Street

CDDE


A signal system is defined as havingtwo or more individual signalisedintersections which are link togetherfor coordination purposes. To obtainsystem coordination all signals mustoperate with the same (common)cycle length, although in rareinstances some intersections withinthe system may operate at double orone-half the cycle length of the sys-tem. Although at. individual inter-sections, the intervals (red, green,and yellow) may vary according totraffic conditions, it is desirable thatthe arterial for which coordination isbeing provided have a green plusyellow interval equivalent to at least500 of the cycle length.

7.1 ADVANTAGES

Some of the advantages of providing coordination among signals are :

(i) A higher level of traffic service is provided in terms of higher overall speed and reduced number of stops.

(ii) Traffic should flow more smoothly, often with an improvement incapacity and decrease in energy consumption.

iii) Vehicle speeds should be more uniform because there will be no incentive to travel atexcessively high speedto reach a signalized intersection before the start of the green inter-val, yet slower drivers will be encouraged to speed up to avoid hav-ing to stop for a red light.

(iv) There should be fewer accidents because pla-toons of vehicles will arrive at. each signal when it is green, there-by reducing the possi-bility of red-signal viola-tions or rear-end colli-sions. Naturally, if thereare fewer red intervals displayed to the majori-ty of motorists, there is less likely to be Lroublebecause of driver inat-tention, brake failure, slippery pavement, andso on.

v) Greater obedience to the signal commands should be obtained from both motorists andpedestrian because themotorist will try to keep within the green inter-val,and the pedestrian

Chapter 7

DESIGN OF PROGRESSIVE SIGNAL TIMING

Page 73



will stay at the kerb because the vehicles will be closer, spaced.

(vi) Through traffic will tendto stay on the arterial road instead of on par-allel minor roads.

7.2 APPLICATIONS

In a discussion of the two-wayand one-way street applica-tions of system timing, the fol-lowing terms are frequently used :

1. Through-band : the space between a pair of parallel speed lines which delineates a pro-gressive movement on a time-spare chart.

2. Band speed : the slopeof the through-band representing the pro-gression speed of traf-fic moving along the arterial.

3. Bandwidth : the width of the through-band expressed in seconds (or percent. of cycle length), indicating the period of time availablefor traffic to flow within the band.

7.2.1 One-Way Road

The simplest form of coordi-nating signals is along a one-way road, or to favor one direction of traffic on a two-way road that contains highly directional traffic flows. Essentially, the mathematical relationship between the bandspeed S and the offset L can be described as

S = D-------- (7.1)0.278L

where S = speed of pro-gression (km/hr)

D = spacing of sig-nals (m)

L = offset in seconds

7.2.2 Two-Way Road

For a two-way movement, fourgeneral progressive signal systems are possible : (1) simultaneous, (2) alternate, (3) limited (simple) progres-sive, and (4) flexible progres-sive. The relative efficiency of any of these systems is dependent on the distances between signalized intersec-tions, the speed of traffic, the cycle length, the road-way capacity, and the amount of friction caused by turning vehicles, parking and unpark-ing maneuvers, improper or illegal parking or loading, and

Page 74



pedestrians. In general, a twoway progression with max-imum bandwidths can be achieved only if the signal spacings are such that vehicu-lar travel times between sig-nals are a multiple of one-half the common' cycle length : otherwise, inevitable compro-mises have to be made in the progression design.

In a simultaneous system, all signals along a given street operate with the same cycle length and display the green indication at the same time. Under this system, all traffic moves at one time, and a short time later all traffic stopsat. the nearest signalized intersection to allow cross-road traffic to move.

The mathematical relationshipbetween the band speed (in both directions) and signal spacing in a simultaneous system can be described as follows.

S = D-------- (7.2)0.278C

where S = speed of pro-gression (km/hr)

D = spacing of sig-nals (m)

C = cycle length in seconds

For example, a system of signalized intersections at 1/2 kmspacing could have a band speed in simultaneous system30 km/h, respectively, with a 60 sec cycle. With closely spaced intersections, howev-er, a simultaneous system may encourage excessive speeds as drivers tend to trav-el through a maximum num-ber of intersections during the green interval.

In the alternate system, each successive signal or group of signal shows opposite indica-tions to that of the next. signalor group. If each signal alter-nates with those immediately adjacent, the system is called single alternate. If pairs of sig-nals alternate with adjacent. pairs, the system is termed double alternate: and so on.

The band speed in a single-alternate system is

S = D--------- (7.3) 0.139 C

In a double-alternate system, the band speed is determined by the same formula, with D being the distance between the midpoints of adjacent pairs. Generally speaking, the alternate system may provide excellent traffic; service, depending on the distances between signals and the cyclelength. Equal distances pro-vide the best result.

Page 75



In a simle progressive system, a common cycle length is used and the various signal faces controlling a given road provide green indications in accordance with a time sched-ule to permit continuous oper-ation of platoons along the road at a designed rate of speed, which may vary within different parts of the system.

In a flexible progressive sys-tem, the signal offsets, splits, and/or cycle length of the common cycle are changed tosuit. the needs of traffic : throughout the day. For exam-ple, an inbound progression toward the central business district during the morning peak can be changed to an outbound progression during the remainder of the day merely by adjusting the. signaloffsets, or a longer cycle length can be used during the morning and evening peak hours in order to provide greater capacity than during the off-peak period.

7.3 PROGRESSIVE SIGNALSYSTEM DESIGN

7.3.1 Selection of a cycle length

In the selection of a trial cycle length, the criterion that band speeds be at or near the mean operating speed of vehi-cles on the street is frequentlyused. If the spacing in the system is fairly regular,

equations (7.1) to (7.3) may be solved for C (cycle length) by using the measured oper-ating speed for S and the typi-cal distance between pro-posed signals for D. The resultant cycle lengths falling in a usable range should be compared with the cycle length computed for each indi-vidual intersection. If one cycle length approximates or slightly exceeds those com-puted for a majority of individ-ual intersection it, should be selected on a trial basis. First,however, each individual inter-section must be reexamined to assure that it can operate effectively with the selected cycle length. Sometimes rephasing or geometric and/oroperational improvements at an intersection will be required. If such changes are not feasible, and the operationwith this cycle length would seriously impaired one. or more intersections, a new trialcycle length should be select-ed. In practice, the cycle length already established for signal systems intersection or closely adjacent to the systemunder study will frequently dic-tate the cycle length to be used.

Page 76



7.3.2 Manual design method for arterial routes

To develop an arterial-based timing plan, a considerable amount of data must be col-lected initially, including

(i) Intersection spacing

(ii) Road geometric

(iii) Traffic volumes

(iv) Traffic regulations suchas parking, speed limit, and turn restrictions

(v) Speed and delay infor-mation.

Using the data, a number of timing plans are then deter-mined together with the indi-vidual timing requirements at each signalized location. For each plan a cycle length is -selected which is common to the arterial route, and a graphical analysis of the type illustrated in Figure 7.1. is undertaken by a trial-and-errorprocess to determine offsets for each of the desired timing plans.

Figure 7.1 is a two-dimension-al graph portraying a two-directional coordinated arterialsystem with distance on the horizontal scale and time on the vertical scale. The inter-sections are located on the distance scale with vertical reference lines drawn at the centerline of all signalized

intersections. A horizontal working line'is drawn across the graph on which the green or red phase of each signal-ized intersection at the left edge of the diagram, signal phases are constructed on thevertical reference line with either a green or red phase centered on the working line. A progression speed line which has a slope represent-ing the desired progression speed is drawn starting at the beginning of the green phase at the first signalized intersec-tion. Far each succeeding intersection, either a red or green signal phase is cen-tered on the horizontal work-ing line to obtain an equal bandwidth for each direction of flow. Should progressive movement, be desired in only one direction, this procedure may be modified such that thebeginning of the green phase at each intersection is placed on the progression speed line.

Page 77




BIBLIOGRAPHY

1. "Highway Capacity Manual 1965" - Highway Research Board Special Report 87, Washington DC, 1965.

2. Homburger, Wolfgang S, & Kell, James H, "Fundamentals of TrafficEngineering - 10th Ed., "Institute of Transportation Studies, Univ. ofCalifornia, Berkely, California 1981.

3. Kell, James H & Fullerton, Iris J. "Manual of Traffic Signal Design", Institute of Transportation Engineers, New Jersey 1982.

4. Pignataro, Louis J, "Traffic Engineering, Theory and Practise," Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1973.

5. "Practical Guide for Planning and Design of At-Grade Intersection" - Japan Society of Traffic Engineers, April 1985.

6. "Traffic: Engineering Handbook", Institute of Traffic Engineers, Washington 1965.

7. Webster, F.V. and Cobbe, B.M. "Traffic Signals" - Ministry of Transport,Road Research Technical Paper No. 56, London, April 1966.

8. Yu, Jason C, "Transportation Engineering, Introduction to Planning, Design, and Operations", Elsevier, New York 1982.

Page 79

BIBLIOGRAPHY


Intergreen period : The period of time between the termination of the green signal for one phase and the beginning of the green signal for the next phase to receive right of way.

Interval : A discrete portion of the signal cycle during which the signal indications remain unchanged. Interval Sequence: Specifies theorder in which the various intervals are displayed.

Interval Timing : The passage of time which occurs during an interval.

Loop Detector : A device capable of sensing a change in inductance of aloop sensor imbedded in the roadway caused by the passage or presence of a vehicle over the loop.

Maximum extension : Difference between maximum green and mini-mum green. The normal cycle time + max exten-sion times should preferably not, exceed 120 sees.

Maximum green : The maximum (preset) period a green signal can last after a demand has been made by traffic on another phase.

Magnetometer : A device capable of being actuated by the magnetic dis-turbance caused by the passage or presence of a vehi-cle. A magnetic flux generator/sensor is installed in the roadway and connected to sensor applifier electronics.

Measures ofEffectiveness(MOEs) : Indices of the effectiveness of the system in

improving traffic flow. Common bases of compari-son include congestion, density, lane occupancy, stops, delay, and queue length.

Minimum green : The shortest period of time a green signal may be dis-played during any phase.

Occupancy : The percentage of roadway occupied by vehicles at aninstant in time. In general use, it is a measurement based upon the ratio of vehicle presence time (as indi-cated by a presence detector) over a fixed per:rod of total time.

Page 80

BIBLIOGRAPHY


Offset : The time difference or interval in seconds between the start of the green indication at one intersection as related to the start ofthe green interval at another intersection or from a system time base.

Offset Selection : Choosing one of several possible offsets either manuallyor automatically either by time-of-day or in response to some directional characteristics of traffic flow.

Parameter : (1) A quantity in mathematics that, may be assigned any arbitrary value and that remains constant during some calculation; (2) a definable characteristics of an item, device, or system.

Pattern : A unique set. of traffic parameters (cycle, split., and offset) associated with each signalized intersection within a predefinedgroup of intersection (a section or subzone)

Phase : A part of the traffic signal time cycle: allocated to any combina-tion of traffic movements receiving right of way simultaneously during one or more intervals.

Phase Overlap : Refers to a phase which operates concurrently with one or more other phases.

. Phase Sequence : The order in which a controller cycles through all phases.

Plan : A plan gives the relationship between phases and signal groupsin terms of time. The possibilities of a plan can be laid down in a time cycle diagram of one or more intersection control units.

Presence Detection : The sensing of a vehicle passing over a detector. True presence is when the pulse duration is equalto the actual time the vehicle remains in the detector field of influence.

Primary Signal Face : The signal face which is nearest to and facing on-coming traffic. It is ordinarily situated on the near side of the carriageway facing approaching traffic,but may be duplicated on the off-side.

Recall : An operational mode for an actuated intersection controller whereby a phase, either vehicle or pedestrian is displayed eachcycle whether demand exists or not. Usually a temporary emer-gency situation.

Page 81

BIBLIOGRAPHY


Relay : An electromagnetic switching device, having multiple electrical contacts, energized by electrical current through its coil. It is used to completed electrical circuits.

Saturation flow : The maximum flow that can pass through an intersectionapproach under prevailing traffic and roadway condi-tions, assuming that the approach had 100% of real timeavailable as effective green time.

Secondary Signal Face : A signal face facing on-coming traffic supplement-ing the primary signal face and remote from it.

Signal group : A set of one or more signal indications which are switched on and off simultaneously.

Signal Head : An assembly containing one or more signal faces that may be designated accordingly as one-way, two-way, etc.

Signal Indication : The following of a traffic signal lens or equivalent device or a combination of several lenses or equivalent: devicesat the same time.

Signal face : That. part, of a signal head that contains lenses and associatedcomponents (such as bulbs, reflectors, visors) provided for controlling traffic in a single direction. Turning indications may be included in a signal face.

Split : A percentage of the cycle length allocated to each of the various phases in a signal sequence.

Stops : The number of times vehicles stop in the system. Used as a measure of effectiveness to assess the effectiveness of a tim-ing pattern. A computer controlled system goal is to minimize stops.

traffic : Vehicles, persons or animals, traveling on a highway considered collectively.


APPENDIX A

Design Example This example consists of step by step design calculations to further explain the concepts found in Chapter 6. The junction's geometric and traffic flow values for

this design example are only hypothetical

Page 83

APPENDIX A


Page 84

APPENDIX A


2. Peak-hour flows

The peak-hour flows are obtained from 16-hour classified traffic counts and data are converted into pcu's by using the factors in Table 6-5. The converted values are as shown :-

Page 85

APPENDIX A


An average value of the morning and evening peak is than tabulated.

Projected design values

Lets say the project will be implemented the following year.

So, n = 1 and with GR = 5% (assume).

1PCU = PCU x (1.05)

future present

With this formula the following design values are use for signal design calculations.

FROM APPROACH DIRECTION

NORTH Total pcu : 218 LT : 48ST : 135RT : 35

SOUTH Total pcu : 281LT : 53

ST : 180RT : 48

EAST Total pcu : 439LT : 78

ST : 193RT : 168

WEST Total pcu : 423LT : 98

ST : 145RT : 180

Page 86

APPENDIX A


Design value

Approach from Total pcu Movement pcu

NORTH 229LT : 50

ST : 142RT : 37

SOUTH 295LT : 56

ST : 189RT : 50

EAST 461LT : 82

ST : 203RT : 176

WEST 444LT : 103ST : 152RT : 189

Page 87

APPENDIX A


3. Saturation flows

The information for the approaches permits the following calculations :

NORTH : S = 1965 pcu/hr for W = 4.Om ( from table 6-1 )

Factors

Gradient : Fg = 1.09 for -3% grade ( table 6-2 )Left-turnTraffic : ( 50/229)x100%=22%, F1=0.98 ( table 6-4 ) Right-turnTraffic : (37/229)x100%=16%, Fr= 0.90 ( table-6-4 )

Adjusted saturation flow

S = S x Fg x F1 x Fr= 1965 x 1.09 x 0.98 x 0.90 = 1889 pcu/hr

SOUTH : S = 1965 pcu/hr for W = 4.Om (from table 6-1)

Factors

Gradient : Fg = 0.91 for +3% grade ( table 6-2 ) Left-turnTraffic : ( 56/295)x100%=19%, F1=0.98 ( table 6-4 ) Right-turnTraffic : ( 50/295)x100%=17%, Fr=0.89 ( table 6-4 )


Ss = S x Fg x Fl x Fr= 1965 x 0.91 x 0.98 x 0.89 = 1560 pcu/hr

Page 88

APPENDIX A


EAST :a) Left Lane :

S = 1915 pcu/hr for W = 3.75 m ( from table 6-1 )

Factors

Gradient : Fg = 1.0 for level grade ( table 6-2 ) Left-turnTraffic : (82/285)x100%=29%, F1=0.95 ( table 6-4 )


S = S x Fg x FlEL

= 1915 x 1.0 x 0.95 = 1819 pcu/hr

b) Right Lane :


Factors

Gradient : Fg = 1.0 for level grade ( table 6-2 ) TurningRadius : Ft = 0.85 for R < 10m ( table 6-3 )


S = S x Fg x Ft ER= 1915 x 1.0 x 0.85 = 1628 pcu/hr

Page 89

APPENDIX A


WEST :a) Left Lane :


Factors

Gradient : Fg = 1.0 for level grade ( table 6-2 ) Left-turnTraffic : ( 103/255)x100%=40%, F1=0.93 ( table 6-4 )


S = S x Fg x F1EL

= 1915 x 1.0 x 0.93 = 1781 pcu/hr

b) Right Lane :


Factors

Gradient : Fg = 1.0 for level grade ( table 6-2 ) TurningRadius : Ft = 0.85 for R < 10 m ( table 6-3 )


S = S x Fg x FtER

= 1315 x 1.0 x 0.85 = 1628 pcu/hr

Page 90

APPENDIX A


The next step is to determine the phasing for the intersection.

For the purpose of this example, let's consider a 3 phase fixed time trafficsignal with the phases including pedestrian phase are as shown below.

Page 91

APPENDIX A


Y - VALUE

EY = 0.157 + 0.116 + 0.189= 0.462

SINCE EY < 0.85 ( Which is the limiting value )WE CAN PROCEED WITH THE TIMING CALCULATIONS.

PHASE ¢1 ¢2 ¢1

MOVE MENTIDENTIFICATION

WL EL WR ER M S

q 225 285 189 179 229 295

s 1781 1817 1628 1628 1889 1560

q/s 0.143 0.157 0.116 0.108 0.121 0.189

Y 0.157 0.116 0.189

Page 92

APPENDIX A


5. Amber time, a

The amber time (a) for the North and South approaches are the same since vehicles from that approach has to travel 12.25m to clear the intersection.

a = 13.4 m/s 12.25 m + 5.5 mN and S ----------------- + ----------------------

2 x 4.58 m/s 13.4 m/s

= 2.79= 3 seconds

a = 13.4 m/s 9 m + 5.5 mE and W ----------------- + -------------------

2 x 4.58 m/s 13.4 m/s

= 2.54= 3 seconds

Use a = 3 seconds

6. Intergreen time, I

I = a + R

where R = all red interval ( taken as 2 seconds )

Therefore, I = 3 + 2= 5 seconds

7. Total lost time, L

n nL = E ( I - a ) + E 1

i=1 i=1

= 3 ( 5-3 ) + 3 ( 2 )= 12 seconds

Page 93

APPENDIX A


8. Optimum cycle time, Co

Co = 1.5L + 5-----------

1 - Y

= 1.5 ( 12 ) + 5------------------

1 - 0.462

= 43 seconds

Design Co can be between 0.75 to 1.50 of the calculated Co.

For simplicity, take design Co = 60 seconds

9. Total effective green time

Total effective green time = Co - L= 60 - 12 = 48 seconds

10. Effective green time, g

g = y ( C - L )--Y

g = 0.157 ( 48 ) 01 ---------------

0.462= 16 seconds

g = 0.116 ( 48 ) 02 ---------------

0.462= 12 seconds

g = 0.189 ( 48 ) 03 ---------------

0.462= 20 seconds

Page 94

APPENDIX A


11. Actual Green Time, G

Gi = g i + l i + R i

( in this worked example, all the 1's and R's are the same for every phase ).

G 01 = 16 + 2 + 2 = 20 seconds

G 02 = 12 + 2 + 2 = 16 seconds

G 03 = 20 + 2 + 2 = 24 seconds

12. Check for pedestrian requirement for green time

G = 5 + Wped ------ - I

1.22

( Note: Check only the critical pedestrian crossings where W is the widest )

G = 5 + 9 - 5------1.22

= 7.38= 8 seconds

In our calculations, green time available for pedestrian crossing is in phase 1.

G = 20 seconds, therefore it is O.K.

Page 95

APPENDIX A


13. Controller setting time, K

K i = G i - a - R

K 01 = 20 - 3 - 2 = 15 seconds

K 02 = 16 - 3 - 2 = 11 seconds

K 03 = 24 - 3 - 2 = 19 seconds

15. Reserve Capacity of Junction

R.C. = 0.9 ( 1-L ) - Y---Cm

------------------- x 100%Y

Let Cm = 120 seconds

From the above calculations : L = 12 seconds, Y = 0.462

R.C. = 0.9 ( 1-12/120 ) - 0.462 -------------------------------- x 100%

0.462= 75%

The Reserve Capacity Diagram, by using Figure A - 2, RC = 75%.

Page 96

APPENDIX A


16. Design Life of the junction, n

n = log ( Q1/Qo )-----------------log ( 1 + GR )

Assume GR = 5%

Q is the practical capacity that can be accomodated with 120 seconds cycle. For ease, the variables for each approach are tabulated as below.

Page 97

APPENDIX A


Note : The above g values are calculated when Co = 120 sec

Then check for various movements.

N : Ql = 624Go = 229 n = log ( 624/229 )GR = 5% --------------------

log ( 1 + 0.05 )

= 21 years

S : Ql = 515 n = log ( 515/295 )Qo = 295 -------------------GR = 5% log ( 1 + 0.05 )

= 11 years

WL : 01 = 494 n = log ( 494/255 ) Qo = 255 -------------------GR = 5% log ( 1 + 0.05 )

= 14 years

Movement N S WL

WR

EL

ER

Sg

CoCapacity

Q = gS / C90% ult.cap Ql

Present flow Qo

188944120

693

624

229

156044120

572

515

295

178137120

549

494

255

162827120

366

329

189

181937120

561

505

285

162827120

366

329

176

Page 98

APPENDIX A


WR : Q1 = 329 n = log ( 329/189 )Go = 189 -------------------GR = 5% log ( 1 + 0.05 )

= 11 years

EL : Q1 = 505Go = 285 n = log ( 505/285 )GR = 5% -------------------

log ( 1 + 0.05 )

= 12 years

ER : Q1 = 329Qo = 176 n = log ( 329/176 )GR = 5% -------------------

log ( 1 + 0.05 )

= 13 years

Design Life, n = 11 years

17. Delays

N : q = 229 pcu/hr = 229/3600 pcu/sec S = 1889 pcu/hrg = 20 C = 60

~ = g/C = 20/60 = 0.333

x = q = 229-----------------

~S 0.33 ( 1889 )

= 0.36

Page 99

APPENDIX A


dN = 9 [ 60 ( 1-0.333 )² 0.362² ]--- ------------------------- + --------------------------10 [ 2( 1-0.333x0.36 ) 2 ( 229 )( 1-0.36 ) ]

--------3600

= 0.9 ( 15.16 + 1.59 )

= 15 seconds

S : q = 295 pcu/hr = 295/3600 pcu/sec S = 1560 pcu/hrg = 20C = 60

~ = 9/C = 20/60 = 0.333

x = q = 295--- -----------------~S 0.33 ( 1560 )

= 0.57

dS = 9 [ 60 ( 1-0.333 )² 0.572² ]--- ------------------------ + ---------------------------10 [ 2( 1-0.333x0.57 ) 2( 295 ) ( 1-0.577 ) ]

--------3600

= 0.9 ( 16.47 + 4.61 )

= 19 seconds

WL : q = 255 pcu/hr = 255/3600 pcu/sec S = 1781 pcu/hrg = 16 C = 60

~ = g/C = 16/60 = 0.27

x = q = 255--- -----------------~S 0.27 ( 1781 )

= 0.53

Page 100

APPENDIX A


dWL = 9 [ 60 ( 1-0.27 )² 0.532² ]

--- ---------------------- + ---------------------------10 [ 2 ( 1-0.27x0.53 ) 2( 255 ) ( 1-0.53 ) ]

--------3600

= 0.9 ( 18.66 + 4.22 )

= 21 seconds

WR = q = 189 pcu/hr = 189/3600 pcu/sec S = 1628 pcu/hrg = 12 C = 60

~ = g/C = 12/60 = 0.2

x = q = 189--- ---------------~S 0.2 ( 1628 )

= 0.58

d = 9 [ 60 (1-0.2 )² 0.582² ]WR --- --------------------- + ----------------------------

10 [ 2( 1-0.2x0.58 ) 2( 189 ) ( 1-0.58 ) ]-------3600

= 0.9 ( 21.72 + 7.63 )

= 26 seconds

EL : q = 285 pcu/hr = 285/3600 pcu/sec S = 1819 pcu/hrg = 16 C = 60

~ = g/C = 16/60 = 0.27

Page 101

APPENDIX A


x = q = 285--- -------------------~S 0.27 ( 1819 )

= 0.58

dEL = 9 [ 60(1-0.27)² 0.58² ]--- ---------------------- + ------------------------10 [ 2( 1-0.27x0.58 ) 2( 285) (1-0.58) ]

-------3600

= 0.9 ( 18.96 + 5.06 )

= 22 seconds

ER : q = 176 pcu/hr = 176/3600 pcu/sec S = 1628 pcu/hrg = 12 C = 60

~ = g/C = 12/60 = 0.2

x = q = 176 --- ----------------~S 0.2 ( 1628 )

= 0.54

dER = 9 [ 60 ( 1-0.2 )² 0.542² ]--- ---------------------- + --------------------------10 [ 2 ( 1-0.2x0.54 ) 2( 176 ) ( 1-0.54 ) ]

-------3600

= 0.9 ( 21.52 + 6.48 )

= 25 seconds

Therefore movement WR will experience the worst delay of 26 seconds per vehicle. Its condition will be in the level of service D. Other approaches will be in level of service C.

Page 102

APPENDIX A


18. Queue lengths, N

NORTH : q = 229 pcu/hr g = 20 sC = 60 s d = 15 s r = 40 s

a) N = 229 x 40 = 2.54 pcu ------------

3600

Assume 1 vehicle = 1.2 pcu. This value depends on the composition of the present traffic flow i.e. if more medi-um and heavy vehicles than cars, the value should be more than 1.

N = 2.54/1.2= 2.12 vehicles

b) N = 229 ( 40/2 + 15 ) -----------------------

3600

= 2.23 pcu= 2.23/1.2 vehicles = 1.86 vehicles

Therefore, the North approach will experience an aver-age queue length of 2.1 vehicles.

SOUTH : q = 295 pcu/hr g = 20 sC = 60 s d = 19 s r = 40 s

a) N = 295 x 40 = 3.28 pcu ------------3600

= 3.28/1.2= 2.73 vehicles

Page 103

APPENDIX A


b) N = 295 ( 40/2 + 19 )----------------------

3600


Therefore, the South approach will experience an aver-age queue length of 2.73 vehicles.

WEST : q = 255 pcu/hrg = 16 s C = 60 s d = 21 s r = 44 s

a) N = 255 x 44 = 3.12 pcu ------------

3600

= 3.12/1.2= 2.6 vehicles

b) N = 255 ( 44/2 + 21 )-----------------------

3600


Therefore, the West left lane approach will experience an average queue length of 2.6 vehicles.

Page 104

APPENDIX A


WESTR : q = 189 pcu/hr g = 12 sC = 60 s d = 26 s r = 48 s

a) N = 189 x 48 = 2.52 pcu ------------

3600

N = 2.52/1.2= 2.1 vehicles

b) N = 189 ( 48/2 + 26 )----------------------

3600


Therefore, the West right lane approach will experience an average queue length of 2.19 vehicles.

EASTL : q = 285 pcu/hr g = 16 sC = 60 s d = 22 s r = 44 s

a) N = 85 x 44 = 3.48 pcu ----------

3600

= 3.48/1.2= 2.9 vehicles

b) N = 285 ( 44/2 + 22 ) ----------------------

3600


Page 105

APPENDIX A


Therefore, the East left lane approach will experience anaverage queue length of 2.9 vehicles.

EASTR : q = 176 pcu/hr g = 12 sC = 60 s d = 25 s r = 48 s

a) N = 176 x 48 = 2.35 pcu ------------

3600

= 2.35/1.2= 1.96 vehicles

b) N = 176 ( 48/2 + 25 )----------------------

3600

= 2.4 pcu= 2.4/1.2 vehicles = 2 vehicles

Therefore, the East right lane approach will experience an average queue length of 2 vehicles.


APPENDIX B

Vehicle - actuated Signal Facilities

Page 107

APPENDIX B


Vehicle-actuated signals havelargely replaced fixed-time signalsbecause of their greater flexibilityunder varying traffic conditions. Withvehicle-actuated signals severalfacilities are available to increase theresponse of the signals to trafficdemand; one of these is the mini-mum green period.

The minimum green period isthe shortest. period of right of waythat. is given to any phase. It is longenough to clear the vehicles waitingbetween the detector loop and thestop line. Modern controllers haveminimum green periods that varybetween 7 and 13s, according to thenumber of vehicles that have passedthe detector and are waiting at, thestop line.

The minimum green periodmay be extended beyond the mini-mum value as vehicles pass over thedetector on the approach. With amodern signal controller the length ofthis vehicle extension period is relat-ed to the measured speed ofapproach at the detector. Thesevehicle extension periods are individ-ually and not. cumulatively set sothat the green period is not reset if anew vehicle extension period calcu-lated by the controller does notexceed the unexpired portion of theprevious controller.

If an interval of time betweenvehicles crossing the detectorbecomes greater than the last. vehi-cle extension period, and if there hasbeen a demand for the green signalon another phase, then a 'gapchange' takes place and the right ofway is transferred.

The application of successive-vehicle extension periods wouldresult in a continuous green indica-tion if there was a continuous pas-sage of vehicles along the approach.To limit the length of the green peri-od there is preset maximum greenperiod, which is normally set at, avalue between 8 and 68s, althoughon holiday routes some controllersallow this period to be increased bya further two minutes.

When signals run to maximumgreen then, on the expi.ry of themaximum green period on the otherphase or phases, provision is madefor the return of the right. of way tothe original phase.

In practice when traffic isheavy on all approaches, the signalsrun to maximum green on all phasesand in effect give fixed-time opera-tion.

A variation of this maximumgreen period is the variable maxi-mum period. This facility allows themaximum green to be extended ifthe flow at the end of the maximumgreen period exceeds a certain criti-cal value. This critical value is con-stantly increased until it exceeds themeasured flow or a gap changeoccurs.

Note : This article is taken from 'Highway Traffic Analysis and Design' Rev. Ed. London: The Mac Millan Press Ltd, 1976 by R.J. Salter.

Arahan Teknik (Jalan) 13-87 - A Guide to the Design of Traffic Signal

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