It deals with visible elements of a highway. It is influenced by: Nature of terrain. Type Composition and hourly volume / capacity of traffic Traffic.

It deals with visible elements of a highway.

It is influenced by:• Nature of terrain.• Type• Composition and hourly volume / capacity of traffic• Traffic Factors• Operating speed (Design Speed)• Landuse characteristics (Topography)• Environmental Factors (Aesthetics).

TERRAIN CLASSIFICATION

Terrain type Percentage cross slope

of the country

Plain 0-10

Rolling 10-25

Mountainous 25-60

Steep >60

• Maximize the comfort

• Safety,

• Economy of facilities

• Sustainable Transportation Planning.

• geometric cross section

• vertical alignment

• horizontal alignment

• super elevation

• intersections

• various design details.

HIGHWAY GEOMETRIC DESIGN

• Cross sectional elements

• Sight distance

• Horizontal curves

• Vertical curves

Comparision of Urban and Rural Roads

Section Capacity

Peak Hour flow

Traffic fluctuations

Design Based on ADT

Speed

Urban Road Classification

• ARTERIAL ROADS• SUB ARTERIAL• COLLECTOR• LOCAL STREET• CUL-DE-SAC• PATHWAY • DRIVEWAY

Urban Road Classification

• ARTERIAL ROADS

• SUB ARTERIAL• COLECTOR• LOCAL STREET• CUL-DE-SAC• PATHWAY • DRIVEWAY

ARTERIAL

• No frontage access, no standing vehicle, very little cross traffic.

• Design Speed : 80km/hr• Land width : 50 – 60m• Spacing 1.5km in CBD & 8km or more in

sparsely developed areas.• Divided roads with full or partial parking• Pedestrian allowed to walk only at

intersection

SUB ARTERIAL

• Bus stops but no standing vehicle.

• Less mobility than arterial.

• Spacing for CBD : 0.5km

• Sub-urban fringes : 3.5km

• Design speed : 60 km/hr

• Land width : 30 – 40 m

Collector Street• Collects and distributes traffic from local

streets• Provides access to arterial roads• Located in residential, business and

industrial areas.• Full access allowed.• Parking permitted.• Design speed : 50km/hr• Land Width : 20-30m

Local Street• Design Speed : 30km/hr.• Land Width : 10 – 20m.• Primary access to residence, business or

other abutting property• Less volume of traffic at slow speed• Origin and termination of trips.• Unrestricted parking, pedestrian movements.

(with frontage access, parked vehicle, bus stops and no waiting restrictions)

CUL–DE- SAC

• Dead End Street with only one entry access for entry and exit.

• Recommended in Residential areas

HIGHWAY CROSS SECTIONAL ELEMENTS

1.Carriage way (Pavement width)

2.Camber

3.Kerb

4.Traffic Separators

5.Width of road way or formation width

6.Right of way (Land Width)

7.Road margins

8.Pavement Surface

(Ref: IRC 86 – 1983)

• The primary consideration in the design of cross sections is drainage.

• Highway cross sections consist of traveled way, shoulders (or parking lanes), and drainage channels.

• Shoulders are intended primarily as a safety feature.

• Shoulders provide:

– accommodation of stopped vehicles

– emergency use,

– and lateral support of the pavement.

– Shoulders may be either paved or unpaved.

– Drainage channels may consist of ditches (usually grassed swales) or of paved shoulders with berms of curbs and gutters.

Two-lane highway cross section, with ditches.

Two-lane highway cross section, curbed.

Two-lane highway cross section, curbed.

Divided highway cross section, depressed median, with ditches.

• Standard lane widths are 3.6 m (12 ft).

• Shoulders or parking lanes for heavily traveled roads are 2.4 to 3.6 m (8 to 12 ft) in width.

• narrower shoulders used on lightly traveled road.

CARRIAGE WAY (IRC RECOMMENDATIONS)

Single lane without Kerbs = 3.50m Two lane without kerbs = 7m Two lane with kerbs = 7.5m 3 lane with or without kerbs = 10.5 /11.0 4 lane with or without kerbs = 14.0m 6 lane with or without kerbs = 21.0 m Intermediate carriage way = 5.5m Multilane pavement = 3.5m/lane

Footpath (Side walk)

No of Persons/Hr Required Width of footpath (m)

All in one direction

In both direction

1200 800 1.5

2400 1600 2.0

3600 2400 2.5

4800 3200 3.0

6000 4000 4.0

Cycle Track

• Minimum = 2m• Each addln lane = 1m• Separate Cycle Track for peak hour

cycle traffic more than 400 with motor vehicle of traffic 100 – 200 vehicles/Hr.

• Motor Vehicles > 200; separate cycle track for cycle traafic of 100 is sufficient.

MedianWidth of Median Depends on:

– Available ROW– Terrain– Turn Lanes– Drainage.

Mim Width of Median:– Pedestrian Refuge =1.2m– To protect vehicle making Right turn = 4.0m (Recc – 7.0m)– To protect vehicle crossing at grade = 9 – 12m.– For Urban area 1.2 to 5m

KERBS

• Road kerbs serve a number of purposes: • - retaining the carriageway edge to prevent

'spreading' and loss of structural integrity • - acting as a barrier or demarcation between

road traffic and pedestrians or verges • - providing physical 'check' to prevent vehicles

leaving the carriageway • - forming a channel along which surface water

can be drained

KERBS• Low or mountable kerbs : height = 10 cm provided at medians and

channelization schemes and also helps in longitudinal drainage.

• Semi-barrier type kerbs : When the pedestrian traffic is high. Height is 15 cm above the pavement edge. Prevents encroachment of parking vehicles, but at acute emergency it is

possible to drive over this kerb with some difficulty.

• Barrier type kerbs : Designed to discourage vehicles from leaving the pavement. They are provided when there is considerable amount of pedestrian traffic.

Height of 20 cm above the pavement edge with a steep batter.

• Submerged kerbs : They are used in rural roads. The kerbs are provided at pavement edges between the pavement edge

and shoulders. They provide lateral confinement and stability to the pavement.

CAMBER (OR) CROSS FALL

S. NoType of Surface

% of camber in rainfall range Heavy to light

1 Gravelled or WBM surface 2.5 % - 3 %

( 1 in 40 to 1 in 33)

2 Thin bituminous Surface 2.0 % - 2.5 %( 1 in 50 to 1 in 40)

3 Bituminous Surfacing or Cement Concrete surfacing

1.7 % - 2.0 %

4 Earth 4 % - 3 %

Types of Camber

• Parabolic or Elliptic

• Straight Line

• Straight and Parabolic

29

Sight Distances

The actual distance along the road surface up to which the driver of a vehicle sitting at a specified height has visibility of any obstacle.

The visibility ahead of the driver at any instance.

SIGHT DISTANCE

THE SIGHT DISTANCE AVAILABLE ON A ROAD TO A DRIVER DEPENDS ON

– FEATURE OF ROAD AHEAD

– HEIGHT OF THE DRIVER’S EYE ABOVE THE ROAD SURFACE

31

Sight Distances

1. Stopping Sight distance

2. Over Taking Sight distance

3. Passing

4. Intermediate

32

Sight Distance in Design• Stopping Sight Distance (SSD) – object in

roadway

• Passing Sight Distance (PSD) – pass slow vehicle

Stopping Sight Distance (SSD)

THE DISTANCE WITHIN WHICH A MOTOR VEHICLE CAN BE STOPPED DEPENDS ON

– Total reaction time of driver– Speed of vehicles– Efficiency of brakes– Gradient of road– Frictional resistance

TOTAL REACTION TIME

• PERCEPTION TIME

• BRAKE REACTION TIME

TOTAL REACTION TIME DEPENDS ONPIEV THEORY

• PERCEPTION

• INTELLECTION

• EMOTION

• VOLIATION

36

Perception-Reaction Process

• Perception

• Identification

• Emotion

• Reaction (volition)

PIEVUsed for Signal Design and Braking Distance

37

Perception-Reaction Process• Perception

– Sees or hears situation (sees deer)• Identification

– Identify situation (realizes deer is in road)• Emotion

– Decides on course of action (swerve, stop, change lanes, etc)

• Reaction (volition)– Acts (time to start events in motion but not

actually do action) • Foot begins to hit brake, not actual

deceleration

38

Typical Perception-Reactiontime range

0.5 to 7 seconds

Affected by a number of factors.

39

Perception-Reaction Time Factors

• Environment• Urban vs. Rural• Night vs. Day• Wet vs. Dry

• Age

• Physical Condition• Fatigue• Drugs/Alcohol

• Distractions

40

Age• Older drivers

– May perceive something as a hazard but not act quickly enough

– More difficulty seeing, hearing, reacting

– Drive slower– Less flexible

41

Age• Younger drivers

– Quick Response but not have experience to recognize things as a hazard or be able to decide what to do

– Drive faster– Are unfamiliar with driving experience– Are less apt to drive safely after a few drinks– Are easily distracted by conversation and others inside

the vehicle– May be more likely to operate faulty equipment.– Poorly developed risk perception– Feel invincible, the "Superman Syndrome”

42

Alcohol

• Affects each person differently

• Slows reaction time

• Increases risk taking

• Dulls judgment

• Slows decision-making

• Presents peripheral vision difficulties

43

Stopping Sight Distance (SSD)• Required for every point along alignment

(horizontal and vertical) – Design for it, or sign for lower, safe speed.

• Available SSD = f(roadway alignment, objects off the alignment, object on road)

• SSD = LD + BD

Lag distance

Braking Distance

Lag Distance

• Speed of the vehicle = v m/sec• Reaction Time of Driver = t sec ; (2.5 sec)

• Lag Distance = v t m• If the design speed is V kmph,• Lag Distance = V x 1000 x t

60 x 60

= 0.278 V t m

Braking DistanceKinetic Energy at the design speed of v m/sec= ½ m v2

= W v2 ; m = W/g 2g

W = weight of the VehicleG = acceleration due to gravity (9.9 m/sec2)Work done in stopping the vehicle = F x lF = Frictional forceL = braking distanceF = coeff of friction = 0.35

Wv2 = fWl ; l = v2

2g 2fg

46

SSD Equation

SSD,m = 0.278V t + _____V2_____ 254f

SSD in meter

V = speed in kmph

T = perception/reaction time (in seconds)

f = design coefficient of friction

STOPPING SIGHT DISTANCE FOR ASCENDING GRADIENT AND

DESCENDING GRADIENT

SSD = 0.278vt + v2

2g(f+ (n/100))

(or)

SSD = 0.278Vt + V2

254(f - n/100)

Passing Distance

• Applied to rural two-lane roads• The distance required for a vehicle to safely overtake

another vehicle on a two lane, two-way roadway and return to the original lane without interference with opposing vehicles

• Designers assume single vehicle passing• Several assumptions are considered (vehicle being

passed s traveling at a uniform speed, and others)• Normally use car passing car• Passing distance increased by type of vehicle• Minimum passing distance currently used are

conservative

Geometric Design of Highways

• Highway Alignment is a three-dimensional problem– Design & Construction would be difficult in 3-D so

highway alignment is split into two 2-D problems

Horizontal Alignment

• Components of the horizontal alignment.

• Properties of a simple circular curve.

Horizontal Alignment

Tangents Curves

Tangents & Curves

Tangent

Curve

Tangent to Circular Curve

Tangent to Spiral Curve toCircular Curve

TWO CURVES

• HORIZONTAL CURVES

• VERTICAL CURVES

Stationing

Horizontal Alignment

Vertical Alignment

Alignment Design

Definition of alignment: Definitions from a dictionary In a highway design manual: a series of straight lines

called tangents connected by circular curves or transition or spiral curves in modern practice

1. Definition of alignment design: also geometric design, the configuration of horizontal, vertical and cross-sectional elements (first treated separately and finally coordinated to form a continuous whole facility)

Horizontal alignment design1. Components of horizontal alignment

Tangents (segments of straight lines)Circular/simple curvesSpiral or transition curves

Alignment Design2. Horizontal curves

Simple curves

This consists of a single arc of uniform radius connecting two tangents

Compound curves A compound curve is formed by joining

a series of two or more simple curves of different radius which turn in same direction..

Simple curve elements

Simple curve in full superelevation

Compound curve

Alignment Design2. Horizontal curves

TRANSITION CURVEA curve having its radius varying gradually from a

radius equal to infinity to a finite value equal to that of a circular curve

Reverse curvesA circular curve consistings of two simple curves

of same or different radii and turn in the opposite direction is called reverse curve

61 Monday, April 10, 2023

Reverse curves

The vertical alignment of a transportation facility consists of

• tangent grades (straight line in the vertical plane)

• vertical curves. Vertical alignment is documented by the profile.

Vertical Alignment

Vertical curves

Convex and concave curves

Vertical Alignment

• Objective: – Determine elevation to ensure

• Proper drainage• Acceptable level of safety

• Primary challenge– Transition between two grades– Vertical curves

G1 G2G1

G2

Crest Vertical Curve

Sag Vertical Curve

Coordination of vertical and horizontal alignments

Outline

1. Concepts2. Vertical Alignment

a. Fundamentalsb. Crest Vertical Curvesc. Sag Vertical Curvesd. Examples

3. Horizontal Alignmenta. Fundamentalsb. Superelevation

4. Other Non-Testable Stuff

Concepts

• Alignment is a 3D problem broken down into two 2D problems– Horizontal Alignment (plan view)– Vertical Alignment (profile view)

• Stationing– Along horizontal alignment– 12+00 = 1,200 ft.

Piilani Highway on Maui

Stationing

Horizontal Alignment

Vertical Alignment

From Perteet Engineering

Vertical Alignment

Vertical Alignment

• Objective: – Determine elevation to ensure

• Proper drainage• Acceptable level of safety

• Primary challenge– Transition between two grades– Vertical curves

G1 G2G1

G2

Crest Vertical Curve

Sag Vertical Curve

Vertical Curve Fundamentals

• Parabolic function– Constant rate of change of slope– Implies equal curve tangents

• y is the roadway elevation x stations (or feet) from the beginning of the curve

cbxaxy 2

Vertical Curve Fundamentals

G1

G2

PVI

PVT

PVC

L

L/2

δ

cbxaxy 2

x

Choose Either:• G1, G2 in decimal form, L in feet• G1, G2 in percent, L in stations

RelationshipsChoose Either:• G1, G2 in decimal form, L in feet• G1, G2 in percent, L in stations

G1

G2

PVI

PVT

PVC

L

L/2

δ

x

1 and 0 :PVC At the Gbdx

dYx

cYx and 0 :PVC At the

L

GGa

L

GGa

dx

Yd

22 :Anywhere 1212

2

2

Example

A 400 ft. equal tangent crest vertical curve has a PVC station of 100+00 at 59 ft. elevation. The initial grade is 2.0 percent and the final grade is -4.5 percent. Determine the elevation and stationing of PVI, PVT, and the high point of the curve.

G1=2.0%

G2= - 4.5%

PVI

PVT

PVC: STA 100+00EL 59 ft.

G1=2.0%

G2= -4.5%

PVI

PVT

PVC: STA 100+00EL 59 ft.

Other Properties

G1

G2

PVI

PVTPVC

x

Ym

Yf

Y

2

200x

L

AY

800

ALYm

200

ALY f

21 GGA

•G1, G2 in percent•L in feet

Other Properties

• K-Value (defines vertical curvature)– The number of horizontal feet needed for a

1% change in slope

A

LK

1./ GKxptlowhigh

Crest Vertical Curves

G1G2

PVI

PVTPVC

h2h1

L

SSD

221

2

22100 hh

SSDAL

A

hhSSDL

2

212002

For SSD < L For SSD > L

Line of Sight

Crest Vertical Curves

• Assumptions for design– h1 = driver’s eye height = 3.5 ft.

– h2 = tail light height = 2.0 ft.

• Simplified Equations

2158

2SSDAL

ASSDL

21582

For SSD < L For SSD > L

Crest Vertical Curves

• Assuming L > SSD…

2158

2SSDK

Design Controls for Crest Vertical Curves

from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001

Design Controls for Crest Vertical Curves

fro

m A

AS

HT

O’s

A P

olic

y o

n G

eo

me

tric

De

sig

n o

f H

igh

wa

ys a

nd

Str

ee

ts 2

00

1

Sag Vertical Curves

G1 G2

PVI

PVTPVC

h2=0h1

L

Light Beam Distance (SSD)

tan200 1

2

Sh

SSDAL

A

SSDhSSDL

tan2002 1

For SSD < L For SSD > L

headlight beam (diverging from LOS by β degrees)

Sag Vertical Curves

• Assumptions for design– h1 = headlight height = 2.0 ft.

– β = 1 degree

• Simplified Equations

SSD

SSDAL

5.3400

2

A

SSDSSDL

5.34002

For SSD < L For SSD > L

Sag Vertical Curves

• Assuming L > SSD…

SSD

SSDK

5.3400

2

Design Controls for Sag Vertical Curves

from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001

Design Controls for Sag Vertical Curves

fro

m A

AS

HT

O’s

A P

olic

y o

n G

eo

me

tric

De

sig

n o

f H

igh

wa

ys a

nd

Str

ee

ts 2

00

1

Example 1

A car is traveling at 30 mph in the country at night on a wet road through a 150 ft. long sag vertical curve. The entering grade is -2.4 percent and the exiting grade is 4.0 percent. A tree has fallen across the road at approximately the PVT. Assuming the driver cannot see the tree until it is lit by her headlights, is it reasonable to expect the driver to be able to stop before hitting the tree?

Example 2

Similar to Example 1 but for a crest curve.

A car is traveling at 30 mph in the country at night on a wet road through a 150 ft. long crest vertical curve. The entering grade is 3.0 percent and the exiting grade is -3.4 percent. A tree has fallen across the road at approximately the PVT. Is it reasonable to expect the driver to be able to stop before hitting the tree?

Example 3

A roadway is being designed using a 45 mph design speed. One section of the roadway must go up and over a small hill with an entering grade of 3.2 percent and an exiting grade of -2.0 percent. How long must the vertical curve be?

Horizontal Alignment

Horizontal Alignment

• Objective: – Geometry of directional transition to ensure:

• Safety• Comfort

• Primary challenge– Transition between two directions– Horizontal curves

• Fundamentals– Circular curves– Superelevation

Δ

Horizontal Curve Fundamentals

R

T

PC PT

PI

M

E

R

Δ

Δ/2Δ/2

Δ/2

RRD

000,18

180100

2tan

RT

DRL

100

180

L

Horizontal Curve Fundamentals

1

2cos

1RE

2

cos1RM

R

T

PC PT

PI

M

E

R

Δ

Δ/2Δ/2

Δ/2L

Example 4

A horizontal curve is designed with a 1500 ft. radius. The tangent length is 400 ft. and the PT station is 20+00. What are the PI and PT stations?

Superelevation cpfp FFW

cossincossin22

vvs gR

WV

gR

WVWfW

α

α

Fcp

Fcn

Wp

Wn F f

F f

α

Fc

W 1 fte

≈Rv

Superelevation

cossincossin22

vvs gR

WV

gR

WVWfW

tan1tan2

sv

s fgR

Vf

efgR

Vfe s

vs 1

2

efg

VR

sv

2

Selection of e and fs

• Practical limits on superelevation (e)– Climate– Constructability– Adjacent land use

• Side friction factor (fs) variations

– Vehicle speed– Pavement texture– Tire condition

Side Friction Factor

from AASHTO’s A Policy on Geometric Design of Highways and Streets 2004

New Graph

Minimum Radius TablesNew Table

WSDOT Design Side Friction Factors

from

the

200

5 W

SD

OT

Des

ign

Man

ual,

M 2

2-01

New Table

For Open Highways and Ramps