Road

Widening Of Curves

Island

Freeway Entrance and Exit

Types of Interchanges

Highway Intersection

Widening Of Curves

Reasons:

1. To force the drivers to shy away from the pavement edge.

2. To increase the effective transverse vehicle width for non- tracking of front and rear wheels.

3. To give additional width due to the slanted position of front wheel to the roadway center line.

4. For 7.20 meters wide roadway, an additional width of 30 centimeters is necessary on an-open curve highway.

Island

-an island is a defined area between traffic lanes for control of vehicle movement and for pedestrian refuge.

-on at-grade intersection in which traffic is directed into definite paths by island is termed as channelized intersections.

Purposes:

1. Separation of vehicular flows.2. Separation of conflicts.3. Reduction of excessive pavement areas.4. Reduction of traffic and indications of proper use of

intersections.5. Arrangement to favor a prominent turning movement.6. Location of traffic control devices.

Prohibited turns maybe prevented

Funneling vehicles into narrowing opening prevent overtaking and passing conflict area.

Refuge provided for turningVehicles.

The angle between intersecting streams of traffic can be smooth and favorable.

Speed of vehicle controlledOver approaching intersections.

The type and form of freeway interchanges requires selection of the conformation that is best suited to a particular situation and demand.

The functions of freeway interchanges are:1. To provide separation between two or more traffic arteries.2. To facilitate the easy transfer of vehicles from one entry to

the other or between local roadway and the freeway .

Types of Interchanges

Types Of

Freeway Interchanges

Diamond interchanges

The simplest and lowest cost form of interchange. It is Recommended where the freeway crosses non-freeway arterial.

Clover leaf

Partial cloverleaf

The cloverleaf type of interchange is recommended for freeway and arterial intersection. Intersecting arteries are separated and free of intersections.

Objection to the cloverleaf interchange design

1. It requires large area of land.

2. At higher design speed, more time is consumed just to traverse the longer loops.

3. Vehicle making left turn execute 270 degree right turn and travel greater distance becoming very unpleasant and hazardous due to the sharp curves and steep grades.

4. Vehicle leaving the curve loop in one quadrant weave those entering the adjacent loop from the through roadway

T- or Trumpet

Under this type, weaving and merging movements are separated. It also provide an opportunity to speed adjustment clear of the freeway.

when freeway meets freeway where traffic movement is heavy, interchange is provided with directional turn in all four quadrants.

Channelized Interchanges

Fully Directional Interchanges

Roadway at four levels is appropriate where land is very expensive. And is more open design common in 3 level of roadways required to meet control or grades and slight distance.

Highway Intersection at Grade

All highways except freeways have intersections at grade. Intersectionarea is considered part of every connecting roads. In this area all crossing and turning movement occur.

1. For right angle intersections with little traffic, the use of street sigh is more than sufficient.

2. For Y intersection or other related conformation where vehicles meet at unfavorable angles may require channelization.

3. The flared design will involve the following:a. widening he entering traffic lane to allow deceleration of the car

and clear of to traffic.b. widening the leaving lanes to provide acceleration and merging

from the traffic streams. 4. Intersections must accommodate large trucks, and the radius of all

curves must be sufficient enough to accommodate them.

5. A careful traffic count and projected future improvement must precede the design of all critical sections. Based from the data gathered on traffic count, the lane capacity could determined including the number of lanes to be constructed.

Interchange At

Grade

Flared type

Channelized - y

Channelized-y

Y-turning Roadways

Unchannelized-T

T – with turning

roadway

4 leg channelized type intersection

Parrallel

type

Rotary intersection Round about

Multi-leg intersection

unchannelized

Freeway Entrance and Exit

The over all effectiveness of the individual freeway systems is governed by the flow characteristics of vehicles, and the driver’s behavior near on and off the channel.

A single lane on ramp vehicle flows into the outer continuing freeway lane. The design is either a taper blending into the through lane or an auxiliary lane parallel to the through the lane. In either case, sufficient length is required to allow the vehicles to accelerate and merge into the ongoing vehicle stream at speed near that of the freeway.

Vehicles leaving the freeway need distance to accelerate and clear of the flow of ongoing traffic. In situation where one lane could not meet the traffic demand, two lane exist is necessary . In that situation, an auxiliary lane must be added to the freeway at least 800 meters before the point of exit. Even with one lane exist, an auxiliary lane is necessary for it reduces confusion and congestions.

Freeway speed Km/hr

On Ramp or Off Ramp Design Speed km/hr

Stop 20 30 40 50

L= Length of Ramps in Meter

On ramp 80 95

110

228 189 150 48 51350 321 273 177 51477 450 400 303 1774

Off Ramps80 95

110

130 115 95 68 ----159 147 129 102 72185 170 153 129 102

Sampling of Minimum For Freeway on and off the Ramps

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