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CHAPTER 2

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CHAPTER 2

Horizontal alignment design

Vertical alignment design

At-grade intersection design

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Reduce the number of serious andpotential accident.

Ensure the ability to bear the hightraffic load.

Minimize traffic and vehicle

delays. Construction of roads with

environment consideration.

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DEFINATION

Distance along the highway in which

there is an obstacles object at a certainheight can be seen by drivers on anongoing basis.

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Sight Distance need to be provided, sothat:

Driver can stop safely when bumped intoan unexpected obstacle.

Help driver to pass other vehicles safely.

Give drivers an opportunity to takeappropriate action at a complex roadintersections.

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There are three types of sight distance :

Stopping sight distance

Passing sight distance

Decision sight distance

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The distance required by the driver fromTIME PERCEPTION, REACTION and

BRAKING, that needed by a vehicle that ismoving at or near the design speed to stopsafely without crashing unexpectedobstacle in the path or something thatappears suddenly.

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STOPPING SIGHT DISTANCE, d1

d1 = dt + db

TOTAL REACTION TIME, dt

dt = time preception + reaction

= 0.278 tV

t = reaction time (seconds)

V =speed design (km/j)

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BRAKING TIME, db

db = total distance need after braking actions made

depending on vehicle early speed and friction

between tyres and the road surface.= V / ( 254f ) @ v / ( 2fg )

V =speed design (km/j)

v = speed design (m/s)g = acceleration gravity (9.81 m/s)

f = friction between tyres and road

surface

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Hence;

STOPPING SIGHT DISTANCE, d1

d1 = dt + dbd1 = 0.278 tV + V / ( 254f )

@

0.278 tV + v / ( 2fg )

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Effect of SLOPE/GRADIENT in STOPPING SIGHTDISTANCE.

UP THE SLOPE

db = V / 254 (f + G )@

= v / 254 (fg + G )

V =speed design (km/j)v = speed design (m/s)

f = friction between tyres and road surface

G = Gradient value

g = acceleration gravity (9.81 m/s)

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DOWN THE SLOPE

db = V / 254 (f - G )

@

= v / 254 (fg - G )

V =speed design (km/j)

v = speed design (m/s)

f = friction between tyres and road surface

G = Gradient value

g = acceleration gravity (9.81 m/s)

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The shortest distance required to exit thenext speeding to its original lane

overtaking him, and then came back intothe original lane safely and not interferewith vehicle from front or vehicles thathave been overtake.

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Ideally, the driver wishes the highway is straightand flat, but there are some disadvantages. Hard to fit with the natural topography of the

land involves a lot of work . In terms of humanity, going straight tedious

and debilitating

Irradiation headlight disrupt oncoming driversat night.

Hard to predict the speed of other car. Risky toovertake.

Tend to speed

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Highway Council Malaysia standard doesnot encourage the use of long straight drive

continuously for more than 2 minutes . For example, if the speed design 100km/j,

hence the maximum straight road is := 100 km/j x 2min x (1hour/60min)

= 3.33 km

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Design based on appropriate relationshipbetween design speed and curvature andtheir interaction with side friction andsuper-elevation.

Along circular path, inertia causes the

vehicle to attempt to continue in a straightline.

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Super-elevation and friction between tireand roadway provides a force to offset the

vehicles inertia; this force is directedtoward the center of curvature. Horizontal Alignment consist of:

Tangents

Curves

Transitions

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TYPES OF CIRCULAR CURVES:

simple circular curve

compound curve

reverse curve

Spiral curve

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