If the brakeefficiency is 100 the vehicle will stop the moment the brakes are

If the brakeefficiency is 100 the vehicle will stop

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The efficiency of the brakes depends upon the age of the vehicle, vehicle characteristics etc. If the brakeefficiency is 100%, the vehicle will stop the moment the brakes are applied. But practically, it is notpossible to achieve 100% brake efficiency. Therefore the sight distance required will be more when theefficiency of brakes are less. Also for safe geometric design, we assume that the vehicles have only 50%brake efficiency. Frictional resistance between the tyre and the road The frictional resistance between the tyre and road plays an important role to bring the vehicle to stop.When the frictional resistance is more, the vehicles stop immediately. Thus sight required will be less. Noseparate provision for brake efficiency is provided while computing the sight distance. This is taken intoaccount along with the factor of longitudinal friction. IRC has specified the value of longitudinal frictionin between 0.35 to 0.4. Gradient of the road. Gradient of the road also affects the sight distance. While climbing up a gradient, the vehicle can stopimmediately. Therefore sight distance required is less. While descending a gradient, gravity also comesinto action and more time will be required to stop the vehicle. Sight distance required will be more inthis case. Stopping sight distance Stopping sight distance (SSD) is the minimum sight distance available on a highway at any spot having sufficient length to enable the driver to stop a vehicle traveling at design speed, safely without collision with any other obstruction. There is a term called safe stopping distance and is one of the important measures in traffic engineering. It is the distance a vehicle travels from the point at which a situation is first perceived to the time the deceleration is complete. Drivers must have adequate time if they are to suddenly respond to a situation. Thus in highway design, sight distance atleast equal to the safe stopping distance should be provided. The stopping sight distance is the sum of lag distance and
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Dept. Of Civil Engg, SJBIT Page 19
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  • Summer '12
  • Sarkarbabu
  • Civil Engineering, Friction, Road transport, Stopping sight distance, HIGHWAY GEOMETRIC DESIGN, horizontal curve, Dept. of Civil Engg

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