Definition of Sight distance | Stopping and passing sight distance

Tuesday, May 14, 2013 19:46
Posted in category Transportation Engineering
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Sight distance

The clear distance ahead of vehicle which is visible to the driver is known as sight distance.

If suitable sight distance is not provided on the curves, then highway become accidential spot.

There are two types of sight distances:

  1. Stopping sight distance.
  2. Passing sight distance.

Stopping sight distance

The minimum distance within which a driver can safely stop his vehicle without any collision with some vehicle, animal or any other object is known as stopping sight distance.

It consists of two types of distances:

Decision distance and decision time

The distance covered by the vehicle prior to the application of brakes (but the obstruction is visualized) is known as decision distance.

The time taken to cover this distance is known as decision time or recognization time. During decision time, the vehicle will move with the same velocity. It depends upon:

  1. Physical fitness of the driver i.e eyesight.

  2. Alertness of the driver.

  3. Mental health of the driver.

Braking distance and braking time

The distance travelled by the vehicle after the application of brakes, is known as braking distance. Time required for this distance is known as braking time.

Braking time depends upon:

  1. Friction between tyres and road surface.
  2. Condition of the tyre and road.
  3. Velocity of the vehicle.
  4. Condition of the brakes of the vehicle.

So Stopping sight distance = Decision distance + Braking distance

Passing sight distance

The minimum distance ahead of the vehicle which is necessary to be clear for the safe passing is known as passing sight distance.

In this case, over taking vehicle move towards right of the over taken vehicle. And then after over taking comes to its original lane.

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