Stopping Sight Distance | Overview and Calculation

Stopping Sight Distance (SSD) is the minimum sight distance for the driver to stop without colliding at any point of the highway.

Sight Distance is the length of road which is visible to the driver at any instant. If we are driving at 80 kmph, and suddenly we see a pedestrian crossing, we should be able to see them before so that we are able to react and brake without colliding. This distance is known as stopping sight distance)


It can be formally defined as the minimum sight distance for the driver to stop without colliding at any point of the highway. It depends on 

  • Total reaction time of the driver

  • Speed of vehicle

  • Efficiency of brakes

  • Gradient of road

  • Friction

For two way traffic traffic without median - 2 times SSD is the stopping the sight distance

Total reaction time of driver

Perception time (We realise that we have to stop) and Brake reaction time (Time to apply the brakes)

PIEV Theory

  • Perception - Sensation received by brain

  • Intellection - Understanding the situation (that you have to apply the brakes)

  • Emotion - Feelings (like fear, sad)

  • Volition - Time taken for final action (applying the brakes)

Stopping Sight Distance Calculation

  • Kinetic energy is equated to the work done to apply the brakes - Braking distance

  • Reaction time varies. For young drivers it can be 1-2 sec and older drivers it can be as high as 3-4 seconds.

  • SSD will be more when you are going downhill (downward slope). Use minus n/100 in formula. For upward slope, use +n/100.

  • Friction coefficient varies from 0.3-0.4

SSD Formula

  • Facebook
  • Twitter
  • YouTube
  • Instagram


APSEd is an E-learning platform for Civil Engineering by IIT-B Graduates. Get access to all in one place!

  • Video Lectures & Study Material

  • Practice Questions & Mock Tests

  • Exclusive Doubt Support

600+ learners are studying with us. Join them and learn with us for an optimized learning experience. 

APSEd Founders

Hi! I am Aditya, co-founded APSEd with Palaniappan.


Our brain can accumulate and memorize things to a certain extent. Once it is overloaded, some of the facts and formulas you remembered fade away over time.


All this becomes easier once we understand the concept and know how to apply them. This is what we strive to achieve through our courses. 

Our Courses + Your Effort = Success in exams!


Join Us!