Enter the design speed (mph) and the grade (%) into the Stopping Sight Distance Calculator. The calculator will evaluate and display the Stopping Sight Distance. 

Stopping Sight Distance Formula

The following formula is used to calculate the Stopping Sight Distance. 

SSD = 1.47*V*2.5+ (V^2/(30*(.34782+(G/100))))

  • Where SSD is the Stopping Sight Distance (ft)
  • V is the design speed (mph) 
  • G is the grade (%) 

How to Calculate Stopping Sight Distance?

The following example problems outline how to calculate Stopping Sight Distance.

Example Problem #1:

  1. First, determine the design speed (mph). 
    • The design speed (mph) is given as: 50.
  2. Next, determine the grade (%). 
    • The grade (%) is provided as: 15.
  3. Finally, calculate the Stopping Sight Distance using the equation above: 

SSD = 1.47*V*2.5+ (V^2/(30*(.34782+(G/100))))

The values given above are inserted into the equation below and the solution is calculated:

SSD = 1.47*50*2.5+ (50^2/(30*(.34782+(15/100)))) = 351.15 (ft)


Example Problem #2: 

For this problem, the variables needed are provided below:

design speed (mph) = 709

grade (%) = 5

This example problem is a test of your knowledge on the subject. Use the calculator above to check your answer. 

SSD = 1.47*V*2.5+ (V^2/(30*(.34782+(G/100)))) = ?