How this calculator works
During reaction delay the vehicle travels at its initial speed. Constant net deceleration then removes its speed over a braking distance proportional to speed squared. In friction mode the road slope changes both the normal load and the downhill gravity component. Friction is entered explicitly because wet or dry labels cannot determine a reliable value. The model is educational and omits changing grip, brake fade, wind and driver behaviour.
Formula
dreaction = vt; dbrake = v²/(2a); tbrake = v/a. For grade q = tan(theta), a = g(mu cos(theta)+sin(theta)).
Worked example
At 20 m/s, 1.5 s reaction delay and 5 m/s² braking deceleration, reaction distance is 30 m and braking distance is 40 m, for 70 m total.
Advertisement
Frequently asked questions
Does doubling speed double stopping distance?
Reaction distance doubles, but braking distance becomes four times as large when deceleration stays fixed.
Which sign represents downhill?
Enter negative grade for downhill. A -5% grade is -5 in the percent display.
Can the calculator establish a safe following distance?
No. Real conditions and unexpected events require allowances beyond this constant-deceleration estimate.