Stopping Distance Calculator
Stopping distance is the total distance a vehicle travels from the moment a hazard is perceived until the vehicle comes to a complete stop. It comprises two parts: reaction distance (traveled during the driver's reaction time) and braking distance (traveled while decelerating). Understanding stopping distance is essential for safe driving and road design.
The total stopping distance of a vehicle depends on two phases. During the reaction phase, the car continues at its current speed while the driver perceives the hazard and moves their foot to the brake. The reaction distance equals speed multiplied by reaction time: dreaction = v × treaction.
During the braking phase, kinetic energy is converted into heat through friction between the tires and road surface. The braking distance is derived from kinematics: dbraking = v² / (2μg), where μ is the coefficient of friction and g = 9.81 m/s². On dry asphalt, μ ≈ 0.7, but on wet roads it drops to about 0.4, and on ice it can be as low as 0.1.
Because braking distance grows with the square of speed, doubling your speed quadruples the braking distance. At 60 km/h on a dry road the total stopping distance is roughly 36 m, but at 120 km/h it jumps to about 118 m. This is why speed limits exist and why keeping a safe following distance is critical, especially in adverse weather conditions.