Braking Distance Calculator

Braking Distance is evaluated from Initial Speed, Reaction Time and Road / Brake Condition. The calculation reports Reaction Distance, Braking Distance and Total Stopping Distance.

Results

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About the Braking Distance Calculator

Braking Distance is treated here as a quantitative relation between Initial Speed, Reaction Time and Road / Brake Condition and Reaction Distance, Braking Distance, Total Stopping Distance and Total Stopping Distance.

The calculator uses a multi formula configuration. Each reported value is read as a direct evaluation of the stored rules with the declared field formats and units.

Formula basis:
v_fps = mph x 1.4667 (unit conversion: 1 mph = 1.4667 ft/sec)
Reaction distance (ft) = v_fps x reaction_time
Braking distance (ft) = v_fps^2 / (2 x mu x g) where g = 32.174 ft/s^2
Total stopping distance = reaction distance + braking distance

Interpret the outputs in the order shown by the result fields. Optional inputs affect only the outputs that depend on those variables.

Formula & How It Works

The calculation applies the following relations exactly as recorded in the metadata:

v_fps = mph x 1.4667 (unit conversion: 1 mph = 1.4667 ft/sec)
Reaction distance (ft) = v_fps x reaction_time
Braking distance (ft) = v_fps^2 / (2 x mu x g) where g = 32.174 ft/s^2
Total stopping distance = reaction distance + braking distance

Each output field is produced by substituting the supplied inputs into the relevant relation and then applying the declared rounding or text format.

Worked Examples

Example 1: Highway driving at 65 mph, average driver, dry road

Inputs

speed: 65 react_time: 1.0 sec (alert driver) road_cond: Dry pavement, good brakes (0.85g)
Reaction Distance: 95 ft. Braking Distance: 166 ft. Total Stopping Distance: 262 ft. Total Stopping Distance: 17.4 car lengths

With Initial Speed = 65, Reaction Time = 1.0 sec (alert driver) and Road / Brake Condition = Dry pavement, good brakes (0.85g) as the stated inputs, the result is Reaction Distance = 95 ft, Braking Distance = 166 ft and Total Stopping Distance = 262 ft. Each value corresponds to the declared output fields.

Example 2: School zone 25 mph, distracted driver (2.0 sec reaction), wet road

Inputs

speed: 25 react_time: 2.0 sec (distracted/impaired) road_cond: Wet pavement, good brakes (0.60g)
Reaction Distance: 73 ft. Braking Distance: 35 ft. Total Stopping Distance: 108 ft. Total Stopping Distance: 7.2 car lengths

With Initial Speed = 25, Reaction Time = 2.0 sec (distracted/impaired) and Road / Brake Condition = Wet pavement, good brakes (0.60g) as the stated inputs, the result is Reaction Distance = 73 ft, Braking Distance = 35 ft and Total Stopping Distance = 108 ft. Each value corresponds to the declared output fields.

Example 3: Interstate highway 75 mph, expert driver, dry pavement

Inputs

speed: 75 react_time: 0.75 sec (expert driver) road_cond: Dry pavement, good brakes (0.85g)
Reaction Distance: 83 ft. Braking Distance: 221 ft. Total Stopping Distance: 304 ft. Total Stopping Distance: 20.2 car lengths

With Initial Speed = 75, Reaction Time = 0.75 sec (expert driver) and Road / Brake Condition = Dry pavement, good brakes (0.85g) as the stated inputs, the result is Reaction Distance = 83 ft, Braking Distance = 221 ft and Total Stopping Distance = 304 ft. Each value corresponds to the declared output fields.

Example 4: Winter driving at 35 mph on glare ice

Inputs

speed: 35 react_time: 1.5 sec (average driver) road_cond: Ice — glare ice (0.15g)
Reaction Distance: 77 ft. Braking Distance: 273 ft. Total Stopping Distance: 350 ft. Total Stopping Distance: 23.3 car lengths

With Initial Speed = 35, Reaction Time = 1.5 sec (average driver) and Road / Brake Condition = Ice - glare ice (0.15g) as the stated inputs, the result is Reaction Distance = 77 ft, Braking Distance = 273 ft and Total Stopping Distance = 350 ft. Each value corresponds to the declared output fields.

Common Use Cases

  • Calculate stopping distance at highway speeds
  • Compare stopping distance with different reaction times
  • Understand how speed affects braking distance