Speed is a critical factor in all road crashes and casualties. Driving is unpredictable and if something unexpected happens on the road ahead – such as a child stepping out from between parked cars – it is a driver’s speed that will determine whether they can stop in time and, if they can’t stop, how hard they will hit.
Reducing and managing traffic speeds is crucial to road safety. Breaking the speed limit or travelling too fast for conditions is recorded (by police at crash scenes) as a contributory factor in the majority of fatal crashes. This is arguably a gross underestimate, because whether or not a vehicle is judged to have been speeding or going too fast for conditions, the fact it was involved in a collision means it was going too fast to have stopped in time. In this way, speed is always a contributory factor, albeit often in combination with other causes: no one was ever killed by a stationary vehicle.
How do we calculate Braking distance? This distance refers to the distance a vehicle will travel from the point where its brakes and brake Pads are fully applied to when it comes to a complete stop. It is affected by the following:
The theoretical braking distance can be found by determining the work required to dissipate the vehicle’s kinetic energy.
The kinetic energy E is given by the formula:
E = (1/2)mv2,
where m is the vehicle’s mass and v is its speed.
The work W done by braking is given by:
W = μmgd,
where μ is the coefficient of friction between the road surface and the tires, g is the gravity of Earth, and d is the distance travelled.
The braking distance (which is commonly measured as the skid length) given an initial driving speed v is then found by putting W = E, from which it follows that
d = v2/(2μg).
The maximum speed given an available braking distance d is given by:
v = √(2μgd).
Note that these theoretical formulas do not take account of the driver’s reaction time (an example is the two-second rule).
[Info from Wikipedia] and excerpted from ArriveAlive.