Safe Stopping Distance – Are Your Brakes Working For You or Against You?
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.
What Factors Influence Stopping Distance?
- Brake condition and type
- Driver attention, alertness and reaction speed
- Vehicle age
- Road surface and condition
- Fatigued drivers
- Road gradient (down-hills are harder to come to a complete stop on)
- Impairment due to alcohol and drugs
- Type and condition of tyres, including tyre pressure
- Road alignment
- Vision issues
- Safety features fitted to the vehicle for example ABS, ESC, EBA, etc.
- Weather conditions
- Driver age and experience
- Vehicle weight
- Hazard perception ability
- Towing a trailer or carrying a heavy load
What is The Standard for Braking Distance?
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:
- original speed of the vehicle
- the type of brake system in use
- the reaction time of the driver/rider and
- the coefficient of friction between its tires and the road surface.
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.