The science behind automotive stopping distances is simple, in so much that the faster you go, the longer it takes to stop your vehicle. Knowing your stopping times and distances is essential to being a safe driver. However, the time that you need to stop your car does not include the average 1.5 seconds of thinking time to react. In essence, this reaction time has been a hot topic of debate as it is not included in the Highway Code stopping distance and therefore some road safety campaigners argue that the stopping distances given are actually too short.
This 1.5 seconds is the time it takes to spot the hazard and react to it by pressing on the brakes or another appropriate course of action. However, the Department for Transport have stated that the reaction time is 0.67 seconds – this time has been disproved by the charity ‘Brake’.
It’s easy to forget our stopping distances nearly immediately after our theory test (for those who took the theory test!), but it’s essential that we keep this knowledge to stay safe on the roads. In effect, a stopping distance is the result of thinking distance and braking distance. Your thinking distance is how long it takes you, the driver, to react to a hazard the hit the brakes. Your braking distance is how far your vehicle travels when you’ve got your foot right down on the brake – essentially performing an emergency stop. If you check the Highway Code, a car going at 30mph has a 9m thinking distance and a 14m braking distance, resulting in a 23m stopping distance. These stopping distances (obviously) increase the faster your speed.
As you will know, weather and road conditions also drastically affect stopping distances. Environmental factors, specific to a driver that can affect stopping distances are: attention, fatigue, drug/alcohol use, vision complications, driver experience, and hazard perception ability. In terms of the vehicle, it’s age, tyre and brake condition, tyre pressure, weight and safety features all play a part in affecting its stopping distance. Finally, the road surface, gradient, alignment and weather conditions are all environmental factors that can influence a vehicle’s stopping distance…a stopping distance uphill in the dry with a well maintained modern vehicle will be shorter for the exact same speed of travel versus an older car on a wet downhill slope with uneven road surface.
As cars have modernised, it is true that they can now brake more quickly than previous models, however our reaction times have not evolved in the same ways, therefore precautions must always be taken.