STOPPING DISTANCES
(Written by Joel Neilsen, Managing Director, Safe Drive Training)
Many drivers, drive in a false belief that if the car in front suddenly started braking, they would react and brake and end up stopped the same distance apart.
The total stopping distance of a vehicle is made up of 4 components.
- Human Perception Time
- Human Reaction Time
- Vehicle Reaction Time
- Vehicle Braking Capability
The human perception time; is how long the driver takes to see the hazard, and the brain realize it is a hazard requiring an immediate reaction. This perception time can be as long as ¼ to ½ a second.
Once the brain realizes danger, the human reaction time is how long the body takes to move the foot from accelerator to brake pedal. Again this reaction time can vary from ¼ - ¾ of a second.
These first 2 components of stopping distance are human factors and as such can be effected by tiredness, alcohol, fatigue and concentration levels. A perception and reaction time of 3 or 4 seconds is possible. 4 seconds at 100 km/hr means the car travels 110 metres before the brakes are applied.
Once the brake pedal is applied there is the vehicles reaction time which depends on the brake pedal free-play, hydraulic properties of the brake fluid and working order of the braking system.
This is why the tailgating car usually cannot stop, when the brake light came on in the car in front, this driver had already completed the perception, human and vehicle reaction periods. The following driver was perhaps 1 second to late in applying the brakes. At 100km/hr the car required 28 metres further to stop.
The last factor than determines the total stopping distance is the cars braking capability which depends on factors such as;
- the type of braking system,
- brake pad material,
- brake alignment,
- tyre pressures,
- tyre tread and grip,
- vehicle weight,
- suspension system,
- the co-efficient of friction of the road surface,
- wind speed,
- slope of road,
- surface smoothness
- the braking technique applied by the driver.
Worth noting is that from 50 to 100 kph the braking distance of a car will increase from 10 metres to 40 metres. When you double the speed of a car braking distance quadruples.
This is based on the laws of physics. When a car is moving it has kinetic energy, ½mv2. When the velocity doubles the kinetic energy quadruples. The braking capability does not increase when driving faster, there are no reserves of friction. As such in any vehicle when your speed doubles braking distance is four times larger.
BRAKING DISTANCE FROM 90 km/hr and 120 km/hr
Honda Integra GS-R 42 74.4 Audi A4 43.5 80.7 BMW Z3 (2.8) 36.9 64.5 Ferrari 550 Maranello 33.6 59.7 Lexus ES300 42 73.8 Lexus LS400 45.3 78 Mazda MX-5 45.6 76.8 Mazda Protege 47.4 86.1 Mercedes C36 36 63 Mercedes SLK230 Kompressor 36 62.7 Nissan Maxima 42 72.9 Nissan 200SX 38.7 68.4 Saab 9000 Aero 36.6 66.3 Subaru Liberty RX 40.8 70.8 Toyota Camry V6 43.5 82.2 Toyota Corolla 55.8 95.7 Porsche 911 Carrera 4 37.8 66.9
