Thinking distance is the distance you travel whilst thinking you need to stop the car and actually hitting the brake. If a child ran out in front of you, there would be a second or two between the time you see them and you braking.
Even if your reaction times are fast, you’ll need to remember that the faster you’re going, the longer it will take you stop. So, if you’re driving at 40mph, your stopping distance will be double what it would be at 20mph, regardless of how quickly you brake.
Braking distance is the distance you travel after having hit the brake pedal. This distance increases the faster you’re going and is also dependent on the weather conditions. If, for example, you’re driving in rain, your stopping distance will be double what it would be on a dry road. When driving on an icy road, what’s more, your stopping distance will be 10 times greater.
Typical stopping distances, as outlined at gov.uk, are:
The two second rule
The two second rule applies to the space you should leave between you and the vehicle in front. You can check that you’ve left a two second gap by choosing a landmark in the road ahead. The vehicle in front should pass that point (e.g. a lamppost) at least two seconds before you do. If you pass the landmark in under two seconds, drop back.
Stopping distances in rain
When the road is wet, your tyres don’t have as much grip on the road surface. Your stopping distance, therefore, will be double what it is in normal driving conditions. Reduce your speed appropriately considering the weather conditions and road that you’re driving on. You should also leave double the space (4 seconds) between you and the vehicle in front.
Stopping distances on icy roads
When driving on icy roads, your stopping distance increases even more dramatically. You should reduce your speed significantly, and leave plenty of space between you and the vehicle in front. Try not to accelerate or brake harshly, as this could cause your vehicle to skid.