Driving Reaction Time Test
You are driving. Something jumps out. The brake light here is the moment to react, so hit it the instant the road flashes red. Then we do the maths that matters: how many metres your car covers while you are still reacting, before the brakes have done a thing.
Your stopping distance at…
The metres you lose before you brake
Braking feels instant. It is not. Between a hazard appearing and your foot actually pressing the pedal, the car keeps going at full speed, and that gap is pure reaction time. Officials call the distance covered in it your thinking distance, and it scales straight with how fast you are going. At 30 mph you cover about 13 metres a second; at 70, about 31. So the same reaction costs you more than twice the distance on a motorway as it does in town.
That is the point of this test. The reaction itself is the easy part to measure. What makes it matter is turning your milliseconds into metres of tarmac you would never get back. Add the braking distance on top (which grows with the square of your speed) and you can see why speed limits are not arbitrary.
A fair warning about this number
Your score here is a clean reaction to a known signal, so it flatters real driving. On the road you also have to spot the hazard among everything else and decide to brake, which is why driving guides plan for about a second and a half, not a quarter. Treat the distances below as the best case: your alert, undistracted, expecting-it best case. Then imagine adding a phone.