On a wet road, how does stopping distance compare to a dry road?

On a wet road, how does stopping distance compare to a dry road?

• A. It is about double the stopping distance of a dry road.
• B. It is the same as on a dry road.
• C. It is half the distance.
• D. It is triple the distance.

Answer: (A)

Wet roads reduce grip, so stopping distances become longer. Stopping distance is made up of thinking distance (your reaction time at a given speed) and braking distance (the distance to stop once you start braking). Your thinking distance doesn’t change much with the road surface, but the braking distance increases on wet surfaces because the tyres have less friction with the wet road. Taken together, at typical speeds the total stopping distance on a wet road is about twice what it would be on a dry road. So the best answer is that stopping distance is about double on a wet road. It can vary with speed, tyre tread, and how much water is on the road, but the rule of thumb is roughly doubling.

Wet roads reduce grip, so stopping distances become longer. Stopping distance is made up of thinking distance (your reaction time at a given speed) and braking distance (the distance to stop once you start braking). Your thinking distance doesn’t change much with the road surface, but the braking distance increases on wet surfaces because the tyres have less friction with the wet road. Taken together, at typical speeds the total stopping distance on a wet road is about twice what it would be on a dry road. So the best answer is that stopping distance is about double on a wet road. It can vary with speed, tyre tread, and how much water is on the road, but the rule of thumb is roughly doubling.