Speed and Stopping Distances Flashcards
6 cards from real DVSA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Speed and Stopping Distances flashcards as text
In a typical emergency stop at 30 mph, roughly how many car lengths does it take to stop?
Answer: 6 car lengths
At 30 mph, the overall stopping distance of 23 metres is roughly equivalent to 6 car lengths (with an average car length of about 4 metres). Visualising stopping distances in car lengths helps you judge whether you have enough space.
What is the purpose of engine braking (using a lower gear) when descending a steep hill?
Answer: To assist the brakes and prevent them from overheating, which would increase stopping distance
Engine braking uses the engine's compression to slow the vehicle, reducing the load on your foot brakes. On long descents, continuous braking can cause brake fade — where the brakes overheat and become less effective, dramatically increasing stopping distance. Select a lower gear before the descent.
How does a wet road surface specifically affect braking distance compared to thinking distance?
Answer: It primarily increases braking distance because of reduced tyre grip, while thinking distance remains the same
Wet roads primarily affect braking distance by reducing the friction between tyres and the road surface. Thinking distance is not directly affected by road conditions — it depends on the driver's alertness and reaction time. However, the overall stopping distance increases significantly because the braking component doubles or more.
What is the recommended minimum following distance in heavy rain on a motorway?
Answer: At least double the normal gap (4 seconds)
In heavy rain, you should at least double your following distance to a minimum of 4 seconds. On motorways, where speeds are higher, this becomes even more critical because spray from vehicles ahead can severely reduce visibility and stopping distances are much longer.
A driver is travelling at 70 mph and is distracted by a mobile phone. How might this affect their stopping distance?
Answer: Their thinking distance could increase significantly because their reaction time is impaired, adding many metres to the overall stopping distance
Mobile phone distraction can add 0.5 to 1.5 seconds to reaction time. At 70 mph, each additional second of thinking time adds roughly 31 metres (about 100 feet) to the stopping distance. A distracted driver at 70 mph could need an additional 15-46 metres compared to an alert driver.
Why does the Highway Code use specific stopping distances for each speed rather than a simple formula?
Answer: Because braking distance does not increase linearly with speed — it increases with the square of speed, making simple rules misleading
Braking distance increases with the square of speed (a physics principle related to kinetic energy). This means the relationship is not proportional — doubling speed quadruples braking distance. Providing specific figures for each speed helps drivers understand that higher speeds require disproportionately more stopping room.