Describe the factors affecting a driver’s reaction time including drugs…

The idea

Reaction time is the interval between a driver noticing a hazard and beginning to act, for example pressing the brake. It is measured in seconds and forms part of the total stopping distance, which also includes the braking distance. Several factors lengthen reaction time: alcohol and other drugs slow the nervous system and impair judgement; distractions such as a phone conversation, loud music or passengers draw attention away from the road; and tiredness or illness slows responses. Other factors such as speed and road surface affect braking distance rather than reaction time. Poor visibility or a dark road delays the moment a hazard is noticed, so it changes when the reaction interval starts, not how long that interval lasts.

What earns the marks

• Identifies reaction time as the interval between noticing a hazard and starting to respond, such as applying the brakes.
• Names drugs, including alcohol, as a factor that lengthens a driver's reaction time.
• Names distractions, such as using a phone or talking to passengers, as a factor that lengthens reaction time.
• Distinguishes factors that affect reaction time from factors such as speed and road surface that affect braking distance.
• Explains that poor visibility delays when a hazard is noticed rather than lengthening the reaction interval itself.

Common mistakes and how to put them right

• Treats poor visibility as a factor that lengthens reaction time.

  Put it right: Recognise that it delays hazard detection, so the reaction interval begins later.

• Confuses reaction time with braking distance.

  Put it right: Keep reaction time as the time before the driver acts and braking distance as the distance travelled while braking.

• Assumes only drugs affect reaction time.

  Put it right: Include distractions such as phones and passengers as well.

• States that a faster car has a longer reaction time.

  Put it right: Recognise that speed affects stopping distance, not the driver's reaction interval.

Exam tips

• Read the question carefully to check whether it asks about reaction time or stopping distance before choosing an answer.
• Link each named factor to the effect on the driver's nervous system or attention, not to the road or weather.
• Eliminate options that describe braking distance or hazard detection when the question asks specifically about reaction time.