Evaluate the effect of various factors on thinking distance based on given…

The idea

Thinking distance is the distance a vehicle travels during the driver's reaction time, before the brakes are applied. It equals speed multiplied by reaction time, so at a given reaction time a higher speed produces a proportionally greater thinking distance. Given data, you should identify the factor being varied, such as speed, reaction time, tiredness, alcohol or distraction, and judge how it changes thinking distance. For example, if a driver's reaction time doubles while speed stays constant, thinking distance doubles. If speed doubles at constant reaction time, thinking distance also doubles. Evaluating means using the data to support a conclusion, recognising trends and commenting on the reliability or limitations of the evidence.

What earns the marks

• State that thinking distance is the distance travelled during the driver's reaction time and is calculated as speed multiplied by reaction time.
• Use given data to show that thinking distance increases when speed increases at constant reaction time, and increases when reaction time increases at constant speed.
• Identify factors that increase reaction time, such as tiredness, alcohol, drugs, distraction or illness, and link each to a longer thinking distance.
• Evaluate the quality of the data by commenting on whether repeats were taken, whether the trend is consistent and whether other variables such as road or vehicle conditions were controlled.
• Draw a conclusion that is supported by the figures, for example comparing two drivers or two speeds and stating which has the greater thinking distance and by what factor.

Common mistakes and how to put them right

• Confusing thinking distance with braking distance or stopping distance.

  Put it right: Thinking distance occurs before the brakes act, braking distance occurs while braking, and stopping distance is the sum of the two.

• Assuming that a factor such as alcohol affects braking distance directly.

  Put it right: Alcohol mainly increases reaction time, so it increases thinking distance; braking distance depends on speed, mass and road conditions.

• Describing a trend without using the data, for example saying 'faster means further' without quoting values.

  Put it right: Support each statement with figures from the table or graph.

Exam tips

• Quote numerical values from the data when comparing thinking distances, and state the factor by which one value is larger where possible.
• Link each named factor to the mechanism: it changes reaction time, which changes thinking distance at a given speed.
• If asked to evaluate, include both a strength and a limitation of the data, such as a clear trend but few repeats or uncontrolled conditions.