1.12 - Reaction Times

Reaction time and the factors that affect it

• Reaction time is how long a person takes to respond to an event - for example, seeing a hazard and braking.
• A typical human reaction time is between 0.2 s and 0.9 s.

Factors that increase reaction time

• Tiredness
• Drugs
• Alcohol
• Distractions (such as using a mobile phone or talking to passengers)

Reaction time and driving

• An alert driver's reaction time in a real driving situation is around 1 s.
• The longer the reaction time, the further the vehicle travels before the driver reacts, which increases the thinking distance.

Measuring reaction times with the ruler drop test

• Reaction times are so short that a stopwatch can't measure them accurately.
• Two common methods:
  1. A computer-based test (e.g. clicking a mouse when a screen changes colour).
  2. The ruler drop test.

Method - Ruler drop test

1. Sit with your forearm resting on the edge of a table. Another person holds a ruler vertically between your thumb and forefinger, lined up with the zero mark.
2. Without warning, the person drops the ruler. You catch it between your thumb and finger as quickly as possible.
3. Read the distance on the ruler at the top of the thumb. The greater this catch distance, the longer the reaction time.

Improving the quality of the results

• Repeat the test multiple times, discard anomalies, and calculate a mean catch distance.
• Keep control variables the same each time (same ruler, same drop height, same person dropping it).