The object of the investigation was to determine the distribution of brake reaction times (BRT) which an be expected from drivers who have to brake suddenly and completely unexpectedly in traffic situations. The experiments were carried out as follows: 1. A large group of drivers (321) was stopped on the open highway and informed that they would hear a signal for braking within ten kilometres. In this way, a distribution of BRT in a situation where the braking was not completely unexpected, was obtained (BRT). 2. A small group of drivers (5) was tested several times in a similar situation. This provided measures of their BRT. 3. This same small group was also tested several times in situations where the braking signal occurred completely unexpectedly. This provided measures of their BRT in a surprise situation (BRT). 4. The ratio BRT/BRT for the small group was taken as being a correction factor, which could be applied multiplicatively to the BRT values obtained from the large group of drivers and in this way obtain BRT values which could be expected if the situation had been a complete surprise situation. The distribution obtained from the large group after the correction factor had been applied constitutes the main result of the investigation. The corrected median was 0.9 sec. and 25% of the group were estimated to have a BRT longer than 1.2 sec.
Abstract