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The object of this investigation was to determine the distribution of brake reaction times which can be expected from drivers who have to brake suddenly and completely unexpectedly in traffic situations. The experiments were carried out as follows: 1. Brake reaction time was measured on a large group of drivers (321), in an anticipated situation on the road (Brake reaction time 1). 2. A small group of drivers (5) was repeatedly tested in the same way (Brake reaction time 2). 3. The same small group was repeatedly tested in a surprise situation (Brake reaction time 3). 4. The ratio of brake reaction time 3 to brake reaction time 2 was used as a correction factor and applied to brake reaction time 1. The corrected median of the resulting distribution was 0.9 sec.; 25% of the group was estimated to have a brake reaction time longer than 1.2 sec.
Johansson et al. (Mon,) studied this question.