Braking distance, friction and behaviour

Poul Greibe, July 2007

The recommended braking distances in the Danish Road Standards and Guidelines are in the main based on earlier American findings. In order to beable to assess the validity of the recommended braking distances in relation to contemporary vehicles and motorists in Denmark, the Danish Road Directorate has conducted a study designed to shed light on braking behaviour and braking distances among ordinary (non professional) motorists, at different speeds.

This was done through a measurement programme in which 22 test drivers performed braking manoeuvres at different speeds (80, 110 and 130 km/h). The majority of the test drivers who participated were recruited from among non professional drivers. However, 6 out of the 22 test drivers were professional test drivers with extensive experience in advanced driving technique. Two different recent cars with ABS brakes were used as test cars.

The braking manoeuvres were carried out on dry and wet road on 3 test tracks with different friction. The majority of the manoeuvres performed were emergency stops, in which the test driver was required to bring the vehicle to a complete stand still as quickly as possible.

In addition, a small number of comfort braking manoeuvres were performed in which the test driver was required to bring the vehicle to a comfortable stop.

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