The effect of mental load on driving is discussed. Compensating for difficult or monotonous tasks may require extra effort. It is suggested that while extra effort is a good solution to a short-term problem, in the long term it may involve repetitive activation of the cardiovascular defence response that may lead to hypertension. Methods of measuring mental workload are outlined. Individual differences and driving strategies are discussed. The effects of road edge line marking on mental workload were investigated on rural roads in the Netherlands. Subjects were required to drive differently marked roads in the day and after dark. On centre-lined two-way roads, lateral position of the vehicle was nearer the edge of the road. Driving speed was greater on centre-lined roads than on unmarked roads. Average lateral position on the road was nearer to the centre after dark. Heart rate measurements showed that driving after dark required more effort than daytime driving, especially on unmarked roads. Road marking is therefore beneficial at night but may lead to excessive speed during daylight. Ways of making use of mental workload in road design are discussed, including self explaining roads. These included roads where the edge markings were removed, the road surface roughened to discourage excessive speed, and the speed limit was painted on the road itself. These changes reduced driving speed by 3-4km/h, sufficient to reduce accidents.
Abstract