How does it change safety margins if overtaking is prohibited: A pilot study

Overtaking was temporarily prohibited on a 1.2km long stretch of two-lane road and the time headway for every car, passing the site in a certain direction, was measured at two points between which the prohibition sign was posted. Additionally, the lateral position of every car was recorded. Due to the prohibition, some favorable effects on safety margins were found. When passing the prohibition sign the drivers following another car very closely increased their following distance; no such change was found in the control condition. Furthermore, when overtaking prohibited, the closely following drivers reserved a bit greater safety margin with respect to the oncoming vehicles. The results suggest that waiting for an opportunity of overtaking increases the accident risk by inducing very short following distances and driving near the center line. This implies that the total accident loss due to overtaking is not wholly included in the category “overtaking acidents” but, in fact, a part of rear-end accidents should be counted on overtaking, too. This should be taken into account when estimating the pay-off of overtaking on two-lane roads.