Speed effects of automatic camera enforcement on main road 51.

This paper presents a study that looked at changes in vehicle speeds after the installation of automatic speed enforcement on main road 51 (Rasanen, Beilinson & Kallberg 2004). The length of the road section under surveillance was 42.5 km between the cities of Kirkkonummi and Karjaa in Southern Finland. The before-and-after study consisted of spot speed measurements using inductive loops and travel speed measurements using the license plate method. Spot speed measurements were conducted during summer (100 kph) and winter (80 kph) speed limits. Travel speeds were measured only in summer. The study did not consider how effectively the enforcement was conducted. The mean spot speeds decreased at all six measurement points by 1.5-4.4 kph (speed limit 100 kph) immediately after automatic enforcement was introduced. The effect was almost the same a year after the beginning of enforcement (the speeds decreased by 1.1-3.5 kph). All six measurement points showed a similar result also during winter speed limits (the speeds decreased by 1.5-4.9 kph). As a control, speed data from five other measurement points outside the surveillance road section were collected. They did not show the decrease in mean spot speeds. Speed limit excesses of more than 20 kph halved at all surveillance-area measurement spots immediately after automatic enforcement. Again, the effect was almost the same a year after the beginning of enforcement. Correspondingly, speed limit excesses of 11-20 kph decreased at least by a fourth at every measurement point. Speed limit excesses of more than 20 kph during wintertime halved at three measurement points, and at three others decreased by at least by a third. Also during wintertime the proportion of speed limit excesses of 11-20 kph decreased at least by a fourth at every measurement point. However, the proportion of these remained at 10-20% after enforcement during wintertime.uThe mean travel speed decreased by 2.1 kph in the direction of Kirkkonummi but not in the direction of Karjaa. However, the standard deviation of speed was also reduced in the direction of Karjaa. The number of overtakings halved in both directions. For the covering abstract see ITRD E137489.