Increase of Traffic Safety by Surveillance of Speed Limits with Automatic Radar-Devices on a Dangerous Section of a German Autobahn: A Long-Term Investigation


Summary Information

This study (1971-1983) evaluated the permanence of safety benefits achieved through automated speed enforcement on the Autobahn (A3) at Elzer Mountain in Germany. In order to improve drivers' ability to estimate proper speed and to reduce excessive numbers of annual fatalities police introduced speed limit restrictions, heightened police enforcement (especially on weekends), and installed automatic radar detectors and speed cameras.

In 1971, a "before" investigation showed that 80 to 95 percent of passenger cars and 15 percent of trucks exceeded the recommneded roadway design speed at Elzer Mountain. In this year, personal injury rates were about 4.5 times higher in the downhill direction (5 percent negative grade) as compared to the uphill direction, and the most frequent and severest accidents were the result of rear-end collisons caused by trucks.

In 1972, a 100-kilometer per hour (km/hr) speed limit was imposed on passenger vehicles in the left and middle lanes, and a 40-km/hr speed limit was imposed on vehicles in the right lane (truck lane). In addition, a DO-NOT-PASS sign was posted for trucks.

Approximately one year later automatic photo radar units were installed. Passenger cars exceeding 110-km/h, and trucks exceeding 45-km/h were photographed and tickets were sent to the owners by mail.


Immediately after the100-km/h speed limit restriction was imposed, a 30-km/h reduction in mean speed was noted. Following installation of the speed cameras, an additional 20-km/h reduction in speed occurred. The combined effects of the speed limit and speed cameras produced a 91 percent reduction in accidents in the study area.

By 1982 the reduced accident rate and lower speeds were deemed sustainable. In 1981 only 7 percent of cars in the left lane, 3 percent of cars in the middle lane, and 10 percent of vehicles in the right lane (trucks) were detected by the photo radar units at speeds greater than 110-km/h for cars or 45-km/h for trucks.

Overall, the accident rates between 1971 and 1982 decreased by a ratio of 18:1. In addition, the seven or eight fatalities per year observed on the downgrade section of roadway in 1972 were reduced to one fatality per year through the early 1980’s. In addition, the accident rate between the upgrade and downgrade sections of autobahn were not significantly different at the time this study was published in 1984.


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Increase of Traffic Safety by Surveillance of Speed Limits with Automatic Radar-Devices on a Dangerous Section of a German Autobahn: A Long-Term Investigation

Author: Lamm, R. and J. Kloeckner

Published By: Transportation Research Board

Source Date: 1984

Other Reference Number: TRR 974


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Goal Areas



photo enforcement, speed cameras, automated speed enforcement, automated enforcement, photo radar

Benefit ID: 2002-00236