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Switching off traffic signals overnight - Cost-cutting at the expense of safety?
Traffic signals are used at intersections of all kinds wherever this is necessary in order to control traffic flow or to ensure traffic safety. The research carried out to date with respect to traffic safety when traffic signals are switched off at night is no longer up to date and is concerned with the systems installed in West Germany.
Following reunification, many traffic signals in cities of the former GDR were switched off at night, partly as a result of a lack of flexibility in the technical equipment and partly because of the low volumes of traffic. A recent study carried out by the Institute for Traffic Planning and Road Traffic at the Dresden University of Technology  for the German Insurers Accident Research (UDV) demonstrated that switching off traffic signals at night, which is a widespread practice in German cities, cannot be justified on the grounds of safety.
The investigation into the effect of switching off signals at night was carried out in the form of a „with/without“ comparison in the cities of Dresden and Leipzig and the Harburg administrative district. The study compared traffic safety at intersections where the signals were switched off at certain times with traffic safety at comparable intersections where the signals were in operation continuously, taking into account a control group (with the signals in operation).
The data set was made up of accidents with personal injuries over a period of 3 years from 2003 through 2005 and accidents with damage to property from 2005. The total data sample in the survey covered 272 traffic signals, at which 1,855 accidents with personal injuries occurred over 3 years and 3,005 accidents with damage to property occurred in 2005. Of this sample, 182 traffic signals were switched off and 90 operated round the clock.
All the conclusions confirm the effects already established by earlier research.
Switching off traffic signals at night
has a negative impact on road safety
leads to comparatively small energy savings
only reduces travel times by a small amount and hence
only marginally reduces fuel consumption, noise and emissions.
Even though the facts have been known for many years, the option of switching off traffic signals is not merely under discussion: In many cities, the relevant authorities are confronted by demands to switch off a certain percentage of traffic signals at night. As this document has again reliably proved, demands of this sort relating to traffic policy cannot in any way be justified for economic reasons and completely ignore the protection of people and property in our cities.
For this reason, UDV recommends:
Systematic implementation of the stipulations laid down in the General Administrative Regulations on the Road Traffic Regulations (VwV-StVO)
The decision to switch off traffic signals should remain an exception and should be justified and the situation with respect to accidents should be constantly monitored
Improved technology should be used (lowvoltage technology, LEDs)
Intelligent, traffic-dependent signal control methods should be used.