Fact

Lighting - What is the road safety effect of (partially) switching off public lighting on motorways?

In general, a reduction of the illuminance level on motorways results in a decrease in road safety. The effect on road safety does, however, depend on the degree of the reduction of the illuminance level and the road circumstances, such as traffic flow and the complexity of the road design. Therefore, there is no consensus about the impact of (partially) switching off public lighting on motorways.

For environmental reasons and in order to save energy costs, public lighting in the Netherlands is sometimes dimmed or switched off (see for example [22] [23] [24] ). Thus, lighting on urban ringroads, motorways with high traffic flow, or roads that were sub-optimally designed is dimmed from 11 pm to 5 am, whereas it is completely switched off on other motorways.

An international meta-analysis of accidents in different illuminance conditions, shows that a 50% reduction of the illuminance level, by switching off every other lamp post along (mostly) motorways, involves a 17% increase of the injury crashes and a 27% increase in the number of crashes resulting in material damage only [2]. However, a study by Rijkswaterstaat (Directorate for Public Works and Water Management) shows that completely switching off public lighting on Dutch motorways with a low traffic flow and a safe road design hardly affects road safety [25] [26]. This research result is remarkable in the light of the international meta-analysis: according to the researchers, the negative consequences of switching off public lighting depend on the traffic flow along the road section. If the traffic flow is very low, switching off public lighting does not have any negative consequences for road safety. Martens [23] reports that switching off every other lamp post on provincial roads (with the exception of intersections and roundabouts) does not have any negative consequences for driving behaviour, perceived safety and subjective workload. In this study, the effect of switching off every other lamp post on the accident risk is not discussed.

In this field of study, dynamic public lighting is a familiar concept. Dimmable public lighting, for example, offers the possibility to vary between two or more illuminance levels depending on traffic or weather circumstances. In a Dutch study, this form of dynamic public lighting and its effect on driving behaviour, perception and acceptance has been examined [27]. It may be concluded that, in favourable circumstances (low traffic flow, dry weather) a much lower level of illuminance, viz 20% of the normal level, will not lead to any problems

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31 Jul 2018

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