Research shines light on unlit and foggy motorways

How fog and the transition from lit to unlit sections of road can affect driving performance has been measured in a unique study funded by engineering company Arup and Highways England.

A motorway at night. The vehicle lights are blurry, representing speed.

Drivers need to be able to process visual information effectively, including speed, lane position and hazard awareness when they drive on the motorway. When a person’s vision is impaired by darkness or poor visibility, their ability to drive safely is reduced.

There are currently around 1,917 miles of motorway in England. By understanding where and what type of lighting should be placed along motorways, researchers hope they can improve safety across the network.

To test how driving ability is reduced in dark or foggy conditions and what type of lighting improves visibility, researchers from the School of Architecture Lighting Research Group built a scale model of a three lane motorway with the ability to control the amount and type of light, as well as the presence and density of fog.

Research participants were then asked to ‘drive’ along the motorway and look out for objects which suddenly appear on the road surface or a car ahead moving into their lane. Researchers recorded the reaction times to see how driving performance was affected by changes in lighting and fog.

They found that when driving in thick fog, brighter lighting and lighting with a higher S/P ratio, which appears whiter than the orange sodium lighting more commonly used on UK roads, improved reaction times.

They also discovered that when drivers move from a lit to an unlit section of road, their driving performance immediately decreases and there is no increase in performance over the next 20 minutes when some adaptation might be expected.

The results will feed into Highways England strategy for road lighting, for example, where, when and how much lighting to use.

The project has also paved the way for a securing a £1.2m grant from the Engineering and Physical Sciences Research Council for a project called HAROLD: HAzards, ROad Lighting and Driving.

HAROLD aims to improve drivers’ ability to detect hazards, with a focus on detecting pedestrians, using road lighting and active visibility aids.

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