TRL research reveals causes of glare from vehicle lights

A study conducted by TRL has revealed measurable on-road effects caused by bright headlamps and highlights.

The Department for Transport (DfT) commissioned the research, which combined real-world data collection with a national driver survey conducted through the RAC Driver Opinion Panel.

TRL’s report offers new insights into how vehicle lighting and road conditions contribute to the experience of glare.

More than half of UK drivers indicated that they have either reduced or completely stopped driving at night, or would do so if possible, due to the brightness of headlamps.

Many drivers perceive modern vehicle headlights as too bright, particularly those that emit a whiter light or are installed on taller vehicles such as SUVs.

An analysis of over 50 hours of on-road testing, using a car equipped with a luminance camera and other sensors, demonstrated a strong correlation between higher luminance levels and the glare experienced by occupants.

The study also found that the likelihood of experiencing glare increases depending on the type of vehicle, the geometry of the road, as well as the pitch and roll of the vehicle being driven.

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What can be done to help with headlight glare in the UK?

In its report, TRL recommends several actions for both government and industry to carry out to tackle the issue of headlight glare.

These include establishing regular national surveys to track trends in drivers’ experiences with glare.

It also suggests launching public information campaigns to raise awareness about the risks of glare and to offer practical advice for making night driving less stressful.

Further research is encouraged into vehicle design elements such as the use of novel LED headlamps and the impact of vehicle height.

Finally, the report advocates for a review and update of vehicle lighting standards to better reflect real-world driving conditions, proposing a shift in regulatory focus from luminous intensity to luminance.

Dr Shaun Helman, who led the research at TRL, said: “This research provides compelling evidence that glare from vehicle lighting is a genuine issue for UK drivers, and can be measured in real driving conditions.

“By combining scientific measurement with driver perspectives, we now have a clearer understanding of the conditions under which glare occurs and the factors that contribute to it. These objective findings are a first step to take glare from anecdotal complaints into the realm of scientific evaluation.

“Continued research will help inform UK road safety and transport policy. The long-term goal is to improve public confidence and safety when driving at night.”

RAC senior policy officer Rod Dennis said: “Having campaigned hard for this study, we welcome its findings which independently confirm what drivers have been telling us – that rather than being an imagined phenomenon, some bright headlights do cause a glare problem. 

"While drivers clearly benefit from high-performing headlights, it’s important this doesn’t lead to others suffering the effects of dazzle, so a balance needs to be struck.

“We don’t yet have all the answers, but this report undoubtedly helps moves us towards tackling the complex problem of glare from vehicle headlights. It’s vital the report and its considerations are now reviewed carefully to put us on a path towards changes that ultimately benefit all road users.”