Summary

TRL collaborated with academic partners in the USA and the UK to develop a prediction model for splash and spray, since it is difficult to accurately measure direct splash and spray on highways directly.

594 mm average annual rainfall in London, UK
1,009 mm
average annual rainfall in Washington DC, USA

The challenge

When it’s wet, tyres generate spray on the road, particularly from heavy vehicles. This affects driver visibility, through general spray and waves of water landing on windscreens. It contributes to a small but measurable proportion of accidents. Fine debris containing pollutants is also splattered on vehicles, verges and street furniture. It can create environmental and maintenance problems.

Water on the carriageway can also be a danger by causing hydroplaning and creating excessive light reflection at night, obscuring lane markings. 

Our approach

Two models were developed. The first predicts the depth of water on the highway under different rainfall conditions, whilst the second estimates the creation of splash and spray by commercial vehicles. We also carried out research to understand driver reactions to splash and spray under different circumstances.

We then built a spreadsheet tool to show the propensity for splash and spray, based on input data for road geometry, surface characteristics and the local intensity, duration and frequency of precipitation. 

The results

The tool now helps highway engineers make decisions about the type, priority and effectiveness of maintenance actions. This should increase user satisfaction with the network, lower the number of accidents and reduce the effect of pollutants.

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