An online tool that has shown which London roads are most likely to cause river pollution, is expanding to assess risk from agricultural areas.

The Road Pollution Solutions Tool is the first of its kind, and was developed by the British Geographical Survey with partners including environmental charities Thames21, South East Rivers Trust and Middlesex University. Using data to predict which of the city’s roads create the most run-off pollutants, the platform tells users how the pollution can be tackled with sustainable, nature-led projects.

The aim is to help local authorities prioritise water-quality improvement interventions at roads where major road run-off is occurring and in the green spaces that lie between the roads and the rivers. Launched in London in 2023, the tool is now being expanded to analyse the Upper Thames catchment, above Dorchester-on-Thames, where pollutants including fertilisers and pesticides end up into rivers from agricultural land.

The catchment is predominantly covered by arable crops and grassland, but it has varied geology and soils that affect the movement of water and pollutants through the landscape. It also includes urban areas and sections of the M4 and M40 motorways, which generate pollution in road run-off.

John Bryden, head of improving rivers at Thames21, said: “There are more than 300 different forms of pollutants which come from everything from the exhaust emissions, to the brakes and the tyres and the degradation of the road.

"That’s what we are trying to stop getting into the river in the first place. The tool that we’ve come up with takes this incredibly complex issue of road runoff and with just a few clicks tells the authorities what sort of sustainable drainage system can be used to resolve the pollution.”

Chris Jackson, head of BGS Environmental Modelling, said: “The Road Pollution Solutions Tool, which was only launched just over a year ago, is already showing just how beneficial it is in highlighting which roads in London are at risk of road run-off pollution.

“Expanding this tool further to include an integrated assessment of agricultural pollution risks means that we can assess these pollution sources and explore what can be done to reduce them.”

Pollution causes

Fertilisers, pesticides and animal waste in rural areas can run off into rivers, introducing chemicals and excess nutrients that can cause algal blooms, depleting oxygen and harming aquatic life.

Similarly, run-off from roads can carry oil, heavy metals and other toxic substances into waterways, contaminating the water and affecting ecosystems. These pollutants not only harm wildlife but also threaten the quality of drinking water for communities.

The tool combines pollutant emission factors, local rainfall conditions, surface area and the make-up of traffic on particular routes, using official data to predict where pollution hotspots are likely to occur. Results are shown on an interactive map.

The platform also suggests potential nature-based solutions, such as wetlands, ponds and rain gardens, alongside roads to manage pollution before the water discharges into streams or rivers.

Built on years of research by partners, the first online map was launched in the capital in 2023, partly funded by the Mayor of London, Transport for London and the Environment Agency. It now covers roughly 3862.3 km (2400 miles or 10 per cent) of London’s major roads.

The expansion project, which is funded by the Government Office for Technology Transfer, will last for 18 months.