Against a backdrop of motor-normativity domestic transport and its associated emissions continue to rise. From 16% in 1990 to 29% in 2023, domestic transport has been the single biggest source of the UK's territorial emissions since 2014.
Reliance on private cars generates high levels of congestion, contributes significantly to regional greenhouse gas emissions, and worsens air quality. In the UK, 68% of roadside NO₂ concentrations in 2023 originated from NOx emissions from exhaust pipes. Parts of Rotherham recorded peak annual average NO₂ concentrations of over 60 µg/m³ in 2023, which is more than six times the World Health Organization (WHO) guideline of 10 µg/m³.
SYSC’s project looking at developing transport routes explored how transport infrastructure could be developed to improve accessibility to places and opportunities, whilst reducing carbon emissions and improving health and wellbeing. As part of SYSC’s Consolidated Research Report, the “Improving Air Quality” case study explored this challenge.
Key Insights
Whilst some journeys can and should be shifted to alternative modes of transport, motorised vehicles will remain a significant part of the transport system - only with fewer cars on the road, that are driving fewer miles, can we deliver significant improvements in carbon emissions, air quality, journey times and journey experiences. Therefore, policy and technical innovation is needed to temper the social and environmental costs associated with private and commercial vehicles.
The “Improving Air Quality” case study found that re-routing vehicle traffic using a pollution-optimal traffic assignment model (TA) can reduce congestion and achieve a 21% reduction in Sheffield-wide NO2 concentrations, reducing the number of roads exceeding the WHO recommended limits from 37% to 30%. Traffic re-assignment could also reduce the number of roads exceeding 20μg/m3 - a level associated with elevated long-term health risks - from 8% to 5%. Moreover, these gains are not accompanied by significant time penalties for drivers - the average increase in journey times is just ~20 seconds showing that health and environmental benefits don’t need to come at the cost of major inconvenience.
