Introducing lower speed limits on motorways and urban roads can lead to significant reductions in road accident deaths and also reduce fuel consumption, noise pollution, CO2 and air pollutant emissions. The magnitude of reductions depends on a number of factors including vehicle fleet composition, technologies deployed, driving behavior, frequency and magnitude of speeding, congestion, and traffic diversion due to reduced speed.
- Action applies to both passenger and freight vehicles.
- Application is limited to motorized modes, with main focus on private cars, though this action also has potential application to public transport vehicles (e.g. long-distance buses).
- CO2 benefits are likely to be limited as compared to sustainable development benefits, but tangible reductions in carbon emissions can be gained by operating motor vehicles at lower speeds.
- Speeding regulation is introduced to attempt to improve traffic safety. The World Health Organization identifies speed control as one of various interventions likely to contribute to a reduction in road casualties and recommends that governments set and enforce appropriate speed limits, as well as enhance programs of law enforcement with public information and education campaigns (e.g., on the dangers of speeding and the social and legal consequences of doing so). Speed limits may also be set in an attempt to reduce the environmental impact of road traffic (i.e. vehicle noise, vibration, emissions).
Status of deployment:
- HGVs in the UK have been subject to mandatory 97 km/h speed limiters since the early 1990s, which was subsequently revised to 90 km/h during EU harmonization. Some heavy goods vehicle operators (typically big-name retailers) further reduce their HGV limiters from 90 km/h to a lower speed, typically 85 or 80 km/h, in a claimed bid to reduce fuel consumption and emissions. Globally, all heavy vehicles in developing economies in South America, Latin America and Africa have speed limiters in heavy vehicles.
- It has been estimated that tightening highway speed limits from 120 to 110 km/h could deliver fuel savings of 12–18%, assuming 100% compliance with speed limits. However, relaxing these assumptions to a more realistic figure implies a saving of just 2–3%. For trucks, a speed reduction from 90 km/h to 70-80 km/h could yield 3-8% reductions in CO2 emissions, and meaningful reductions can also be achieved by reducing urban speed limits.