The wider ambitions of lowering speed limits

Lowering speed limits to appropriate levels goes well beyond reducing collisions, saving lives, and preventing serious injuries for all types of road users; it also has a huge influence on many other objectives for societal well-being.

Environmental benefits

Intense acceleration and deceleration are known to cause greater emissions, increased noise nuisance and increased passenger discomfort, particularly if it is associated with rapid acceleration and deceleration. Slower and calmer driving reduces emission rates for carbon monoxide, volatile organic compounds and oxides of nitrogen, depending on the gear engaged and the level of driver acceleration/ braking. Vehicle speed was found to be a strong contributing factor to the degree of heavy metal contamination, such as cadmium, lead, zinc, and nickel, in road dust.

The largest source of noise in urban areas is traffic-induced noise, which accounts for 80% of all communal noise sources. The Beuhlmann and Egger, 2017 study in the UK, measured traffic noise and found that 30 km/h (19 mph) road speeds reduced acoustic energy levels by about half. Environmental noise has been linked to sleep disorders, heart disease, stress and, among children, decreased school performance, including decreased learning, lower reading comprehension, and concentration deficits.

Health and Quality of Life

Lowering speed limits can also result in broader health impacts. They can reduce the perception of road danger, which may encourage active mobility, namely walking and cycling for transportation which significantly enhances physical activity levels, leading to better physical health. Using active mobility reduces the risk of more than 25 chronic diseases thus increasing longevity .

Social Cohesivity and Community Severance

Lower speeds can improve accessibility and reduce the disconnection caused by roads that become urban barriers. Traffic levels and traffic speeds not only discourage walking and active mobility but limit social contact between residents on opposite sides of the road. In both urban and rural areas, such severance can prevent children from safely crossing from their homes to get to school or prevent safe travel between homes and nearby workplaces.

Travel benefits

In many cases, lowering speed limits have been prevented because of fears that this measure will increase overall travel times and congestion. Research shows that any increases in travel times and congestion are negligible, and in some cases, they can even be improved through reduced speed limits. It is often not understood that in many urban areas, average speeds are already significantly lower than the speed limit due to congestion. The actual speeds in the top 25 most congested cities in the world are well below 30 km/h (19 mph).