This week is UN Global Road Safety Week, focused on the theme “Slow Down, Save Lives.” WRI works to make cities around the world safer and more sustainable by implementing street design and regulations that reduce vehicle speeds while supporting walking and cycling. There is a growing body of evidence on the impacts and wider benefits of such efforts, which we’ll explore in blog posts this week.
Deaths and serious injuries are the painful and highly visible result of a lack of road safety, but we have lost more to high car speeds than we realize. What about fear of children playing on sidewalks, walking to school, or learning to ride a bike? What about people who struggle to pay high transport costs, but don’t feel safe commuting by bike?
Speeding cars can limit physical activity, use of public space and quality of life, and the impacts are felt most by the least advantaged . Lower-income residents often live in close proximity to roads with dangerously fast-moving traffic. They are also more dependent on walking, biking or public transport, which are most exposed to the danger of speeding cars. These negative impacts are even more dramatic in developing countries, where a rapid increase in car and motorcycle ownership is taking place on roads with little speed regulation.
Unfortunately, this can literally be a matter of life and death. But establishing safer speeds in cities can not only save lives, it can also generate many other benefits in the process:
1. Lower speeds save lives.
Every 1.6 kilometer-per-hour (1 mph) reduction in vehicle speeds on urban streets results in a 6 percent decrease in traffic fatalities. Lower speed limits reduce traffic fatalities and serious injuries for a combination of reasons. For one, driving at very high speeds can result in tunnel vision and decreased depth perception for the driver. At lower speeds, drivers have a wider field of vision and are more likely to notice other road-users.
At lower speeds, even if a crash does occur, the consequences will be less severe, especially if it involves a pedestrian, cyclist or motorcyclist. A pedestrian has a 90 percent chance of survival if hit by a vehicle moving at 30 kmph (18.64 mph). This decreases to 70 percent at 40 kmph (24.85 mph) and less than 20 percent at 50kmph (31 mph).
Driving at lower speeds also enables drivers to stop within a shorter distance. The stopping distance of a vehicle is a combination of the distance travelled during the driver’s reaction time and the distance it takes for the car to stop after the brakes are applied. At higher speeds, a car travels further during this reaction time and the stopping distance is greater. This affects the rate of momentum at the point of a crash, and therefore the possibility of survival.
2. Safer speed limits don’t necessarily make trips longer.
Many people fear that slowing the speed limit in urban areas will dramatically increase journey time. However, average road speeds in cities are more determined by the frequency of intersections than speed limits.
A safer speed limit can achieve more uniform speeds and reduce dangerous midblock acceleration, while adding little to overall journey times. Research from Grenoble, France has shown that a speed limit of 30 kmph (18.64 mph) rather than 50 kmph (31 mph) only added 18 seconds of travel time between intersections 1 km (.62 miles) apart. Lower speed limits may even reduce congestion in some cases, as they reduce the likelihood of bottlenecks. This has been observed in Sao Paulo, where lowering the speed limit on major arterials reduced congestion by 10 percent during the first month of implementation, while fatalities also dropped significantly.
3. Designing for safer speeds fosters healthier communities.
Lower car speeds create a more comfortable environment for pedestrians and cyclists. Street design that encourages safer speeds—such as narrower lanes and wider sidewalks, raised crosswalks and curb extensions—also provide more space for pedestrians and make it easier to cross the road. Details on these and other measures can be found in WRI’s Cities Safer by Design report.