Cars in Paris will soon be going très slow. The city’s new mayor, Anne Hidalgo, recently introduced a plan to lower the default speed limit throughout the city from 50 kph (31 mph) to 30 kph (a little slower than 19 mph). Though billed as an anti-pollution plan, it will make streets safer for pedestrians, Le Parisien reports.
Since the first “Tempo-30” zone was introduced in Buxtehude, Germany, in 1983, the traffic-calming measure has been adopted by other European cities, including Stockholm, Munich, Dublin, and Barcelona. The policy has largely been implemented by smaller cities and only in residential areas, though, making the Parisian plan, which will affect the city’s 2.2 million* residents, notable for its scale. Studies have shown that reducing speeds to 30 kph or less both reduces the total number of accidents and how fatal accidents are for pedestrians. London‘s 20 mph zones, mostly in residential areas, have reduced the frequency of fatal and serious injury accidents by 53%. The creation of 78 slow zones in the city lowered the annual injury accident rate from 1,660 total accidents to 590, and 282 fatal accidents to 77. And according to experts, the slower speed limit doesn’t necessarily cause more traffic jams.
In Paris, the 30 kph limit will apply to most streets, excluding some major thoroughfares like the Champs-Elysées. The initiative, which does not have a roll-out date yet, represents larger efforts by Parisian administrators to slow traffic to protect pedestrians and reduce CO2 emissions (though the effects of slowing down to 30 kph on emissions aren’t entirely clear). Earlier this year, the city reduced the speed limit on its busy ring road, Boulevard Périphérique, by 10 kph, down to 70 kph or 43 mph. (Critics noted that the change made no difference, since congestion kept traffic at a crawl anyway. Under the new plan, its speed limit will remain 70 kph.) A little more than a third of the city’s streets already had 30 kph speed limits, as per a September 2013 initiative, and certain sections of the city where cyclists, pedestrians, and cars are likely to mingle, called “meeting zones,” are limited even further, to speeds of 20 kph or less.
You might assume that lower speed limits slow drivers’ travel time, but that’s not usually the case. On urban streets, “a lower speed limit may actually reduce overall travel time by allowing a more harmonic traffic rhythm,” according to a study from the Accident Research Center at Monash University in Melbourne, Australia.
Congestion in cities is “all about competing demand at intersections,” as Tom Vanderbilt, author of the book Traffic: Why We Drive the Way We Do, explained to me in an email. “Drivers speeding toward a red light, stopping, and restarting can actually cause more congestion than if everyone just drove more slowly and timed their approach to their light.”
And ensuring that urban drivers keep speeds down under light traffic conditions could save a significant number of lives. Research has shown that the risk of pedestrian fatality rises sharply at speeds higher than 30 kph. A U.S. National Highway Traffic Safety Administration report found that only 5% of pedestrians hit by a car going 20 mph or less died, compared to 40% struck by a vehicle going 30 mph and almost 100% of pedestrians struck by vehicles going 50 mph or faster.
Paris is not the first city to test out 30 kph zones as a pedestrian-protecting measure, though it may be one of the largest cities so far to make 30 kph the default speed limit. In 1992, Graz, Austria (population: 265,778), made 30 kph the default speed limit citywide.
These 30 kph zones are also a vital component of Sweden’s Vision Zero policy, which aims to reduce pedestrian traffic fatalities to zero. There, as well as in cities in the Netherlands, Ireland, and the U.K., speeds have been reduced to 30 kph in most residential zones and some city centers. The Greens/European Free Alliance, a political group within European Parliament, wants to make it an even broader policy: it recently proposed making 30 kph the default speed limit throughout the European Union.
The U.S. is still playing catch up. New York City has been experimenting with 20 mph zones since 2010, but recent plans to reduce the default speed limit to 25 mph (as part of New York’s Vision Zero) have been stalled by state lawmakers.
*The original version of this post listed the population of Paris as 2.2 billion, rather than 2.2 million. Thanks to commenter Kenny Landes for pointing out the error.