How London Is Saving Lives With 20 MPH Zones

One of London's 20 mph zones, with physical traffic calming measures and the speed limit prominently displayed. Image: ITDP-Europe via Flickr.

When Mayor Bloomberg announced that the new pedestrian spaces in Midtown are here to stay, he made special note of the safety improvements on Broadway, which he called "reason enough to make this permanent." And after the mayor told reporters that the city was getting lots of requests for similar livable streets treatments, the speculation started: What's next?

To replicate the Midtown street safety benefits throughout the five boroughs, New York could look to the example of the UK, where 20 mph zones have reduced automobile speeds across the country. The global city that perhaps most closely resembles NYC -- London -- has been installing 20 mph zones for the last decade, and they are saving lives. Already, 27 fewer Londoners are killed or seriously injured each year because of them.  

The standard speed limit in London, as in New York, is 30 mph. Since 2001, however, London has built more than four hundred 20 mph zones, as described in a 2009 report by the London Assembly [PDF]. The zones are located in residential neighborhoods or near areas of high pedestrian activity, like schools. As of last year, they covered 11 percent of the total road length of the city.

The safety effects of the 20 mph zones have been enormous for pedestrians, cyclists, and drivers alike. In London, serious traffic injuries and fatalities have fallen by 46 percent within the zones, according to the prestigious British Medical Journal. Deaths and serious injuries sustained by children have dropped 50 percent. There's even a small spillover effect, with areas immediately adjacent to 20 mph zones seeing an eight percent reduction in total injuries and deaths. The science is so clear that in 2004 the World Health Organization endorsed 20 mph speeds as an essential strategy to save lives. 

These 20 mph zones do much more than change a digit on speed limit signs. London's zones include a host of traffic calming measures to make the speed limit self-enforcing: road humps, raised junctions, chicanes, and raised crosswalks are the most common. Increasingly, speed cameras are used to enforce lower speeds.

When paired with hard hitting public service announcements like these, London is addressing each of the three E's of traffic safety: engineering, enforcement, and education. As a result, the 20 mph zones really work, silencing skeptics who claimed that Londoners would just keep driving as they always had. As implemented, overall speeds in London's 20 mph zones have decreased by nine miles per hour, according to the London Assembly report. Transport for London recently recommended
880 more sites for the traffic-slowing treatment.

A 2008 map of London's 20mph zones. Image: London Assembly.

Across the UK, the last few years have seen a shift away from engineering-intensive 20 mph zones and toward blanket 20 mph speed limits. Nationally, two million people now live on streets with 20 mph speed limits.

The impetus for this strategy came from Europe, said Rod King, the director of the national 20's Plenty For Us campaign. While visiting a German town famous for its large population of cyclists, King was surprised to see that the town's bike infrastructure wasn't particularly developed. Instead, he said, "In the early 90s, they reduced the speed limit on all residential roads to 30 kilometers per hour," or 18.6 mph.

Inspired, King helped bring the idea back to the UK. After starting within the bike advocate community, the push to slow down cars quickly expanded. Advocates for pedestrian safety, public health, and even some safety-minded driving groups quickly banded together behind the idea. "It's been accelerating dramatically in the last two years," said John Whitelegg, a professor of sustainable transport and a local councillor in Lancaster.

One benefit of changing an entire city or neighborhood to 20 mph speed limits is the cost, which King says may average 50 times less than London-style 20 mph zones. Another plus is that a uniform speed limit reduces confusion over constantly changing rules.

Campaigning for slower streets in the town of Harestock, UK. Photo: Martin Tod/Flickr

Perhaps the most convincing argument for a blanket 20 mph speed limit is that it helps residents buy into the concept of driving more slowly. According to King, the fiercest opposition comes from those who have to drive through 20 mph speed limits but still live on fast-moving streets. "They don't own the benefits of the 20 mph zone where they live," he said, "but they still have to pay the cost." When a large contiguous area is covered by lower speed limits, it's easier for everyone to make the psychological switch to slower speeds.

Today, 20 mph streets enjoy widespread popular support.
The London Assembly noted that three-quarters of UK residents favor the use of 20 mph zones, though the country strongly prefers enforcement cameras to physical calming
measures.

Despite their current popularity, it wasn't easy to make 20 mph roads a reality. After a 1996 report by the national Department for Transport showed how much safer slower streets would be, it took another three years for the national government to allow local governments to reduce speed limits without explicit approval. Political opposition was often intense. Many conservatives "take the point of view that the correct approach to road safety is just for parents to teach their children correctly," said Whitelegg.

Over the last few years, however, 20 mph speed limits have been sweeping across the UK. Portsmouth recently became the first British city where every residential street has a 20 mph speed limit, and nine others have already committed themselves to doing the same, according to Whitelegg. Eight of London's 32 boroughs are moving towards a blanket 20 mph speed limit. The national Department of Transport is recommending 20 mph limits for all urban residential streets. 

Over a relatively short time, a broad swath of British cities and towns accustomed to 30 mph speeds have embraced the safety and quality of life that slow streets have brought. If any big city in America is ready to follow suit, it should be New York, where more people live without cars than in London.