Adding Neighborhood 20 MPH Zones Isn’t a Zero-Sum Game

An exhaustive report published in the British Medical Journal found that traffic injuries declined in London's 20 mph zones and, to a lesser but still significant extent, on the streets immediately adjacent to the zones. Image: ## Medical Journal##

The Brooklyn Paper ran one of its trademark neighbor-vs.-neighbor stories today, turning a weekend public workshop about implementing a 20 mph zone in Park Slope into an occasion for more conflict-driven reporting:

Greenwood Heights activists claim drivers heading south on Sixth Avenue already speed up once they cross the Prospect Expressway and hit a five-block stretch between 20th and 25th streets with no stop signs.

“It’s already treacherous,” said resident Sarah Raskin. “This would divert unsafe driving from one neighborhood to another.”

Sounds like streets in Greenwood Heights need traffic calming too. And in fact, the Greenwood Heights residents quoted in the Brooklyn Paper seem to be saying they’d welcome a slow zone that encompasses their neighborhood.

It would be great to see a blanket 20 mph speed limit — pioneered by NYC DOT in the Bronx neighborhood of Claremont — extend to many neighborhoods at once. But if Park Slope gets a slow zone before Greenwood Heights, or if Greenwood Heights gets a slow zone before Park Slope, research suggests both neighborhoods will still be better off.

The definitive piece of research on 20 mph zones was published in the British Medical Journal in 2009. Reviewing 20 years of data, researchers found that London’s 20 mph zones, a patchwork of neighborhoods that expanded gradually over many years, prevent 27 traffic deaths and serious injuries annually. Within the zones, serious traffic injuries and deaths fell 46 percent, and children sustained 50 percent fewer casualties.

Significantly, the authors reported that the data “suggests that casualties inside 20 mph zones are not being displaced to nearby roads.” And on top of that, they found a spillover effect, with traffic injuries and deaths declining eight percent in areas adjacent to the slow zones (within 150 meters, or about two NYC blocks).

Adding slow zones is not a zero-sum game.

  • Brooklyner

    Natalie O’Neill is simply a terrible journalist. Her main goal is to find controversy in the least controversial subjects.  Slow car speeds that save lives should not be controversial to anyone except NASCAR drivers.

  • Lisa Sladkus

    This is why we want 20 mph speed limits for the entire upper west side. Let’s not pit communities against one another. We ALL deserve safer streets and a huge factor is slowing traffic down. 

  • Mark Walker

    Thank you Lisa Sladkus. I second the motion.

  • Eric McClure

    All in favor? Aye.

  • Anonymous

    I said it before I’ll say it again:

    What difference does a 20MPH speed limit make if it is not enforced?

  • J

    @YouandWhoseArmy3D:disqus  The implementation of 20mph zones includes gateway treatments and pavement markings telling people that they are entering and driving in a slow zone, as well as street width reductions and speed humps to force drivers to slow down. DOT intends the program to be self-enforcing, but we won’t be able to see how effective it really is until it’s been in place for a bit.
    Here is a description of the program: is a presentation about the first slow zone in the Bronx:

  • ed

    How amazing! I mean, that’s something!
    But I don’t quite understand it.
    convert mkv to avi

  • ed

    How amazing! I mean, that’s something!
    But I don’t quite understand it.
    convert mkv to avi

  • This is really good insight. Thanks I liked it very much.

  • Thank you Lisa Sladkus. I second the motion. We ALL deserve safer streets and a huge factor is slowing traffic down.
    convert flv file to mp4


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." […]

Wiki Wednesday: Twenty’s Plenty

Excellent StreetsWiki use by Streetsblog regular ddartley, who added the pic you see below to the entry on 20 mph zones. From author Andy Hamilton: In July 2008, the British Medical Association called for the application of 20 mph zones throughout residential neighborhoods, not just in the vicinity of schools, where they are commonly applied. […]

No Need for Speed: Twenty MPH Is Plenty for Us

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