Durable Growth

Can twenty be plenty?

Typical California arterial street

Typical California arterial street

In my last post, I wrote about how our grandparents and great-grandparents yielded our streets to the automobile in the early 20th century, with the result that we’re no longer even allowed to hold block parties in the street.

Before the advent of the automobile, most street uses occurred at speeds and intervals that didn’t threaten nearby people.  Faced with the motor vehicle, capable of outrunning a drayage wagon or horse-drawn cab, able to sustain those speeds for hours, and often driven by a partially-skilled operator, our ancestors had two choices.

They could have restricted automobiles so streets remained comfortable for all users.  Or they could have abandoned the streets to cars, pushing the other users to the fringe of the right-of-way or even to oblivion.  Under a strong lobbying effort from the automobile folks, they chose the latter.

That decision had dramatic consequences, ones that have been true for all of our lives but are still startling when we consider them anew.

My front door is about forty feet from a traffic lane.  The speed limit on my street is 25 mph.  But, despite the stop signs at both ends of the block, drivers often reach 30 mph by the time they reach my home.  And pedestrians usually die if struck by a car traveling 30 or more mph.

So, forty feet from my door, a distance I can cover in fifteen strides, is a place where, unless the driver spots me in time, I can quickly become a traffic fatality.  When I chat across the street with a neighbor walking her dog on the far sidewalk, a killing zone lies between us.  I find that creepy.

But there may be an alternative.  In Happy City, Charles Montgomery writes that the probability of a car/pedestrian collision being fatal to the pedestrian drops quickly below 30 mph.  By 20 mph, the pedestrian is very likely to survive.  Montgomery even speculates that pedestrians have an innate understanding of this fact, so become more comfortable when nearby vehicles travel at closer to 20 mph.

In Walkable City, Jeff Speck writes that many European communities are recognizing this possibility and pushing for a maximum speed of 20 mph in all residential zones.  Their slogan is “Twenty is Plenty”.  And they’re making progress.  The “Twenty is Plenty” group in Great Britain claims that over 13 million Brits now live in communities that have adopted the “Twenty is Plenty” standard.

Typical California residential street

Typical California residential street

The concept has been slower to take root on this side of the Atlantic, with the greater expanses of U.S. suburbia acting as an implicit counterargument.  But there have been pockets of progress.  In an article from 2010, Grist writes about residents in Hoboken, New Jersey arguing for a 20 mph standard.  In the quixotic hope that sarcasm can help sell the idea, Grist describes the crusade as a “crazy stance against running over children”.

More recently, residents of Brooklyn have been surreptitiously posting guerrilla traffic signs with “20 is Plenty” as a run-up to a lobbying effort at the state capitol, where they’ll argue for greater local control over speed limits.

For those of us, which is pretty much everyone, who grew up with residential speeds of 25 mph or higher, it may seem awkward to poke along at 20 mph.  But I’ve been occasionally driving the lower speed on streets near my home.  (Warning: Don’t do this if there are cars behind you.  The drivers can quickly become agitated.)

The lower speed can soon become comfortable, with a feeling of rightness to it.  There’s more of a sense of being part of the neighborhood, rather than hurrying through to another place.

And if one has a trip of a mile through residential streets before reaching a collector or arterial, which is fairly typical, the travel time difference is only a minute, which seems a small price to pay for restoring a balance between cars and other users of the street.

If we check the possible 20 mph standard against Speck’s four criteria for walkability, we find that it improves both pedestrian safety and comfort, putting us halfway to a more walkable city.

However, converting a neighborhood to a 20 mph zone is a complicated, nearly impossible, task under California laws and mindset.  When I next return to this topic, in about a week, I’ll write about these issues.

Before closing, I’ll touch on cul-de-sacs.  Some readers may be congratulating themselves for living on cul-de-sacs, thinking that cul-de-sacs aren’t subject to the 30 mph speeds noted above.  Those readers are partially correct, but don’t get partial credit.

While cul-de-sacs, particularly short ones, don’t have speed problems, what they’ve done is shunt travel to other streets where the speed issues are at least as bad, if not worse, as drivers speed to make up for the out-of-direction travel required by cul-de-sacs.  At best, residential traffic under the current mindset and rules is a zero-sum game, with cul-de-sacs exporting their portion of the problem elsewhere.

As always, your questions or comments will be appreciated.  Please comment below or email me.  And thanks for reading. – Dave Alden (davealden53@comcast.net)

Written by Dave Alden

Dave Alden

Dave Alden is a Registered Civil Engineer. A University of California graduate, he has worked on energy and land-use projects in California, Oregon, and Washington. He was also the president of a minor league baseball team for two seasons. He lives on the west side of Petaluma with his wife and two dogs. The blog that he writes can be found at http://northbaydesignkit.blogspot.com.

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