Durable Growth, Transportation

The realities of reducing neighborhood speeds

Petaluma roundabout

Petaluma roundabout

Even if a neighborhood chooses to accept a lower speed limit, the realities of effecting that change can be daunting.

In earlier posts, I wrote that the joint use of public streets was reduced by the advent of the automobile and that some people are pushing back by proposing a maximum speed of 20 mph in all residential neighborhoods.  (Tying together my recent threads on streets and parks, I’ll note that park use would likely improve under a “Twenty is Plenty” policy.  Parents may be more willing to let children walk to a park if cars were well-behaved.)

Let’s assume for a moment that a neighborhood unites behind the “Twenty is Plenty” concept and wishes to reduce the speed limits on their streets.  How should they proceed to implement the change?  Most would probably assume that a petition to the city council would be the right first step.  They’d be wrong.

Cities have a surprisingly small role in setting speed limits.  Instead, rules written in Sacramento are used to set the speed limits, with only a small bit of local autonomy permitted.  And those rules mandate that the speed limits be established based on how fast we actually drive.

The process is simple and objective.  Vehicular speeds are collected by radar when speed limit signs aren’t present.  The speed limit is then set at the 85 percentile of measured speeds.

Most people are startled when they first learn this.  They’re shocked that speed limits are set by how fast we do drive, not how fast we should be driving.  But it’s indicative of how well the automobile lobby has played the public policy game.

To be fair, cities have a small bit of remaining authority.  A City Engineer can unilaterally reduce the speed limit if he believes that there are traffic hazards not visible to the driver.  But those reductions can be challenged in court by a driver who feels wronged, so City Engineers are cautious in their use.

Some may have spotted a possible loophole in the speed limit process.  They may be thinking, “What if we ask neighbors to drive slowly while the speed data is being collected?  The 85th percentile would be pushed downward and our neighborhood would be safer.”

The idea isn’t new.  I recently learned of a North Bay city that tried the trick.  City employees were recruited to slowly cruise through the speed check area.  At first, the plan worked.  A lower speed limit was established and the police began enforcing it rigorously, with speeding tickets being written.

But as happens with most conspiracies, someone blabbed.  The tale got back to the traffic court judge who was heartily displeased.  The collected traffic fines were returned, the speed limit was raised, and a round of hand slaps was administered.

If we assume that Sacramento isn’t about to change how speed limits are set, what other options do we have?  We can build streets such that the comfort zone of driver is affected, with resulting lower speeds.

In recent years, we’ve already begun seeing some of these driver comfort zone modifications, which are collectively known as traffic calming strategies.

Divided street in Memphis

Divided street in Memphis

Calming strategies are often categorized as horizontal or vertical.  Horizontal modifications can include street markings, such as center stripes or the City Repair intersection painting concepts that were discussed last fall.  Other concepts include narrower streets and center medians.  Even roundabouts can temper traffic speeds, unlike stop signs which sometimes result in dashes between intersections.

Vertical modifications can include speed bumps, speed humps, which are wider than speed bumps and allow higher speeds, and speed tables, which are wider yet and usually include crosswalks or other pedestrian accommodations.  The new East Washington Plaza in Petaluma makes extensive use of speed tables.

But there are two problems with traffic calming strategies.  First, they’re costly.  When cities don’t have the funds to fix potholes, street modifications to reduce speeds are likely out of fiscal reach. Second, public safety agencies, fire, police, and ambulance, often push back.

This isn’t to criticize public safety agencies, but for too long they held too much influence over street geometry.  Streets were built with widths and turning radii such that emergency vehicles could respond as quickly as possible, the street geometry encouraged higher driving speeds thereby pushing up speed limits, and parents began keeping their children inside because of concerns over pedestrian safety.  In one of great ironies of urbanism and vocabulary, public safety became the enemy of public health.

In recent years, public safety agencies have been forced to negotiate emergency access versus pedestrian safety, although not always happily.  Within the past few days, a San Francisco Supervisor and the San Francisco Fire Chief had a public contretemps over street widths in new development.

The balancing act between public safety and public health will hopefully continue.  It’s another reminder of Jeff Speck’s observation that cities should be designed by generalists who can find reasonable balances between alternative goods, rather than by specialists who push only their own agenda.

Even if reducing traffic speeds in residential neighborhoods is a good idea, and I think it is, the path to making those changes won’t be easy.

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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