20 is Plenty (except when it isn’t): NMA E-Newsletter #609

The warning signs have been around for a long time. The scramble to fall in line with Vision Zero demands that traffic fatalities be eliminated regardless of the cost to taxpayers, and society in general, has even affected organizations like the Institute of Transportation Engineers that are supposed to be protecting the engineering standards that keep our roads safe and efficient.

ITE currently is considering a new policy statement under the heading, “Vision Zero and Safe Speeds.” The recommendation to its membership of traffic engineers and other transportation professionals is to fully embrace and support Vision Zero.

One of the catchphrases used in the ITE community is “20 is plenty.” The reference is to a forced reduction of posted speed limits to 20 mph in our cities. Boston is one city that dropped its statutory limits from 30 to 25 mph, and based on false reporting that the change caused drivers to slow down, it is considering another reduction to 20 mph.

Recently, a discussion thread was started on the ITE member forum asking fellow members about the success of 20 is Plenty programs. Jay Beeber, Executive Director of Safer Streets L.A. and NMA Life Member, had seen enough when he posted the following takedown of the whole approach:

“Can we please stop pushing the “20 is plenty” nonsense and other arbitrary setting of speed limits? This is not a scientifically-based approach to speed management. The foundation of engineering is science and data, not ideology. The overwhelming scientific evidence is that arbitrarily lowering (or raising) speed limits on local roads has little to no effect on actual speeds, and therefore little to no effect on safety. There are scores of studies over the years that prove this. All it does is make violators out of the vast majority of drivers.

“I realize that for some, criminalizing driving is a feature of these policies, not a bug. But this approach can lead to very negative societal consequences. For example, anyone who is concerned about the over-policing of minority communities for minor infractions should recognize that criminalizing a majority of the driving population will make this problem much, much worse. I wonder how you might feel if you pushed this policy, and someone gets pulled over for going 30 mph in a 20 mph zone that was previously 25 mph, the stop goes south, and someone ends up dead.

“It has been said before, and it bears repeating over and over since it has still not gotten through to some folks, but the only way to reduce speeds (assuming that’s a necessary policy on a particular roadway) is to change the nature of the roadway in some manner that changes the driver’s perception of their speed. Otherwise, you are on a fool’s errand and will simply create pain and misery for the populace, give people a false sense of security, waste resources that could otherwise be put to effective safety measures, and create disrespect for traffic control devices, elected officials, and law enforcement.

“Massive enforcement efforts will not achieve the desired goal. Drivers are capable of complying with an uncomfortably low-speed requirement for about a block or two (such as a school zone). After that, the natural tendency to match your speed with your perception of the “comfortable” speed for that situation and roadway will take over. Humans cannot control these perceptions as they are primarily a function of the autonomic nervous system, and no amount of draconian penalties can change the natural perception-reaction response.”

The reaction to Jay’s post was mixed, with some rooting him on and others rooted in Vision Zero principles. The most notable response came from Martin Parker, P.E.. Mr. Parker researched and wrote the seminal study on the topic, “Effects of Raising and Lowering Speed Limits on Selected Roadway Sections,” which was published in June 1996 by the Federal Highway Administration. He posted:

“Thanks, Jay, for your comments and insight into the issue of 20 is Plenty. Yes, I was one of those who conducted a nationwide study in the 1980s and early 1990s to examine the effects of raising or lowering posted speed limits. The typical result was a change in speed of less than 1 mph. Sometimes lowering the speed limit increased average and 85th percentile speeds, and sometimes raising the speed limit lowered average and 85th percentile speeds. You never could predict the result in changing a speed limit sign, but the result was always close to no major change in speeds.

“Yes, you can provide massive amounts of enforcement to enforce an artificial posted speed limit, but as soon as the special enforcement is reduced, you are left with the same speed curve. Today our proud enforcement officers have issues greater than devoting resources to an artificial limit.

“If we are really interested in Vision Zero, then we need to make these areas “safe” for pedestrians and other non-motorists. The only way I know of doing this is by declaring the section an Auto-Free Zone. No automobile or trucks allowed in the zone. Then you might have to regulate bicycles operating in the zone, but vehicle speeds would not pose a problem.”

The experts have spoken. Our job is to make sure the engineers and policymakers are listening and taking this seriously.

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