Road Safety Group Argues for "Rational" Speed Limits

The Newspaper
by The Newspaper

In a speech last week before the Institute of Transportation Engineers (ITE), a road safety expert argued that speed limits should be based on engineering, not political considerations. Chad Dornsife, executive director of the Best Highway Safety Practices Institute made his case to an ITE annual meeting in Denver, Colorado. “The solution is to properly engineer our roadways to facilitate the optimum flow of traffic, a prescription that would reduce our total vehicular carbon footprint and improve roadway safety,” Dornsife said. “The future is in educating motorists to drive safely via safety campaigns that promote keep right except to pass, yielding, courtesy, and safety practices that are based in fact. Programs that create jobs, reduce our carbon footprint, pollution, and improve the safety and efficiency of our infrastructure.”

Dornsife opened his presentation by explaining the federal role in setting consistent standards for road signs to prevent 80,000 local and state authorities from creating confusion as motorists travel across the country. The speed limit sign falls under the rules laid out in the federal Manual on Uniform Traffic Control Devices which specifies that the sign should reflect a limit determined by accepted principles of engineering. In a 1985 report, the Federal Highway Administration (FHWA) defined the most effective way to determine the number to print on the sign.

“Based on the best available evidence, the speed limit should be set at the speed driven by 85 to 90 percent of the free-moving vehicles rounded up to the next 5 MPH increment,” FHWA’s report, Speed Limit Synthesis, explained. “This method results in speed limits that are not only acceptable to a majority of the motorist, but also fall within the speed range where accident risk is lowest… No other factors need to be considered since they are reflected in the

drivers speed choice.”

The federal agency’s studies confirm that when speed limits are lowered or raised, the average speed of traffic does not change by a significant amount. Dornsife emphasized the point by citing the experience of Montana between 1995 and 1999.

“What happens when you have no daytime speed limits outside of the city limits, on every classification of roadway, paved or otherwise?” Dornsife asked. “Nothing. Motorists continued to drive at speeds they were comfortable with. Not one fatality was brought to our attention that was attributed to no daytime speed limits.”

The fatal accident rate on Montana highways dropped to an all-time low when the state had no posted daytime speed limit. A speed monitoring site at Great Falls registered a change in average speed of just 1 MPH when the posted daytime limit was eliminated.

Dornsife argued that “politics, power and empires” changed federal policy in the mid-90s to dilute the influence of engineering in the setting of speed limits. New campaigns focused on issuing citations and imposing “zero tolerance” policies. As a result, most speed limits today are set unreasonably low and enforcement resources are misallocated to focus on drivers who are driving at speeds least likely to cause an accident.

Dornsife recommended that the situation could be corrected by undertaking regular surveys of driving speeds so that most roads could be re-posted at the measured 85th percentile speed. The exception would be work zones and school zones that should have 50th percentile speeds.

“Placing an invented number on a sign will not make you safer, but fact based laws that are uniformly applied, and making sure best safety practices are followed will,” Dornsife concluded.

The BHSPI presentation is available in a 1mb PDF file at the source link below.

Speed Limits Presentation to ITE District 6 (Best Highway Safety Practices Institute, 7/15/2009)

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  • Newcarscostalot Newcarscostalot on Jul 21, 2009

    These are the kind of laws that they have in Germany on the Autobahn. People there are taught certain road rules, such as always keep right, unless to pass. If you dont, you get a ticket. Also, there are areas on the Autobahn with no speed limits, because German drivers know how to drive safe, traffic laws are very strict and are heavily enforced. Those are some of the reasons that Germany has lower traffic fatalities even though the Autobahn has no speed limits in places.

  • Anonymous Anonymous on Jul 21, 2009

    @slateslate: Mr. Random Guy who is the self-appointed executive director of his institute Too right. We have here a rather large credibility gap between the messenger and the message. I elected several years ago no longer to devote time to Mr. Dornsife's phone calls and e-mails; my discretionary time for pointless folly is limited and I find it more productively spent watching "The Simpsons" or something. A couple years ago, a NHTSA lighting compliance enforcement engineer gave a presentation at the SEMA show, the intent of which was to give a general overview of what kinds of lighting equipment are illegal and why; there's always an enormous amount of unsafe, noncompliant lighting gear at SEMA, and this engineer—who happens to be quite knowledgeable and personable—was trying to bring vendors onside rather than just nuke 'em with the full weight of his agency. The presentation was no high-handed "because we say so" kickaround, it was clear and detailed and educational. Nevertheless, Dornsife threw a grand mal temper tantrum — no exaggeration; he was hollering and screaming, red in the face, up out of his chair and pounding his fist on the conference table we were all sitting around, belligerently interrupting, baselessly but repeatedly insisting he's right and everyone else in the room is wrong, mocking the NHTSA guy in elementary school playground fashion, responding to reasonable offers like "If you will show us data to support your assertion that the rule is wrong, we'll probably change it" with "I don't have to show you any data! I'm right! Use your freakin' eyes!". It was a hell of a display of utterly misdirected hystrionics; the NHTSA guy was in the enforcement division, not the rulemaking. Even if he'd completely agreed with Dornsife, he was utterly powerless to change the rule. Dornsife was doing exactly the equivalent of abusively ranting about a speed limit to a cop trying to decide whether or not to write a ticket. At the time he was a vendor of unsafe lighting equipment (gee…) living near Las Vegas. Now it looks as though he's moved to Portland and rebranded himself. He's right, of course, that V85 is the right way to set speed limits if the goal is to maximise compliance and flow and minimise crashes. There's decades' worth of data, a mountain of it from all over the world, robustly demonstrating that to be the case. It's likewise completely plain that speed limits set arbitrarily or artificially low are the right way to maximise revenue and/or advance political careers (think of the children!). But as has been amply pointed out in this discussion, Dornsife didn't tell the ITE assembly anything they don't already know well enough to recite it backwards in their sleep. He didn't "argue" anything. He didn't persuade anyone. I'd bet money everyone in the room tuned him out and caught up on email while he talked. All he did, as it seems, was some self-promotion. Judging by the presence of this "news" article here on TTAC, it worked.

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