Engineering Group Takes on High Speed Limits

Photo:  Insurance Institute for Highway Safety
Photo: Insurance Institute for Highway Safety

Speed limits on urban streets will no longer be set almost exclusively by how fast drivers choose to drive.

The National Committee on Uniform Traffic Control Devices, a powerful group of engineers, voted last week to require city transportation officials to consider “pedestrian and bicycle activity” when determining the speed limit on most urban and suburban streets. The changes will be incorporated into the Manual on Uniform Traffic Control Devices — perhaps the most important traffic engineering manual — when it is revised some time in the next few years.

Here’s why this is so profound: Current guidance on speed limits conform to the infamous “85th percentile rule,” which pegs the speed limit on any particular roadway to the speeds of the fastest 15 percent of drivers in “free-flowing conditions.” So if 85 percent of the drivers stay below 40 miles per hour and 15 percent of drivers exceed it, that becomes the speed limit, even if 40 miles per hour is a bit too fast for that roadway.

Critics say that such a rule raises the speed limit to what drivers want as opposed to what is safe for that road’s condition or context. The current edition of the Manual on Uniform Traffic Control Devices say that engineers may use other criteria — like the presence of pedestrians — in setting speed limits. But the new language orders them to use that information in addition to the 85th percentile rule.

“It has the potential to have a significant impact,” Peter Koonce, an engineer with the City of Portland and a sitting member of the NCUTCD, told Streetsblog.

The engineering group also voted to strike language that said the speed study should be conducted in “free-flowing” traffic conditions.

“That’s really a recipe for getting higher speeds,” said Koonce.

The League of American Bicyclists called the changes “welcome improvements,” but the organization added that NCUTCD should have gone further.

The rule changes come as there has been growing awareness of the dangers of speeding, especially as traffic fatality rates have been surging. In 2017, the National Transportation Safety Board sounded the alarm about the issue and suggested rethinking the 85th percentile rule.

Speed management is important for everyone’s safety, including drivers. But it can be especially critical for pedestrians. A pedestrian struck by a car at 40 miles per hour has a 55 percent chance of surviving compared to a 88 percent chance at 25 mph.

NCUTCD refused to provide Streetsblog the approved language for several weeks so this reporting relied on third-party documents.

  • JoeyBaggs

    what about my freedom not to be crippled by some jingo asshat doing a 40 downtown? where is my freedom?

  • JoeyBaggs

    absolutely, please hit them with tickets, i wish my city did ANY speed enforcement

  • thielges

    The 85% guideline also enables setting dangerous speed limits, Consider two roads with exactly the same geometry: width, straightness, lanes, lane widths, stoplights, etc. One is out in the middle of nowhere. The other runs through the middle of a city with more activity. Driver behavior is influenced mostly by road geometry. A speed appropriate for the middle-of-nowhere road is not safe for the city, yet the 85% guideline would allow that unsafe speeds. That’s why local control is important and the 85% guideline should not be considered a rule.

    And indeed in practice we make exceptions near schools and when rural roads pass through small towns. The road geometry does not change in those cases. Without lowered speed limits drivers would blast through at full speed.

    It is so easy to avoid speeding tickets that I can’t even understand why this is an issue. If you pay attention to the road you can avoid a ticket. If you’re negligent then you might get the ticket you deserve.

  • DukeGanote

    If the two roads are identical (same distance between stoplights, same access points, same traffic, same geometry) there’s no reason that anyone can see for a different speed limit. When drivers “drive the road”, rather than political fantasy, the roads would have similar speeds and speed limit (you’ve described an urban throughway, I think.)

    School zones generally include specific times of application, not 24×7.

    Small towns often, at least where I live, specifically incorporate rural roads in order to harvest revenue. They feign surprise that just moving village limit signs and posting lower limits doesn’t change the road, conditions, geometry, traffic volumes, or driver behavior. For just one example: “ODOT did a speed study 1995 which classified the road as 50 mph, but village officials wanted the limit to be slower. They took it upon themselves to place the inaccurate [35-mph] sign in attempt to slow traffic heading into town from the East.”
    https://nbc24.com/news/local/suspicious-speed-limit-signs-cause-controversy

  • thielges

    Duke – Where in that article does it imply that Whitehouse, OH placed those speed limit signs to harvest revenue? It seems more likely they lowered the speed limit to improve safety. Take a look at that lead image and you’ll see that 35 MPH speed limit is right before a library, a bike and pedestrian trail crossing, and a fire station. A couple of blocks further west that road crosses Whitehouse’s main commercial drag. It is understandable that Whitehouse felt that allowing traffic to blast by at 60 MPH was incompatible with the current land use.

    This is a great example for why the 85% guideline is flawed. Blind bureaucracy vs. reality.

  • Andrew

    Now consider what would have happened if you had been behind the wheel of a car.

    Only motor vehicles have the mass and speed necessary to cause the immense degrees of carnage that they, in fact, cause. Anybody choosing to operate a motor vehicle needs to understand and respect the capability of that motor vehicle to cause harm and needs to accept the grave responsibility to operate the vehicle with the utmost of care and full compliance with all laws and regulations.

    Good thing you were on a bike.

  • Andrew

    There’s no 85th percentile rule.

    There’s a guideline based on a 1964 paper that looked at crash rates on rural highways. It concluded that crash incident rates are lowest when speed variability among vehicles is low. If there’s no feasible way to enforce speed limits – I don’t believe any automated enforcement systems existed in 1964 – it might be a good idea to post speed limits roughly in line with common usage.

    But the paper also concluded that crash severity is significantly greater at higher speeds, which the 85thers often forget. And the paper explicitly did not consider impacts on pedestrians or cyclists, and it confined itself to rural highways, which the 85thers often forget when they try to apply their “principles” to cities and other areas with pedestrian/cyclist safety concerns. The 85thers also often forget that modern speed enforcement systems, which didn’t exist in 1964, can yield low speed variability even at speeds lower than drivers might personally prefer to drive – thereby claiming both the low crash incident rates that come with low speed variability and also the low crash severities that come with lower speeds, while also being relevant in urban areas that have pedestrians and cyclists.

    It’s 2019 now. Time to move past a deliberate misread of a 1964 paper.

  • Andrew

    Did you realize that you can opt out of contributing to that profit, in one simple step?

  • DukeGanote

    No, you’ve mistaken the so-called “Solomon curve” (see wikipedia) with the “85th percentile” guidance for speed limits. One anti-85th%tile assessment notes: “there are references to the 85th percentile rule as far back as 1956 in an excerpt from Nation’s Business, a magazine from the U.S. Department of Commerce, in which the author J. Edward Johnston states: “Many traffic authorities agree that a limit which includes 85 per cent of the drivers is reasonable (Johnston, 1956)”. Certainly the 85%tile predates David Solomon’s publication if by 1956 “many traffic authorities” are advocating it. https://drive.google.com/file/d/1pQQTtQpjn2x-Dzi78tA4ddSiq9Mhk7dz/view

    The 85th%tile reflects actual driver behavior. If that’s unacceptable, then re-engineer the roads for the convenience of bicyclists. That works; however, there may be unintended consequences: https://thesunbest.com/vision-zero-a-road-diet-fad-is-proving-to-be-deadly/

  • Andrew

    You cited the study, and now you’re proclaiming it too small to be reliable. So why did you cite it?

  • DukeGanote

    The library, trail crossing, etc. you’re looking at probably didn’t even exist in 1995 on the eastern end of “State Route 64 between Cemetery Road and Gilead Street.” Google-street-view shows how the library-trail-area area looked in 2013 by Indianapolis Road (near Gilead Rd): https://tinyurl.com/WhitehouseOH64 That eastern section may warrant a lower limit as it is near the village core now.
    However, the western area of Route 64 nearer Cemetery Road is entirely different: https://tinyurl.com/WhitehouseOH64E1 Typical rural NE Ohio flatland with long sight-lines. Of course Village officials don’t mention where the tickets are issued; it wouldn’t surprise me if they’re on the western side, not more developed eastern side.

  • Andrew

    Cities do NOT do this.

    You don’t know (or care) what cities do.

    It is a racket.

    Whatever you want to call it, there’s a really easy way to opt out of paying into it. Shall I elaborate or can you figure it out yourself?

  • Andrew

    I’m not sure how anyone takes your fringe group seriously.

    Don’t worry, nobody does.

  • Andrew

    very few people care what the signs say

    …unless there’s adequate enforcement.

    You know, kind of like every other law: if it isn’t adequately enforced, it’s as if the law doesn’t exist, and people act as they please.

  • Andrew

    (As you yourself say in your 1993 study – which, by the way, was close to 26 years ago – “no permanent enforcement presence.”)

  • Andrew

    If the two roads are identical (same distance between stoplights, same access points, same traffic, same geometry) there’s no reason that anyone can see for a different speed limit.

    Yet the one in the urban area that carries pedestrians requires lower speeds, so that motorists have adequate time and attention to watch for pedestrians. That’s why the speed limit needs to be lower in the urban setting, and it needs to be enforced if motorists don’t voluntarily comply with the lower speed limit. It isn’t sufficient to let motorists decide for themselves what seems OK, since what seems OK to them may be too fast for them to watch for (e.g.) pedestrians crossing at crosswalks.

  • jcwconsult

    The 85th guideline is not flawed because raising or lowering posted limits by up to 15 mph will change the actual 85th percentile speed by a maximum of 3 mph, but usually by 0 to 2 mph. This is 1992 research by Parker on BOTH urban and rural roads. The 85th principles are the same on freeways, highways, county roads and main collectors or arterials in urban areas. Only changing the engineering of the roadway will change the actual travel speeds.
    James C. Walker, National Motorists Association

  • Andrew

    I trust you realize that you’re arguing with someone who believes that a speed limit is somehow unjust if it requires drivers to drive more slowly than they’d prefer.

    (Is a tax code unjust if it requires taxpayers to pay more in taxes than they’d prefer?)

  • Andrew

    It is so easy to avoid speeding tickets that I can’t even understand why this is an issue.

    It’s an issue because of the entitlement that many drivers feel to drive as fast as they want, whenever they want, wherever they want.

  • jcwconsult

    I study research, investigative reporters data, and speed studies from across the country. This country has a multi-billion dollar speeding ticket industry, strongly supported by the for-profit insurance industry which often makes two to four times as much revenue from a ticket than the courts. It is one of the most vicious fraudulent rackets ever perpetrated on the public.
    James C. Walker, National Motorists Association

  • jcwconsult

    Actually, more and more people are aware that traffic enforcement is often a for-profit racket. It is why speed and red light camera programs are reducing. It is why investigative reporters and some official government reports are revealing that red light cameras commonly increase accident rates. “Safety programs” that cause accidents are NOT safety programs – they are for-profit rackets.
    James C. Walker, National Motorists Association

  • DukeGanote

    O? “The speed limit had been set at 50 mph, but has now be cut in half to 25 mph… the multi-week study was completed on Wednesday and found that over 85 percent of the vehicles traveling on the two roads was going 30 mph or less.” http://www.ifiberone.com/wenatchee/speed-limits-on-two-local-roads-near-squilchuck-chopped-in/article_0ed9d804-f98e-11e8-9c6e-b36598d137c8.html

  • jcwconsult

    The small Montana study supports the general principle of posting limits near the 85th speed is correct procedure – but is too small to be definitive for their specific conclusions that the 85th speed minus 5 mph produces the best results.

    The Auburn University study supports the general principle that small violations into the red do not cause accidents, but the study is too small to be definitive for their specific conclusion that violations up to 3.5 seconds into the red do not cause accidents.

    James C. Walker, National Motorists Association

  • DukeGanote

    Now you’ve set up a difference in the roads by including pedestrian traffic (without any indication of sidewalks, etc.), which wouldn’t be true on an urban thruway, as I’d stated in my reply.

  • Sincerely

    The Montana study found an increase in fatalities with an increase in posted speed limits, which is consistent with the conclusions made by similar studies.

  • Andrew

    No, you’ve mistaken the so-called “Solomon curve” (see wikipedia) with the “85th percentile” guidance for speed limits. One anti-85th%tile assessment notes: “there are references to the 85th percentile rule as far back as 1956 in an excerpt from Nation’s Business, a magazine from the U.S. Department of Commerce, in which the author J. Edward Johnston states: “Many traffic authorities agree that a limit which includes 85 per cent of the drivers is reasonable (Johnston, 1956)”. Certainly the 85%tile predates David Solomon’s publication if by 1956 “many traffic authorities” are advocating it.

    I haven’t mistaken anything, but nice job citing something even more outdated than Solomon’s 1964 paper. Research has progressed since 1956, outlooks have changed since 1956, and new technologies (such as automated speed enforcement systems) have come about since 1956. What made sense to “many traffic authorities” in 1956 has no bearing whatsoever on what’s appropriate in 2019.

    The 85th%tile reflects actual driver behavior.

    Yes, that’s tautological. It’s also meaningless. Laws, such as speed limits, are prescriptive, not descriptive. “Speed limit 30” means that motorists shouldn’t be driving faster than 30, not that motorists already aren’t driving faster than 30 – and if they don’t voluntarily comply, enforcement can persuade them to comply.

    If that’s unacceptable, then re-engineer the roads for the convenience of bicyclists.

    I’m sorry, what’s that you said? For the convenience of bicyclists? . (And it’s kind of cute how you forgot about pedestrians.)

    There is nothing wrong with considering the safety needs of pedestrians and cyclists in determining the most appropriate speed limit. There is also nothing wrong with enforcing the speed limit.

    That works; however, there may be unintended consequences:

    https://bikinginla.com/2019/01/21/vision-zero-is-not-a-fad-and-its-not-making-our-streets-more-deadly/

    But why bother with the facts?

  • Andrew

    I study

    You do nothing of the sort.

  • Andrew

    Not sure what your point is. In the absence of enforcement, on some roads drivers voluntarily choose to drive within the speed limit, while on other roads they don’t. Enforcement is what persuades drivers to drive within the speed limit even where they’d prefer not to; it has no effect where drivers are already complying with the speed limit.

    As I said: “if it isn’t adequately enforced, it’s as if the law doesn’t exist, and people act as they please.” Do you disagree?

  • Andrew

    I don’t know what an “urban thruway” is, but you’re the one who introduced it here, not thielges.

    So let’s consider two roads with exactly the same geometry, but one in a rural setting and the other in an urban setting with considerable pedestrian activity. If driver behavior is influenced primarily by road geometry, then drivers will behave similarly on the two roads. But, in fact, a speed fully appropriate on a rural road would be highly inappropriate on a geometrically identical urban road with pedestrian activity.

    That’s where speed limits, and enforcement of speed limits, come in.

  • Sincerely

    From the official report based on that Montana study you tried to cite elsewhere:

    “Operating speed models that have included posted speed limit as an explanatory variable have found positive correlations between posted speed limit and operating speeds (Aljanahi, Rhodes, and Metcalfe 1999; Figueroa and Tarko 2004; Jessen et al. 2001; Polus, Fitzpatrick, and Fambro 2000).”

  • DukeGanote

    The majority of citizen-motorists are reasonable and prudent; if the 50-mph limit is too low, they’ll ignore it. If it’s too high, they’ll ignore it. If it matches the road and traffic conditions, it’ll get good compliance without Orwellian oversight.

  • Sincerely

    You should really get with the times. The 85th percentile rule is based on flawed interpretations of flawed research, which has been pointed out to the extremists with the NMA many times. You are more interested in helping law-breaking motorists avoid accountability than you are concerned about the safety of road users.

    “The results showed a significant impact of posted speed limit on free flow speed.” — from “Prediction Models for Free Flow Speed on Urban Streets”

  • thielges

    Duke – I hope you didn’t strain your back moving those goalposts. It doesn’t matter what the road looked like a quarter century ago, we are discussing the state of the road now. Also you neglected to answer the one question I asked: “Where in that article does it imply that Whitehouse, OH placed those speed limit signs to harvest revenue?”. You are behaving like a troll and not someone with a cogent argument.

  • DukeGanote

    No strain at all; the term ‘ticket’ is twice in the article — once admitting tickets under 50-mph were issued. Just for fun, you can jump ahead a year and see what limits were set by ODOT in 2018 after study.
    https://nbc24.com/news/local/whitehouse-speed-limits-set-to-change-after-traffic-study

  • thielges

    Duke – awesome. Looks like a positive outcome for Whitehouse. The new gradual 50-45-40-25 MPH slowdown is better than the old abrupt 50-35 slowdown. The 50 MPH limit moves further east and lowering speed limits to 25 in center town improves safety. The net effect is to slow traffic down further through most parts of town. Both new and old are better than ODOT’s standard protocol calling for 50 MPH right through the town center, which might have been the 85% speed back before Whitehouse took safety into their own hands.

  • Sincerely

    So you’re presenting two options:

    1) Cities spend money they don’t have to completely eliminate speeding violations through very aggressive enforcement. (You ignore how much public backlash there would be.)

    2) We don’t enforce speed limits that would save lives. Oh well.

    There’s a third option, though, which is

    3) Do what we can, because every life has value. If cities can’t afford an enforcement blitzkrieg to eliminate law-breaking, that’s no excuse for not pursuing enforcement of speeds we know reduce collisions and fatalities.

    That you insist the reason cities don’t choose #1 is because of some infinite conspiracy to fleece people who drive reflects your own disregard for the safety of motorists, pedestrians, and other road users. Perhaps, instead, cities make the only choice they can, doing what they can with what they have.

  • DukeGanote

    It’s an excellent example of what happens when speed zoning is done by professionals rather than politicos. The village center was always posted 25-mph.
    https://tinyurl.com/WhitehouseOH25 ODOT never questioned the center’s conformance with Ohio Revised Code 4511.21 requirements.

    ODOT merely stated the law for “State Route 64 between Cemetery Road and Gilead Street” as of 1995. Actual 2018 study indicated sufficient development to warrant lower limits than 50-mph… but not to the 35-mph limits long and erroneously posted by the Village there.

  • thielges

    Right Duke, and just to return to the point that started this thread: there’s no indication that Whitehouse had posted that speed limit to collect revenue as you had asserted.

  • DukeGanote

    An “urban thruway” is as close as I could envision to thielges’ description; it’s essentially a rural road in the middle of suburbia; here’s one with an adjacent hike-bike trail. There is some pedestrian activity (I used to live nearby), but pedestrians-cyclists are segregated from motorized traffic except at intersections: https://tinyurl.com/Anderson5Mile

  • DukeGanote

    Cool; thanks for the bikingia rebuttal; I figured the WSJ op-ed was short on verifiable facts, and I figured someone here might have a rebuttal to review.

    Nonetheless, it’s possible to re-engineer roads for the convenience of cyclists and pedestrians; it’s frequently done in European cities. You’re assuming that “convenience” is a pejorative term.

  • jcwconsult

    Motorists should be able to drive as fast as they feel comfortable driving. The context in which they operate their vehicles is irrelevant. Drivers are only killing 40,000 people per year in the US, they are clearly safe and in no need of regulation.
    James C. Walker, National Motorists Association

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