Study: Lowering the Speed Limit … Works To Reduce Speeding

Photo:  IIHS
Photo: IIHS

Here’s some encouraging news for cities trying to reduce speeding: New research from the Insurance Institute for Highway Safety shows that lowering posted speed limits appears to be effective at reducing driver speeds.

The IIHS study compared speeds before and after Boston lowered its speed limit from 30 mph to 25 mph in January, 2017 — and the results were clear: “Vehicles exceeding 25 mph, 30 mph, and 35 mph all declined at sites in Boston, with the largest reduction in proportions of vehicles exceeding 35 mph,” wrote the study authors Wen Hu and Jessica Cicchino.

In fact, the odds of a Boston driver exceeding 35 miles per hour after the speed limit change decreased 29 percent and that a driver would exceed 30 mph declined 8.5 percent (the study offered “odds” because it tracked speeds at specific sites rather than following the same drivers before and after the change).

The study did not examine the impacts on crashes, but prior research shows that slower speeds reduce collisions, said Hu and Cicchino.

IIHS President David Harkey said in a statement that the study should encourage other cities to adopt lower speed limits to reverse the dramatic increases in pedestrian fatalities that have occurred over the last five years. Cities like Seattle, Portland and New York that have lowered their speed limits in recent years.

Two Boston City Council members — Ed Flynn and Frank Baker — have proposed lowering speed limits in the Hub even further, to 20 miles per hour.

70 thoughts on Study: Lowering the Speed Limit … Works To Reduce Speeding

  1. As I view our activities, I see mostly attempts to block the loss of existing vehicle lanes from the main collector and arterial streets – not the addition of new ones. These are the streets designed to carry the majority of vehicles for commuters, shoppers, tourists, visitors, and commercial traffic. There are significant negatives that result from choking down those arteries.

    We usually would support the addition of new lanes on suburban and urban freeways when congestion gets too high – but that can usually be accomplished within the existing rights of way.

    James C. Walker, National Motorists Association

  2. Right. And wholly disregard infrastructure for anyone using public spaces outside of the private automobile. Therein the problem.

  3. I have spent a lot of time in Europe, licensed for 58 years with 1.1+ million miles of driving in 27 major world countries. Many areas in Europe separate cyclist traffic from the main roadways on the collector and arterial streets that are the necessary arteries for commerce. Many areas in France have separate bike and pedestrian lanes marked on the sidewalks, as did Berlin. The best example I saw was in Reykjavik, Iceland with a 2 lane bike path on the sidewalk that had pedestrian crosswalks across the 2 bike lanes in areas where pedestrians would go to cross the parallel roadways and even where they needed to cross the 2 bike lanes to get to a bus stop.

    It is unusual in most of the USA to have cyclist traffic be more than about 5 or 6% of the flow. That does not justify ~25% of the roadway surface.

    James C. Walker, National Motorists Association

  4. Back to the data: In cities where cyclists are 5% of users, how much of the pavement is given to them? You have a windshield perspective. That is your calling card but it keeps you from seeing the whole picture transportation systems suffer due to your activities and lobbying.

  5. An existing main four lane collector or arterial where the proposal is for 3 vehicle lanes plus bike lanes would devote 25% of the roadway surface to cycles – a change far out of proportion to the actual or even likely future usage.
    Bike lanes on the roughly parallel non-collector and non-arterial streets are a GOOD idea because it separates most of the cyclist traffic from the vehicle traffic. That benefits everyone.
    James C. Walker, National Motorists Association

  6. See, this is what I mean: bad faith argumentation. Again, in a city where 5% of mode is cyclist, what is the TOTAL percent of pavement reserved for cyclist? Not a road, the system.

  7. The conflict of use issue is on the main, usually multi-lane, collectors and arterials that carry the bulk of the traffic from commuters, shoppers, tourists, visitors and commercial vehicles.

    If someone does understand that differentiation from more minor streets that are not designed for the heavy traffic flows, then they need to study more about traffic flows and commerce needs. It is not bad faith to want commerce to be supported and to be willing to dedicate more bike lanes on more minor streets that are roughly parallel to the main collectors and arterials.

    James C. Walker, National Motorists Association

  8. So, ‘not 25%’ is what you’re admitting to in the words above? That’s all I was really interested in. The flowing oratory in support of car supremacy isn’t necessary at this point.

  9. I think it is time for us to quit. Many of your questions and comments were thoughtful and realistic – and I tried to supply answers in the same vein.

    Engineers and officials must take commerce into account in planning traffic patterns for people and vehicles that come from distances & directions where walking, cycling or using transit are not practical alternatives. If that is not a reality for you, then my answers will be meaningless to you.

    Thanks for many items of good discussion.

    James C. Walker, National Motorists Association

  10. Ticket cameras are illegal in several states

    Again, your organization is a lobbying group trying to change laws. Have the honesty not to pretend you believe that the existence of a law on a subject is itself compelling evidence of how things should be.

    They are always sold as for-profit partnerships

    There’s no reason that has to be the case. They could be run by cities, at a loss, just like most other law enforcement is.

    It’s notable that you aren’t trying to lobby for restrictions against the profit models that can be used, but instead want them to be completely illegal, and try to convince people that they don’t do anything (despite a variety of studies that show that they do, in fact, reduce speeding and injury accidents).

    Because the truth is that while you are trying to position yourself as being against the profit motive, what you are actually against is anything that would slow down motorists.

    you must degrade the roadways

    Saying that you consider engineering changes that reduce motorist speeds to make things safer for everyone “degrading” the roadway is one of those things that make it crystal clear what you and the NMA are actually about.

    (Also, by the way, stating your belief that it’s impossible for enforcement to effect changes in behavior as “reality” does not, in fact, make it reality. A variety of automated speed enforcement systems, in a variety of countries, have demonstrated changes in behavior. The fact that this doesn’t support your narrative doesn’t make it untrue. The fact that more expensive and invasive solutions work better doesn’t change that either.)

  11. Agreed, ticket cameras could be owned and run by cities without involving for-profit companies – and/or could be supplied by the for-profit companies but run with substantial financial losses by not ticketing mostly safe drivers. It just isn’t likely to happen. I have been in one city council meeting where the for-profit companies made their overall sales pitch, and have knowledge of many other instances to understand how they are sold. And the reality is that ticket cameras supplied by the for-profit companies must ticket mostly safe drivers or the total fines won’t even pay the cameras costs.

    Example on the roadway design: If a main multi-lane arterial or collector street operates with an 85th percentile of 41 mph – meaning the slowest 85% of the drivers feel safe and comfortable at speeds up to 41 mph – and you want the slowest 85% to feel safe and comfortable only at speeds up to 25 or 30 mph, then you have to degrade the roadway environment to achieve that.

    Results in some foreign countries with vastly different cultures are often not importable to the US.

    James C. Walker, National Motorists Association

  12. It just isn’t likely to happen.

    Says the lobbyist trying to make sure it doesn’t by pushing for making them completely illegal instead of regulated to prevent abuse.

    must ticket mostly safe drivers

    You keep saying “mostly safe drivers” as if that’s a meaningful concept when talking about people who are speeding. If Boston has decided that the speed limit should be 25mph for safety reasons, then a driver going faster than that isn’t “mostly safe”. They are speeding—dangerously, according to the community that decides what level of risk they are willing to accept from cars.

    Every driver I know who speeds claims that they speed “safely”. I’m sure the ones who hit pedestrians while speeding were firmly convinced they were being safe right up until that moment (and many of them probably afterward too), but physics doesn’t actually care what the driver believes.

    (I’m sure you’re going to try to counter with some examples of obvious speed traps. If you want to lobby for laws that prevent clearly malicious speed traps, knock yourself out; I doubt many safety advocates will have a problem with that. But you’re also trying to make it illegal for them to be used around schools, and in urban cores with high pedestrian volumes, where there is a clear and legitimate societal interest in controlling speeds.)

  13. Sadly, that research has led to the terrible mess on American streets today. you should travel more, say to Northern Europe. It would open your eyes.

    Funny thing, when I was applying to be an exchange student to Germany in the early eighties I told a group of professors at UT Knoxville that they had separate signals for bikes and other improvements in Munich which showed a completely different attitude to pedestrians, meaning they thought streets aren’t just for cars. They literally laughed at me, including a Civil Engineering professor.

    Now thirty five years later they have implemented some half-assed improvements on Cumberland Avenue near campus. Check it out. It’S still pretty bad, but at least they acknowledge the heavy pedestrian traffic. America is literally forty years behind in street design. The result is tens of thousands of avoidable deaths every year., thanks to the criminal negligence and victim blaming of people like you

  14. If the 85th percentile speed is 31.0 mph per the study, then the safest limit to post (with no engineering changes) is 30 – not 25. The fact the 85th percentile speed remains 31.0 makes the point quite clearly. That is the science, now at least 77 years old that I can show in writing.

    If it were possible to regulate speed and red-light cameras to prevent abuses, the industry would cease to exist with no profits.

    Your comment above: “If Boston has decided that the speed limit should be 25mph for safety reasons, then a driver going faster than that isn’t “mostly safe”. ” Arbitrary limits not supported by the science are just that – arbitrary, and please note from the study – totally ineffective.

    James C. Walker, National Motorists Association

  15. I agree there are many things that can be done with engineering. Separate bike signals can help, so can advanced WALK signals by a few seconds for pedestrians. I have driven extensively in Northern Europe starting in 1972 in Sweden. Many areas in Europe have bike lanes totally separated from the vehicle lanes. I don’t blame the victim, but I do quote the NHTSA data on pedestrian contributions to their crash rates. Safety takes responsible behavior from drivers, cyclists, AND pedestrians.

    What does not work is under-posted speed limits and red-light without correct engineering changes – enforced enough for profits, but not enough to materially change the speeds or violation rates. That is the USA today, and it is wrong.

    James C. Walker, National Motorists Association

  16. Best-practice engineering will do better than any ticket camera. Also, how many people avoid camera areas, so how is that counted?

  17. Translation: Everybody needs to strictly obey the law! Except that drivers of course get to ignore the actual law and replace it with whatever they wish.

    Am I close?

  18. No, and sarcasm adds nothing useful to the discussion.

    James C. Walker, National Motorists Association

  19. If everyone voluntarily complied with traffic laws regardless of how arbitrary and improper they were, none of the controversies would occur. For the real start of nationwide conversion of laws and enforcement from safety to profits – look at the 55 mph limit applied to freeways from 1974 to 1987, and eased to 65 from 1987 to 1995 when the counter-productive National Maximum Speed Limit (NMSL) was finally repealed. Authorities and the insurance industry jumped on those improper limits (“speed kills”) and used enforcement for massive profits that came mostly from the safest drivers on the roads – the ones near the actual 85th percentile speeds with the smallest statistical risks to be in crashes. The NMSL changed the entire character of enforcement from safety to profits – and the change rapidly expanded to rural highways, county roads, and urban collectors & arterials. When “10 over” tickets are given to drivers in speed traps where the posted limits are set 10 under the actual 85th percentile speeds, those $100-$200 tickets and the often-resulting $300-$500 insurance surcharges go to the safest drivers for the dastardly crime of driving safely for the conditions. It is a racket, and all wrong.
    James C. Walker, National Motorists Association

  20. This study conflicts with my deeply held beliefs, I refuse to acknowledge it.
    James C. Walker, National Motorists Association

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