How Can Higher Speed Limits Save Lives

Before your blood pressure start to go off the chart dear colleague, have a careful look at what Dr. Aaron Carroll, also known as the Incidental Economist, has to say on what may appear to be a counterintuitive approach to our favorite topic (or at least one of them) speed and safety.

Thanks for the reminder Aaron that in our complex field, things are not always what they may at first glance appear to be. One thing for sure: a street is not a road (but then you knew that when you were preparing this little mind trap and wake-up call).

Sometimes Faster is Better

– Aaron Carroll. Indiana University School of Medicine

In the past episodes I have talked about how accidents are the number one killer of children, and so car accidents represent a fairly large part of accidents in general. In response, the number of you asked me why we do not reduce the speed limits of many roads nationwide in an attempt to bring that number down. I am glad you asked. That is the topic of this week’s Healthcare Triage.

Those of you who want to read more and see references can go

More from the author on speed and what he is actually saying:

As promised, I addressed a lot of your questions in a blog post this morning. Go here to read it:
Here is the text:The video brought out a lot of great questions in the comments. Enough that I think it’s worth a follow-up post to address some of them. I’m paraphrasing them. Here we go:1. There are studies showing that people who drive slower are less likely to die than people who drive faster. Doesn’t that bother you?
Well, sure. But a lot of those studies are showing that people who drive less than 30 mph are less likely to die than people going 40 mph. I’m sure people going less than 10 mph are going to die even more rarely. If we don’t drive at all, it will go down even further. I’m not disputing this fact. We accept a certain amount of risk when we drive.

But this video wasn’t about speed – it was about speed limits. The question is whether a 55 mph speed limit is always safer than a 60 or 65 mph speed limit. That’s not as clear.

2. How can you advocate for higher speed limits (of even 65 mph ) in a city?
I don’t!!! We’re talking about highways here. I said that I don’t think we should do away with regulation. Residential areas, school zones, those are a whole other story.

3. Aren’t you cherry picking by citing Lave? Doesn’t other research show that lower speed limits reduce fatalities?
I tried not to cherry pick. But you’re misinterpreting me. I take the fact that the literature is equivocal on this to mean that there are probably times when slower speed limits are better and times when faster speed limits are better. I’m not advocating for higher speed limits across the board. The point of the video was to push you to question your bias that slower is always better. Sometimes (not always), faster speed limits may be better.

4. Aren’t you advocating that people break the law here?
Nope. I’m advocating that we should sometimes change the law because people not following it is leading to a bad outcome.

4a. Isn’t that really saying that people shouldn’t be held accountable for breaking the law?
Nope. I think people should follow the law. But sometimes, in the real world, they don’t.

4b. Shouldn’t we just punish them?
This is a critical point, and worth of debate. I view this as the difference between efficacy and effectiveness. In an ideal world, everyone would do what we tell them perfectly, and we’d get the “efficacy” of speed limits. In the real world, lots of people don’t, and you see the “effectiveness” of speed limits. The effectiveness is often much less than the efficacy. If we can’t change the world to make efficacy work, we should deal with effectiveness. Sometimes, that means raising a speed limit. We’re not doing it to benefit lawbreakers. We’re doing it potentially to prevent accidents and save lives.

5. Shouldn’t we listen to engineers who tell us what the speed on a road should be?
YES! That’s exactly what I said in the Route 3 example, where engineers rated the road much higher than 55 mph. Looking back at effectiveness, it turns out that people may be, in general, pretty decent at figuring out intuitively what a safe speed on a road would be. If you set the speed limit near that number, more people drive the same speed. If you set the speed limit too far below that, you get a lot of people driving at different speeds. I’m advocating for listening to the engineers.

6. What about pedestrians?
Pedestrians shouldn’t be on highways!

7. What about animals?
I have no data on that. But I have to say that almost all highway laws are about protecting humans, not animals.

8. Why do you focus on the US?
I use the US as an example. I live there, and I know its policies best.

9. Traffic cameras could fix all this!
Maybe. But they’re not in use like that in the US, and if they were, maybe the evidence here would be different. They are, in their own way, an attempt to improve efficacy, by making more people follow the law. That’s another option, but perhaps expensive. And not everyone will tolerate monitoring.

10. Don’t improvements in cars reduce fatalities and accidents? How do you know it’s not that, but instead speed limits?
We don’t. I think they’re absolutely reducing fatalities. Accidents, to a lesser extent. But these are responsible for both better outcomes with lower and higher speed limits, and people on both sides use them to bolster their claims.

Let me finish by repeating what I said in the video. Sometimes we have to question our biases for the real world. There are times when lower speed limits are better. But there may be times when higher speed limits are better. NOT ALWAYS. But sometimes.

* Reprinted with permission of and thanks to the author. Original YouTube video at

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About the doctor:
aaron carrollAaron E. Carroll, MD, MS is a Professor of Pediatrics and Assistant Dean for Research Mentoring at Indiana University School of Medicine. He is also the director of the Center for Health Policy and Professionalism Research. He earned a BA in chemistry from Amherst College, an MD from the University of Pennsylvania School of Medicine, and an MS in health services from the University of Washington, where he was also a Robert Wood Johnson Clinical Scholar. He is also the co-author of Don’t Swallow Your Gum: Myths, Half-Truths, and Outright Lies About Your Body and Health, published by St.Martin’s Press.
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Where does that leave us on our program to bring down speeds significantly on the streets of our cities?  pretty much where we started , but  more cautious about  are thinking and recommendations  but being  more aware of of the complexity  of the behavioral issues  in addition to that of the importance of the architecture.

Eric Britton
9, rue Gabillot, 69003 Lyon France

Bio: Trained as a development economist, Eric Britton is a sustainability activist, mediator, MD of EcoPlan International, an independent advisory network providing strategic counsel for government and business on policy and decision issues involving complex systems, social-technical change and sustainable development. Founding editor of World Streets and Distinguished Professor of Sustainable Development, Economy and Democracy at the Institut Supérieur de Gestion his latest work focuses on the subject of equity, economy and efficiency in city transport and public space, and helping governments to ask the right questions and in the process find practical solutions to urging climate, mobility, life quality and job creation issues. More:

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One thought on “How Can Higher Speed Limits Save Lives

  1. I’ve heard that doctors are the worst pilots because they are over-confident. Save a life or two and that confirms one’s chosen-ness. Speed limits are set because our judgement is so poor.
    In transport you can either have access or speed, not both at the same time. The limited access road – U.S. Interstate, is a limited access road network which enables speed. Were it built and managed like the modern German Autobahn, it could handle higher speeds – all in the company of experienced drivers. This is demonstrated in the racing sports. When city streets are used off-peak for racing, tragedies result. This thesis is a waste of time and energy. Instead of wanting to drive at a higher speed to get to your important event, just leave earlier and take into account the likely traffic conditions of the day.


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