Life (and Death) in the Fast Lane

I realize you don’t have the data in front of you, but hazard a quick guess. Which has received more media coverage: 9/11, Iraq, and Afghanistan combined; or the repeal of the nationwide 55 mph speed limit? You probably guessed the former. But there’s a good case to be made that the answer should be the speed limit. Why?

According to a recent paper by Lee S. Friedman, Donald Hedeker, and Elihu D. Richter, the lifting of the federal 55 mph speed limit in 1995 was responsible for 12,545 deaths between 1995 and 2005. That’s about 45 percent more American fatalities than we have suffered in 9/11, Iraq and Afghanistan put together. And all those human tragedies are due not to weighty national security imperatives but to the fact that we all want to go just a little bit faster.

The theoretical reasons for the increase in road deaths are pretty self-evident. At higher speeds you have to react more quickly and have less margin for error, making accidents more likely. Kara Kockelman of the University of Texas at Austin, along with Jon Bottom and other contributors, prepared a report on the topic for the Transportation Research Board (the gold standard of transportation bodies). It showed that being on a road with a 65 mph limit instead of 55 mph means a 3 percent higher probability of a crash taking place.

Much more significant is the fact that the extra speed makes the crashes that do occur far more deadly. Kockelman et al. estimated that the difference between a crash on a 55 mph limit road and a crash on a 65 mph one means a 24 percent increase in the chances the accident will be fatal. Along with the higher incidence of crashes happening in the first place, a difference in limit between 55 and 65 adds up to a 28 percent increase in the overall fatality count.

In addition to blood, the increased speed limit is costing us treasure. While the difference between 55 mph and 65 may not seem so large, the relationship between speed and fuel economy is highly non-linear due to engine design and the physics of wind resistance. A car that gets 30 mpg at 55 mph gets about 27.5 mpg at 65 mph and 23.1 mpg at 75 mph. Higher speeds thus mean greater fuel costs for motorists and more dependence on foreign oil. This was the reason the national limit was enacted in the first place.

Of course, higher speeds and reduced fuel economy mean more greenhouse gas emissions as well.

I must note there are doubters. Given that the imposition and subsequent revocation of the 55 mph limit is about as neat a natural experiment as transportation scholars are ever likely to get, there is surprising discord over whether the putative increase in the death rate has really occurred. See this from a skeptic (Robert Yowell).

And certainly other factors (like weather, DUI, law enforcement, seatbelt usage, demographics, driver education, driving while distracted, and car and highway design) are in many cases much more important than speed for accident and fatality rates.

But despite the disputes and qualifications, Kockelman’s study, which is the most comprehensive, does show that speed kills.

That said, let’s be honest. Even after reading this post, how many of you are going to close the Freakonomics tab, surf over to the U.S. Congress site, and write a passionate letter beseeching your congressman to bring back 55 mph?

Probably few of you — because there is, of course, another dynamic at play here: the thrill of speed and the allure of time savings.

None of the papers I’ve seen have calculated the economic benefits we derive from going faster, in large part because they vary so widely. (Benefit of high speed limit to driver on lonely rural highway: potentially large. Benefit to driver on congested urban freeway: zero).

But nevertheless the benefits are there. If cancer researchers can save a few minutes a day on their commutes, some of that time will go to finding a cure for a dreaded disease.

Plus, going faster is fun. I admit I like it, and I don’t even like driving.

On the other hand, the speed benefit may be surprisingly small. Kockelman et al. found that a road with a 65 mph limit sees actual traffic speeds only 3 mph faster than a road posted 55.

Is the trade-off of safety for speed worth it? This may be more of a question for a philosophy professor than a transportation scholar. But there is one point I feel strongly about. Even if the effects of the higher speed limits are very small, as skeptics believe, the disappointing thing about this debate is that it is conducted on the pages of a handful of obscure academic journals and the occasional newspaper article on page B12, as opposed to front and center in the public eye.

Even though partisans on either side of the political spectrum sometimes take the position that every human life is priceless and cannot be sacrificed no matter what the circumstances (the left wants to abolish the death penalty; the right wants to abolish abortion), politicians of all stripes make decisions that take human life all the time, often with little scrutiny. The issues surrounding automobility are an important example. In this case, it might be nice if we slowed down and gave these questions the focus they deserve.

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  1. jroane says:

    Also never debated is the consistent increase in horsepower in most cars. Why do we allow production of personal vehicles capabable of going over 100 mph? Is there really any reason to have a personal vehicle with the capability of going faster than, say 70 mph? Reduction in horsepower could both save lives and reduce gasoline consumption.

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  2. Casey says:

    I have been reading acticles every change I get on this subject and this one has been one of the best. I consider, and try on occasion, to drive slower on the freeway, but more often than not, the speed winso ut over the thoughts of saved gas a less risk. One thing I never do see addressed in any acticle on this subject is that a 55 mph speed limit means everone is driving 65 and a 65 limit has everyone going 75 or 80 and more. So the reality is that having a 65 limit means everyone drive 75 and putting the limit back to 55 would mean everyone drive 65. I would think this reality would have to be addressed more clearly if what you conclude in your acticle, and I agree should happen. Set the limit back or not, but lets have a serious discussion and study and give this issue the focaus it deserves. Cheers.

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  3. Chris Rider says:

    So if on average a 65 mph road sees only 3 mph more than a 55 mph road, then 12,000+ deaths are caused (or linked to) a 3 mph speed increase? Seems odd to use data that indicates a small speed benefit to argue for reinstating a stricter speed limit when the primary argument is that extra 10 mph is the real problem…

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  4. Terry says:

    Sure a few lives will be lost…but millions will be late!

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  5. MikeM says:

    I have a personal rule: if I’m ACTUALLY in a hurry and need to get somewhere (say, work) on time, I might drive in the fast lane. But all other times I head for the right lane and only pass when vehicles are going below the speed limit. It is actually quite relaxing and the psychological and physiological benefits to reduced stress far outweigh the benefits of getting somewhere quicker.

    Also, I never ever ever use the phone or text while driving.

    @jroane: One benefit to horsepower is the ability to accelerate quickly. This could potentially help in avoiding a sticky situation or even an accident. But you’re right in that this probably doesn’t outweigh the consequences of excess horsepower.

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  6. Mars90 says:

    Why is 55mph the magic number? Lowering it to 40-45mph would probably maximize fuel efficiency for most cars and would have even fewer accidents and fatalities than 55mph. But 40-45mph on expressways is ridiculously slow, right? Well, some people feel that way about 55mph, too.

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  7. Jeff W says:

    I imagine than an important factor in people’s lack of concern about speed limit gets back to the idea of “cause.” Let’s say you’re driving along, something goes wrong, you crash and die. Is it because Congress raised the speed limit? Because highway engineers built a road that seemed like you could drive fast on it? Because you’re a bad driver? Etc.

    I think we instinctively seek out proximate causes for individual incidents, and distal causes for events in the aggregate. Of course, we’re all much more interested in individual events, namely am I going to make it to seder without crashing? So we look for proximate factors, such as my (excessive) faith in my own driving ability.

    So here’s the risk/reward equation for a higher speed limit. Benefit: some other people that I’ll never meet will live longer. Cost: I take an extra hour to get where I’m going.

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  8. CK says:

    I thought most research said without heavy enforcement vehicle speeds reach their own average unaffected by speed limits, No?

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