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.


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.


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.

Chris Rider

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...


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


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.


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.

Jeff W

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.


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


The comparison between the speed limit and 9/11 and the wars in Afghanistan and Iraq make my head hurt. Obviously you're comparing different lengths of time, 1995 to the present vs. two events that started 2001 and one in 2003. Second, the population at risk for being killed while in a car is far, far greater than the one at risk for being killed in Iraq and Afghanistan. There are arguments for lowering the speed limit, which are discussed, but trying to make driving 65 MPH seem as dangerous as fighting two wars is ridiculous.


Well, if the difference between 55 and 65 is 12,500 deaths over 10 years, clearly even more lives could be saved with a national speed limit of 45, 35, 25, or even 10 mph. Imagine how safe our roads would be!

It's disingenuous to pretend that 55 is a baseline with zero fatalities, and going to 65 adds some number of deaths. The reality is that there is a tradeoff of permitted speed versus acceptable accidents and fatalities. We can debate what that tradeoff is, but anyone who claims that the only measure that matters is fatalities should be pepared to support 10mph, or lower, limits.


Good catch Chris! That was going to be my point to. Which is it? With a higher speed limit we drive faster, which is dangerous. Or is there really is no difference in speed anyway?

I want to know how many more tickets have been written per highway mile driven since the change. I think a lot of it has to do with the financial gain than safety, a la red light cameras.


I can't drive 55 :(

Chuck Andrews

It's a sobering fact that speed kills and today's politicans have long forgotten their role as "representatives of the people". Arriana Huffington's first book club recommendation should be must reading for those interested in changing our nation's attitude about speed. The book is: "In Praise of Slowness" by Carl Honore.



Actually 55 mph is the magic number (approximately, the true 'magic number' is slightly different for each vehicle). The fuel efficiency graph is shaped like a bell-curve in that going 5 mph is extremely inefficient (you're stuck in 1st gear) and going 95 mph is extremely inefficient (you're facing extreme air resistance).

If you want to find the most efficient speed for your car, get on the highway (preferably a flat, straight stretch), get into your highest gear, and then find the lowest RPMs you can steadily maintain while in that gear. This won't be the scientifically determined magic number that you could get in a wind-tunnel, but it'll be pretty close to your cars sweet spot.

As for the article, I find it interesting that the supposed cause is higher speeds requiring faster reflexes and less room for error, but then we're told that the difference between 55 and 65 highways is a real-life speed difference of only about 3 mph. The difference in reflex time and room for error between any two speeds that are only 3 mph apart is going to be negligible.



Gotta agree with #3, Chris Rider, on this one.

By your earlier numbers, a 3mph increase in actual driving speeds means a 7.2% increase in the chances an accident will be fatal. Add that to your 3% higher probability of crashes occurring (now 0.9%), and we have an increase of just* 8.1%. Hardly the 28% used in the post (which should be 27% (24 +3), right?).

*I say 'just' because any increase in traffic deaths is of course a sad thing



You make a good point, we're all making trade-offs here... you could even argue that the safest thing to do would be to ban all cars. But then you'd have resulting deaths from health problems while walking (off-set by the health benefits of the entire population walking more?), deaths from people getting lost in the wrong part of town and taking 45 minutes to get somewhere safe (instead of 5 minutes of driving), etc.

On a financial note... can you imagine how much money we'd save if we weren't paying for cars, paying for gasoline for the cars, paying for expensive highways, paying for extended trips made easier by cars, etc... but then of course we'd be a third-world country in no time.


I suspect that if we had a gas (or carbon) tax that was appropriately priced to account for all of the negative externalities of driving, a 55mph speed limit might seem more attractive.

Tom G

Mars90, actually 55 is about the magic number, for some cars 40 is slightly better, but after 55 the dropoff in fuel efficiency accelerates

Make the speed limit 55, give speeding tickets much more frequently, but keep the fines in line with parking violations. That would keep drivers at the correct speed


Let's see...
Stay in the right lane as much as possible.
Avoid driving between 10 PM and 4 AM.
No Cellphone usage.
Eyes on the road at all times.
Keep your distance with the car in front of you.

I bet these steps improve your safety by 50%.


The graph of approximate gas mileage vs time that I get in my Prius serves as a powerful and immediate incentive to drive more slowly, leave more following distance (so I can coast more and not constantly be braking and accelerating) etc. It gives me pleasure and satisfaction in driving with greater efficiency, which I think is also a safer way to drive. If such a meter was installed in most cars, I think habits would change, we would have lower gas usage and safer roads.