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.

s g

It's no use blaming the politicians because they're just doing our bidding. If you polled people, a majority of them would not want to drive at 55 mph. After all, how many people do you know that don't blame the cops or the legal system when they get a ticket. The problem is with human nature. The average person would love for these laws to be enforced...on every person other than himself.

Hannah H

I wonder how a rise in the speed limit will (if at all) affect productivity? I should think it would rise if trucks can reach their destination quicker. But then again, higher fuel costs might offset any production savings. Is there any data on this?

Aaron V

Of course another factor to take into consideration would be any changes in driver education if applicable. Likewise, a comparison between the autobahn and US highways accident and death rate would be interesting to see.

Dumb actions are what kills people, speed just helps them. I'd rather stricter driver license requirements and a driver education system that actually works versus slower roads.

Mike B

I think there is another hidden factor at play and that is that police presence on the highways has markedly decreased on our Nation's highways. While the number of miles traveled have increased, the number of police officers devoted to making traffic stops has decreased. The article I read said that the chance of being pulled over for the same infraction has actually decreased by 20% over the last 10 years.

The route I travel in the morning and afternoon peak periods is signed for 55, but there is a complete absence of police patrol during those periods and had been for some years now. I believe this is intentional as often congestion is the limiting speed factor and pulling people over during the rush hours creates traffic jams. Anyway, I am upset if congestion LIMITS me to 65mph on this 55mph highway and 70-75 is the speed I feel safe traveling at.

Faster speeds are a natural result of progress. Cars have far better performance than they did back in the day and they are also much after. If one wants to decrease the number of fatalities perhaps other bars should be raised, instead of performance being watered down. In Germany, where some speed limits are only imposed by physics, obtaining a driving license is a difficult and expensive proposition and enforcement is rigorous so only the truly qualified drivers are out on the highways.

Frankly I am glad this is a debate that has been kept out of the public spotlight because given the level of public discourse lately I doubt anything good would come of it.


Scott W

How does this data jibe with Montana's?

This is the problem with only looking at the big (Federal) picture: you miss the small wins all over the place. Most of the Western states, where you have long stretches of rural highway, have seen a decrease in fatalities since the law was repealed.

Perhaps if the states were allowed to set their own limits... but that's crazy talk.

Michael B.

Now imagine a world where bicycle commuting is the norm. :)


"It's a sobering fact that speed kills and today's politicans have long forgotten their role as "representatives of the people". "

Funny, I thought my reps were fulfilling their role when they raised limits like I wanted.


Sure, if we all drive @ 5 mph, just think how safe we'll be. I'll have to disagree that speed kills. Driving too fast for conditions kills. If speed killed, there wouldn't be any Italians or Germans left. They drive one hell of a lot faster than we do, with fewer accidents.
I could, if it were legal, ride my motorcycle along I-80 all day long at 120 mph and never have an accident.
Our country (USA) has some of the most lenient driver/operator standards in the world. If we were all professional drivers, as they are in Japan, and if the barriers to entry into the driving world were far more difficult to hurdle, our roads would be far safer.
Speed has nothing to do with accidents. That's why they call them accidents.


I'm a staunch conservative, but I give Jimmy Carter props for seeing the importance of the 55 mph speed limit.

Not only did it lower American consumption of fuel, but it saved lives.

I remember how I chaffed going "just" 55. Even today, I have no problem with people on those long, empty stretches of Montana doing 90 mph, if they so desire. But on most interstates, 55 mph would STILL be a good idea. It would (again) lower fuel consumption and save lives.

I remember that only reason we repealed the 55 mph (under Reagan) was some cowboy notion of it limiting our freedom in some way. It didn't have anything to do with reason or so forth, just some vague notion of "driving faster is more American."

The longer Jimmy Carter has been away from office...the more I kind of wish he were back. He certainly is more impressive in HONEST retrospect than he was while in office. That's our loss: Republican, Democrat, American.



Back in the day when 55 mph was the standard I commuted 60 miles each way .

One week I decided not to exceed the 55 limit. My experiment lasted two days. I have never been so frightened while driving. I drove the inside lane of a 3 lane interstate and continually had tailgaters, horn honkers and finger-givers around me. Not to mention 18 wheelers and other assorted large vehicles.

I'm not aware of the research CK above mentions but I support the hypothesis. I am much more comfortable "going with the flow" than I was trying to obey the law.


Other factors have to be taken into account such as how many more drivers had been added since 1995, how many accidents were caused by using cell phone, etc. We know that cell phone users shot up during that period.


Tim, I'd also debate the ability to react any differently at 65 than at 95. We're speaking milliseconds, probably.
And, I'm afraid that stating in this article that 10mph has caused an additional 12,545 deaths is very misleading.
How many more drivers, how many more miles were driven, are the cars we're driving ten years after the study began smaller and possibly less crash-worthy? I'd guess the number of people talking on cellphones has increased exponentially in that same span! There are so many variables that could, and should be discussed regarding these deaths.


Outlaw motorists and all motorists become outlaws.

Although this report does provide some valuable statistics, it doesn't take a genius to figure out that slower driving will reduce the number of accidents and the number of deaths while driving.

The best way to reduce deaths is to reduce births because if you haven't been born you can't die (but maybe I'd need some money to study this). Reducing births has the added side affect of reducing deaths from of all causes not just those on rural interstates. Just think of all the money we'd save on funeral expenses alone.

The best way to reduce births is to ...

neil wilson

Am I crazy or is it a stupid waste of time to save MONEY by going slower.

Assume $3 a gallon gas and 100 mile trip.
30MPG at 55 costs $10 (100/30*3) and takes 109 minutes (100/55)
23.1MPG at 75 cost $12.99 (100/23.1*3) and takes 80 minutes (100/75)

So, to save 29 minutes you would spend $2.99 more in gas. That works out to $6.16 an hour after taxes. If you have two people in the car then it is even less.

This doesn't take into account the value of a life or the cost of an accident.

It is just stupid to drive 55 to save gas.


MikeM@5 "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."

I suspect that higher horsepower correlates strongly to a higher accident rate. Anyway, I doubt that faster acceleration is useful in the majority of cases of avoiding accidents (braking is probably much more frequent and useful).


They also aren't considering the increase in miles travelled the higher speed allows. What is the change in rate per mile travelled?

How much capacity do we gain with higher speeds?


Mars90@6 "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."

Because it's actually about right. It seems the peak fuel efficiency for most cars is about 55mph.
If there was no atmosphere, the peak efficiency would be a very high speed (as long as you had enough gears). Much, much higher than 55mph. This efficiency curve along with the aerodynamic resistance curve end creating a peak at about 55mph.


Germans on the Autobahn must die in the hundreds of thousands, then, right????


Brett@14 "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)."

Ignoring aerodynamic resistance, the amount of energy to keep the car moving at a constant speed is largely independent of that speed. That means the faster you go, the more efficient it is. If you had a constantly variable transmission (to keep the engine at a single, most efficient RPM), the efficiency curve would probably be nearly linear (ignoring aerodynamic resistance). Since cars typically don't have an infinite number of gears, the efficiency curve has bumps in it.

Since aerodynamic resistance isn't linear with speed, it causes slope of the efficiency curve to flatten out as speeds increase, peaking at about 55 mph and declining at faster speeds.


Mike B@24 "Faster speeds are a natural result of progress. Cars have far better performance than they did back in the day and they are also much after. If one wants to decrease the number of fatalities perhaps other bars should be raised, instead of performance being watered down. In Germany, where some speed limits are only imposed by physics, obtaining a driving license is a difficult and expensive proposition and enforcement is rigorous so only the truly qualified drivers are out on the highways."

One issue is that higher speed limits don't improve the average speed very much.

Why is "progress" necessarily "faster speeds" anyway? Why can't "progress" be "more efficient"?

The high speed limits in Germany are actually imposed by the car you drive (and how much you spend for it). That is, "high speed" travel in Germany is largely a privilege of people who can afford expensive cars. I suspect that the "no speed limits" on some sections of the Autobahn exists mostly for tradition and tourism, not because they make sense for safety, congestion, or efficiency.