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.