Are higher speed limits linked with more accidents and more deaths on the road?

Nearly 45 years ago, President Nixon signed into law the National Maximum Speed Limit, a mandate that put the maximum speed limit in the United States at 55 miles per hour (mph). At the time, it was an attempt to curb gasoline consumption in response to the 1973 oil crisis, but many have argued the laws also helped improve highway safety. A little over two decades ago, the law was revoked, and since that time, speed limits across the US have climbed higher and higher.

As the above chart demonstrates, every single state now has roads with speed limits higher than 55 mph, and 41 out of 50 states have raised their maximum speed limits to 70 mph or more on some roadways. And because everything is bigger in Texas, the state boasts the fastest top speed limit with an 85 mph stretch on State Highway 130 between Austin and San Antonio.

While the average American certainly appreciates being able drive a little faster to get to their destination more quickly, many safety advocates believe raising speeding limits has come at a cost. When Texas increased its maximum speed limit to 85 mph, it drew many critics, including the Governors Highway Safet Association and American Trucking Association. Insurance Institute for Highway Safety (IIHS) spokesman Russ Rader stated that, “the research is clear that when speed limits go up, fatalities go up.”

Is that truly the case? Is the research really that clear? Are higher speed limits linked to higher rates of fatal accidents?


The Average Speed Limit in Each State

average speed limit in each state

source: Governors Highway Safety Association; average is for rural, urban interstates, and limited-access roads

To get a better idea of how speed limits can affect the rate of fatal accidents, it’s important to look not just at a state’s maximum speed limits but also it’s average speed limits across its different major roadways — rural and urban interstates and limited-access roads. This gives us a better idea of how fast a state’s roads are throughout.

More than two-thirds of states have an average speed limit of 65 mph or higher across these roadways. Only 6 out of the 50 states — Alaska, Vermont, Delaware, Hawaii, New York, and Rhode Island — have average speed limits below 60 mph.

Not surprisingly, Texas, which has the fasted speed limit on any single highway in the country, also has the top overall average speed limit — 78 mph — across its roadways. But its lead is a slim one, as South Dakota and Idaho both have an average speed limit of 77 mph on its major roadways.


Do Faster Speed Limits Lead to More Deaths?

speed limits death rate

Analyzing crash data from the IIHS, we found that, for the most part, states with a higher average speed limit across their major roadways also have higher rates of fatal crashes.

As demonstrated in the chart above, in states where the average speed limit is between 55 to 59 mph, the average number of crash deaths per 100,000 population was 8.7, making these states the least deadly for driving. This number climbs to 10.4 deaths per 100,000 in states with average speed limits between 60 to 64 mph, 13.4 deaths per 100,000 in states with average speed limits between 65 to 69 mph; 14.6 deaths per 100,000 in states with average speed limits between 70 to 74 mph; and 13.7 deaths per 100,000 in states with average speed limits of 75 mph and above.

In other words, drivers in states where the average speed limit is between 70 to 74 mph are 68% likelier to die in an auto crash than those in slower states with an average speed limit ranging from 55 to 59 mph.

These findings are in line with a previous, IIHS study that claimed increases in speed limits from 1993 to 2013 resulted in 33,000 additional deaths, despite advances in safety technology in automobiles made during that time. The study found there was a 4% increase in fatalities with every 5-mph increase in the speed limit, even when accounting for external factors, such as the number of young drivers on the road, per capita alcohol consumption, and more.

Another noteworthy finding of that study was that “in 2013 alone, the increases [in speed limits] resulted in 1,900 additional deaths, essentially canceling out the number of lives saved by frontal airbags that year.”

In short, the IIHS argument is that speed limits should have never been increased to exceed 55 mph. Of course, if you follow the logic that lowering speed limits reduces the rate of crash related deaths to its most extreme conclusion, why stop at 55 mph? Why not reduce it to 30 mph? 20 mph? Or just not drive at all?

The struggle, of course, is balancing practicality with safety. Higher speed limits allow for reduced journey times, increased productivity, and less congestion on the roads, but there are safety trade-offs that can’t be ignored.

Until self-driving cars become the norm, perhaps the most important step we can take to keep our roads safe is to better educate our drivers in the first place to reduce dangerous behaviors on our increasingly faster streets.