Written by Adrian Lund, president of the Insurance Institute for Highway Safety. This is one in a series of periodic guest columns by industry thought leaders.
Few things carry more potential risk than a semi-trailer barreling down the highway at 80 mph. The federal government’s plan to require speed limiters on large trucks that would hold their speeds to a set level — probably 68 mph or lower — is a logical step that would improve safety.
Extreme speeds have become commonplace as state legislatures around the country have set higher and higher limits. These higher speeds are more dangerous the heavier the vehicle. Large trucks have longer stopping distances than other vehicles, making it more difficult for them to avoid a crash. When a crash does occur, speed and vehicle weight determine the energy involved and therefore the severity of the collision. Even a lightly loaded 40,000-pound truck has 13 times the energy of a 3,000-pound car traveling the same speed.
Although the danger of high speeds is compounded for large trucks, the trend of continually raising limits has consequences for all road users. Our research at the Insurance Institute for Highway Safety has found that 33,000 deaths between 1993 and 2013 can be attributed to speed limit increases. The annual toll from speed limit increases largely cancels out the number of lives saved every year by frontal air bags.
State legislatures set the maximum speed limit in each state, and since 1995 they have been allowing higher and higher limits. The beginning of that trend followed the unraveling of the national maximum speed limit, a federal law that required states to adopt 55 mph as their maximum speed limit in order to receive their share of highway funds. Concerns over fuel availability had prompted Congress to adopt the measure in 1973, but another benefit was a decrease in crash deaths of 4,000 in the first year alone.
As energy concerns faded, Congress relaxed the restriction in 1987, allowing states to adopt limits of up to 65 mph on rural interstates. A complete repeal came in 1995. Since then, states have been adopting higher and higher limits. Today, 41 states have limits of 70 mph or higher on some roads. That includes six states with 80 mph and one — Texas — where drivers on some roads can travel 85 mph.
Despite the deadly consequences of extreme speeds, the idea of lowering limits for all vehicles hasn’t gained traction in legislatures. Given this reality, we welcome the proposal by the Federal Motor Carrier Administration and the National Highway Traffic Safety Administration to at least put a cap on the speeds of the biggest vehicles.
Some critics of the proposed rule have raised concerns about different vehicles on the same road traveling at different speeds. But most trucks already travel at lower speeds on average than passenger vehicles. That’s in part because many companies voluntarily use speed limiters to improve safety and fuel economy. In addition, seven states have lower maximum speed limits for trucks than for passenger vehicles.
However, a small number of trucks do travel at very high speeds, putting their drivers and the people in vehicles around them at grave risk. We recently studied the effect of raising speed limits from 75 to 80 mph for all vehicles on certain road segments in Utah. We found that the proportion of large trucks exceeding 80 mph rose from 0.1 percent to 2.3 percent.
While still a small number, every truck traveling that fast represents a big risk because it has 50 percent more energy to manage in an emergency situation than if it were traveling 15 mph slower. Speed limiters that physically prevent trucks from traveling that fast are one way to make roads safer for everyone.
Editor’s note: Adrian Lund is president of the Insurance Institute for Highway Safety and the affiliated Highway Loss Data Institute. He joined the Institute in 1981 as a behavioral scientist.