Several serious accidents this year on a stretch of US 231 near Troy have raised the question of whether medians make highways safer. An Alabama Department of Transportation (ALDOT) spokesperson and Troy Police Chief Randall Barr disagreed about medians in a Troy Messenger story. Traffic safety research addresses questions like this, and suggests that median barriers, if not medians themselves, provide considerable safety.
ADOT’s Tony Harris was quoted in the Messenger saying, “Nearly every crash is caused by driver error or driver behavior. There is only so much we can do from an engineering standpoint to compensate for that.” The contribution of driver error to almost every accident is indisputable, and is why self-driving cars offer so much promise. But the design of roads also matters.
According to the Federal Highway Administration, head-on collisions are three times more severe than other accidents, and higher speeds make these collisions worse. Rural two-lane roads and highways tend to produce high speed, head-on collisions, making rural driving more deadly than city driving. Although about as many deaths occur on rural and urban roads, much more driving occurs in urban areas. And even though heavy traffic and frequent stops and starts might make us think city driving is more dangerous, rural driving has head-on collisions, drowsiness from longer trips, and longer emergency response times.
Road designs clearly affect fatalities. Freeways are the safest highways, as medians and limited entrances and exits make travel safe despite high speeds. Rural highways like US 231 (arterial roads for transportation geeks) have the highest fatality rate, about three times greater than rural interstates or urban arterial roads.
Developed in the 1950s, concrete median “Jersey” barriers on urban freeways illustrate how roads can be made safer. I remember these barriers being installed around Detroit in the 1970s. The angled base helps direct vehicles back onto their side of the highway. Although hitting Jersey barriers damages cars, keeping vehicles from crossing into oncoming traffic saves lives.
Jersey barriers were among the safety measures which reduced traffic deaths from 50,000 annually in the 1960s to less than 35,000 by 2009, despite a tripling of miles driven nationally. Fatalities per million miles driven have fallen by eighty percent over the last fifty years. To appreciate the significance of this, at 1960s fatality rates, today’s traffic volumes would result in over 120,000 additional highway deaths per year.
Determining the exact contribution of Jersey barriers to the reduction in traffic deaths, as opposed to seat belts, air bags, anti-lock brakes, and reduced tolerance of drinking and driving, is extremely difficult. Studies examining the effect of installing median barriers in North Carolina and South Carolina, though, provide reliable evidence. Cross-over fatalities fell by 90 percent, and 99 percent of vehicles veering into the median were prevented from crossing into the other lanes.
North and South Carolina installed median cables, which at $55,000 per mile are far cheaper than Jersey barriers’ cost of $1 million per mile. Although Jersey barriers are sturdier, the combination of high effectiveness and low cost make median cables a better option for rural highways.
Narrow grass medians may no longer be effective due to today’s higher traffic volume. The Federal Highway Authority now recommends barriers for medians less than 70 feet wide. At lower traffic volumes, grass medians provided enough stopping power for the occasional vehicle straying into the median. And the likelihood of a car which crossed the median striking a vehicle traveling the opposite direction was low. Today’s traffic volumes require barriers.
Avoiding driver error is the best way to prevent accidents, but highways can be made safer. Technology creates new options, but also complicates decisions about long term safety investments. Cable median barriers may make sense today, but lane departure warnings and self-driving cars might render barriers unnecessary. Should we invest in barriers today, or wait for better technology? Sometimes I’m glad just to be offering commentary instead of making such decisions!
Daniel Sutter is the Charles G. Koch Professor of Economics with the Manuel H. Johnson Center for Political Economy at Troy University and host of Econversations on TrojanVision. The opinions expressed in this column are the author’s and do not necessarily reflect the views of Troy University.