The price of safety: Study to analyze when, where to use cable median barriers on Iowa highways

The cable barriers along Interstate 380 blend into the background, until a vehicle veers off the road.

Tensioned to about 4,500 to 5,000 pounds of pressure, the braided steel cable absorbs the impact of a collision. The posts, anchored in the ground every 20 feet, are designed to break away to let the cable flex and stop a vehicle from crossing the median.

As traffic increases on Interstate 380, the number of hits on these cables keep local maintenance workers busy.

'We've had quite a few hits lately. We had three accidents on 380 this week,' said Johnny Shanahan, supervisor of the Iowa Department of Transportation's Cedar Rapids maintenance office. 'One car was stuck in it to where the tow truck couldn't get it out. We had to release the tension to get the vehicle out.'

There have been 464 hits so far this year on cable median barriers in the Iowa DOT's District 6 region, which includes I-380 and I-80 in Cedar Rapids and Iowa City, according to figures from the agency.

But the minor crashes and damage are outweighed by the benefits, officials say.

State officials believe the rollout of high-tension cable median barriers along Iowa's interstates and highways is connected to a sharp decline in one of the most serious kinds of motor vehicle crashes — head-on collisions — since 2011.

The notion contrasts public fears the cables create more dangers by slingshotting cars back into traffic like a rubber band, or slicing through vehicles, said Chris Poole, a safety programs engineer at the Iowa DOT headquarters in Ames.

'These barriers are designed to be flexible and absorb the impact of the crash,' Poole said. 'It is drastically reducing the incidence of cross-median fatalities and injuries on our highways.'

The Iowa DOT has hired Iowa State University's InTrans to study the effectiveness of the safety tool, and whether it is worthy of the cost of adding more lane miles.

The Federal Highway Administration identifies cable median barriers as an effective safety measure to consider and recommends states review median crossover crash histories to identify locations for use.

$120,000 per mile

Iowa began limited use of the barriers in 2003. By 2007, less than 6 miles of cable medians existed on Iowa's interstates, and less than 42 miles by the end of 2010, according to Iowa DOT data.

With a spike in head-on crashes, available federal safety dollars and the urging of then-Gov. Chet Culver, the Iowa DOT rapidly deployed the technology in 2011, adding 175-lane miles in that year alone.

Since then, a five-year strategic highway safety plan has called for an additional 20 miles per year. By the end of this year, 330 miles of median will be installed around the state.

But that plan ends in 2016, prompting the ISU study to determine whether the practice should continue.

On the surface, the answer appears obvious.

According to Iowa DOT data, between 2004 and 2010, Iowa averaged 15 cross-median fatalities per year and 27.6 injuries including five major injuries. Since then, cross-median fatalities declined to 6.5 per year and 14.5 injuries including three major injuries.

The barriers cost about $60,000 per mile, but that increases to $120,000 per mile with necessary grading and other related work, Poole said. That's actually cheaper than steel guardrails or concrete barriers, which are more common in spatially constrained urban areas.

There's also the cost of repairs.

The Iowa DOT District 6 office has a one-year, $645,500 on-call contract for guardrail repairs with Dave Gryp Construction of Victor. So far this year, the company has been paid $552,853, according to data provided by Steven Staebler, an Iowa DOT construction tech supervisor in Cedar Rapids.

Peter Savolainen, an associate professor of civil, construction and environmental engineering at Iowa State, is conducting the two-year, $150,000 study, which began in July.

As part of the study, he will examine data about crash locations, injuries and fatalities before and after crash barriers were installed. The data will help evaluate the cost-effectiveness of the barriers as well as consider candidates for future locations, he said.

Savolainen concluded a similar study for the Michigan Department of Transportation — which has about the same amount of cable miles as Iowa — earlier this year.

That study concurred with the preliminary Iowa data that the cables reduce the most severe fatal crashes. However, it showed a significant increase in minor crashes, he said.

Minor crashes increased 155 percent and property damage cases climbed from 404 per year to 1,100, he said. In contrast, the number of fatalities and serious injuries from cross-median collisions were cut in half.

Part of the equation is looking at the cost of different types of collisions. A property-damage collision costs on average $8,900, while the cost of a fatal crash is $4.5 million when looked at over a lifetime, Savolainen said, citing information from the National Safety Council.

'That is the price we are paying to eliminate more severe crashes,' he said.

Poole said he expects Iowa to continue expanding the use of cable barriers, although he added he can't be sure until the strategic plan is developed. More installations are planned this year for Western and Northern Iowa.

'These have eliminated the cross-median crash problem at those areas we've installed the barriers,' Poole said.