Transportation Matters in Iowa | Blog

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Cable median barrier saves lives and creates challenges for maintenance crews


First day test I35 (7)In an effort to reduce the number of fatalities from crashes where vehicles cross the interstate median and collide with vehicles on the opposite side, the Iowa Department of Transportation began installing tensioned cable median barrier in 2007. Each year, as more barriers have been added, the number of cross median fatalities has been reduced, from 16 in 2010 to six in 2014. The data shows the barriers are a good safety innovation, but Iowa DOT maintenance folks were left with the dilemma of safely mowing around each of the posts that support the cable barrier.

Since the Iowa DOT policy on mowing for “sight and safety” took effect a few years ago, the number of hours spent mowing has decreased significantly. Under this policy the need to mow the entire stretch from the shoulder to the fence row has been reduced to mowing a 10- to 15-foot swath in areas where not mowing would create a safety hazard or where the sight distance is reduced if the area is not mowed.  

Because the barrier rail borders the inside lanes of the interstate, the area around it must be mowed to allow our maintenance crews to see any damaged posts and repair the barrier as necessary. Traditional mowing methods would require four employees in four separate vehicles: one person operating the mower, two people in crash cushion vehicles and a fourth vehicle with warning signs. The train of slow-moving vehicles would need to drive on the inside lane, putting both our employees and travelers at risk.

First day test I35 (4)Never ones to shy away from a challenge, Iowa DOT maintenance crews studied several ways to increase safety and traveler convenience while getting the job done of mowing around the cable barriers. “We needed a better way to mow around this cable median barrier,” said Ken Morrow of the Office of Maintenance. “We did our research and found a solution in a mower head that can be mounted to one of our existing tractors and shared among the districts.”

In late July the new mowing head was delivered and crews in central Iowa got to work on Interstate 35. Since the head can be used off either side of the tractor, it allows for the tractor to be driven in the median, where it doesn’t hamper traffic or require additional vehicles to operate safely.

Morrow said, “We started on I-35 and then moved to I-80 east of Des Moines, I-380 from Cedar Rapids to Iowa City, and then I-80 west of Des Moines. In just a few months, we’ve been able to mow every area on the interstate that currently has cable median barrier. As we continue to add more miles of cable, we may need to invest in a second mower head, but for now, the districts have set up a schedule to share the mower and get all the work done with one piece of equipment.”

Benefits of mower

The cost of the new mower head was $48,000, about the same cost as typical damage cause by one crash cushion being hit. This mower technology may seem like a small step forward, but the safety benefits to DOT staff and the traveling public are significant while not restricting traffic flow.  

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Iowa highway in the evening