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Tim Harlow,

The Drive: Why highway cable barriers aren't always centered

  • Article by: Tim Harlow
  • Star Tribune
  • March 17, 2014 - 10:34 AM

Kris from Stillwater noticed something curious about the cable barriers strung along the medians on many of our highways and freeways.

Sometimes they are in the middle of the median, and other times they are right up against the traffic lanes and jump from one side of the highway to the other.

Why the difference?

Cable barriers — made of three or four steel cables strung on posts — are designed to keep out-of-control vehicles from crossing the highway and crashing into oncoming traffic.

They work like this: When a car hits the barrier, the posts break and the cables flex, absorbing much of a crash’s kinetic energy. This redirects the vehicle along the median, preventing a cross-median crash. Minnesota Department of Transportation (MnDOT) officials say the barriers can reduce fatal crashes by 90 percent.

They first appeared on Interstate 94 between Rogers and Maple Grove in 2004. Since then, they have been installed on hundreds of miles of grassy medians in highly traveled areas where such crashes have or could potentially occur. More recently, the barriers were installed along Interstate 94 through Woodbury.

While many barriers run right down the middle of the median, that isn’t always the best place.

The middle is often a low spot, so there’s a “distinct possibility” of an errant vehicle vaulting over the cables. The soils are often poor, said Kent Barnard of MnDOT.

If one direction of the freeway is higher than the other, that side of the median gets the cable. Engineers also review which side of the road has had more drivers zooming into the median. They’ll place the cable on the opposite side to give the veering drivers more room to recover on their own, Barnard said.

Barnard learned another tip firsthand a few weeks ago, during one of our many snowstorms. He was driving a snowplow on I-35W south of Forest Lake, plowing snow off the left shoulder and into the cable median. He was told to push the snow away from the cable barrier because the barriers lose their effectiveness when they are snow-covered.

While we’re talking about medians and shoulders, Barnard said that anyone making an emergency stop should use the right shoulder if possible, because it’s wider and safer than those on the left side.

Metro Mobility

Last month, I wrote about the Metropolitan Council’s proposal to create a downtown fare zone for Metro Mobility riders. The council is expected to vote on the issue March 26. Helen from Brooklyn Center noticed that Metro Mobility vehicles don’t have license plates and wondered why.

Metro Mobility is a service of the Met Council that provides transportation for people who are unable to use regular route buses or trains. The vehicles are owned by the council and leased to private providers who use them to provide a public service, said Andrew Krueger, Metro Mobility senior manager.

State statute 168.012 says that vehicles owned and used solely in the transaction of official business by the federal government, the state or any political subdivision are exempt from taxes, fees and plate display. Krueger said that the Met Council qualifies as a “political subdivision” and that since the vehicles are owned by it and used solely in the transaction of official business, “we are exempt.”

Follow news about traffic and commuting at The Drive on startribune.com. Got traffic or transportation questions, or story ideas? E-mail drive@startribune.com, tweet @stribdrive or call Tim Harlow at 612-673-7768.

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