Over the past several years, ODOT has had cabled median barriers installed for pretty much the entire length of Interstate 5 through Oregon. One thing has puzzled me, though, as I’ve driven up and down the interstate. The barriers are usually located along one side or the other of the center median, but sometimes they are right in the middle of the median, too. So, my question is: What sort of design criteria were used to determine which side of the median (or in the center) the barrier was placed?
— Robert J., Ashland
Well, Robert, often the design criteria is related to something that was designed long before the barriers were put in place.
The safety cable barrier system on I-5 has been in the works for at least five years, but picked up steam in the wake of a tragic 2014 crash in Salem in which a pickup crossed the I-5 median and struck an oncoming car, killing both occupants.
There are some rules for placement of the cable barriers, according to Gary Leaming, a spokesman for the Oregon Department of Transportation:
In general, they are placed on the outside curve to catch out-of-control vehicles.
They also are placed roughly 8 feet off paved shoulders to allow for maintenance, such as grooming and mowing.
The other consideration is the location of existing features such as drainage culverts and inlets.
Those culverts are often in the center of the median because that's likely the lowest spot for drainage. Drilling post holes into existing drainage lines would not work well for either function.
Leaming said the cable barrier is in the middle of the median between exits 11 and 14 near Ashland because of the southbound chain-up area, which can create something of a bottleneck for traffic.
He also noted that in the Gold Hill and Rogue River area, the inside shoulder is being widened to 6 feet because that shoulder was so narrow it almost reached the fog line. The widening provides drivers with more room in case something happens while they're moving or if they need to pull over and stop.
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