Motorists who use Interstate 35W in Bloomington have encountered lane, ramp and shoulder closures over the past few weeks as Minnesota Department of Transportation crews make repairs to wooden noise walls on the side of the freeway.
The repair project between 82nd and about 106th streets began last fall and is expected to be completed this month, said Natalie Ries, MnDOT's Metro District Noise and Air Quality Program supervisor.
Drive reader Dick has seen workers taking down the old barriers and installing new wood in their place. He wanted to know why the walls were being replaced since it seems like they "should last a lot longer."
The walls he is referring to were some of the first installed in the metro area when they became part of the landscape in 1978. As things tend to do in Minnesota's harsh climate, the walls have weathered since then. The concrete pillars are still in good shape, but the wooden planks have splintered and holes have appeared, leaving gaps that allow noise to sneak through into nearby neighborhoods and business areas the walls are meant to buffer from sounds, Ries said.
The same thing was true along the segment of Hwy. 52 that runs through West St. Paul, South St. Paul and Inver Grove Heights. MnDOT this spring completed fixes on failing walls and concrete posts and removed vegetation.
Solid barriers block the direct path of sound waves from the highway but don't totally eliminate it. Noise can go over the walls and around them, Ries said. But for those within 500 feet of a highway, "they are effective," she said.
The constant hum of freeway traffic can generate noise levels in the 65 to 70 decibel range. According to the Minnesota Pollution Control Agency, that is akin to the volume of a normal conversation with a person 3 feet away (on the low end) or a vacuum cleaner (on the high end).
With the noise walls, Ries said, "we can see a seven to 10 decibel decline. It's easily noticeable."
