If all the highway noise wall barriers erected in the U.S. since 1970 were placed end-to-end, they would stretch from San Francisco to Chicago. That’s an estimate from the U.S. Department of Transportation (U.S. DOT), which also calculates the construction of those noise walls cost about $1.9 billion.
Forty-four states have now built highway traffic noise barriers, and state DOTs spend an average of $126 million in highway program funds annually for noise abatement. The U.S. DOT reports that the lowest cost noise barrier material is earth berms, which average about $51 per square meter. Overall costs for wood barriers average about $155, concrete is $198 and brick is $214.
The competition for highway noise wall materials is becoming more intense as steel, concrete and wood increase their research and promotion programs to reach this specialized market. More noise walls are built of concrete than any other material, but timber walls are experiencing an increase in market share.
Laminated in Minnesota
In Minnesota, glued laminated wood panels were selected for a major noise wall project on Highway 169 near Minneapolis.
Vertical-glued laminated timber panels, which vary in height from 6 to 18 ft, are connected to laminated timber posts on Highway 169 between Bloomington and Eden Prairie, Minn. The lamenated panels range in thickness from 1 7/8 to 2 11/16 in. The timber panels were supplied by Sentinel Structures Inc., Peshtigo, Wis., and installed by Shafer Contracting Co., Shafer, Minn.
Minnesota Transportation Engineer Tom Ravn said the glulam wall system has an attractive appearance, long-term durability and competitive costs. The panels are preservatively pressure treated and have a life expectancy of over 40 years.
"The laminated wood panels have a cost and aesthetic advantage over other materials," said Ravn.
Minnesota Transportation Structural Engineer Jim Hill added that the in-place cost of the laminated timber walls is generally about 20% lower than concrete or steel panels. Wood also avoids the vibration and noise problems experienced when steel wall panels work loose in high winds.
And, unlike solid wood plank panels, which sometimes dry out and open up small separations at the tongue and groove (T&G) joints, laminated panels are manufactured with three-ply, kiln-dried lumber without T&G joint openings, according to Minnesota officials.
Laminated wood noise wall barriers also were selected for a 1 1/2-mile section of Highway 100 in the St. Louis Park area of Minneapolis-St. Paul.
General contractor Butch Trebesch of Ames Construction said there were two types of panelized installations on the Highway 100 project. Part of the construction called for pressure-treated, 30-ft glulam timber sections buried in an earth berm about 10 ft, resulting in a wall 20 ft high.
On other portions of the project the timber wall was fastened to concrete retaining walls. The pre-assembled panels were 8 ft wide and 2 11/16 in. thick. There are 2- x 6-in. battens over every vertical joint 8 ft apart, and the panels are capped with a 2- x 8-in. top rail.
Before construction began, the Minnesota DOT held a number of community meetings to get comments and suggestions from property owners on materials and construction techniques for the noise walls.
Timber¾ for the second timeThe durability of laminated noise wall barrier panels was demonstrated in the Chicago area where lanes were added to expand the toll collection facilities on three miles of I-355 (North-South Tollway).
The glulam timber wall sections, originally placed on the tollway in 1989, were found to be in good shape. They were moved and reused in the new configuration.
Engineer John Wagner of the Illinois Toll Highway Authority said there were two types of barriers in the North-South Tollway¾ timber post and panel and timber sections buried in an earth berm. The timber panels varied in height from 15 to 20 ft.Wagner said it’s easier to move and re-erect timber noise walls than concrete walls. The timber walls also were supplied by Sentinel Structures.
Wood shop?
The target for noise reduction with walls in most states is at least 10 decibels.
Studies by the Southern Pine Council and the American Institute of Timber Construction indicated that wood panels can compete for the noise wall market because of their competitive cost and durability against road salt damage. DOT specialists also report that the flexibility of wood systems permits contractors to make slight adjustments to wall and poles in difficult terrain to ensure a snug fit.
There’s also a claim that timber walls can be repaired faster and more economically than concrete or brick if damaged by vehicle impact.
Timber noise walls are lighter in weight than concrete sections, a plus factor when they are attached to bridges.
