Advertisement

Bridges Span Time--Back to Wood

Share via
NATIONAL GEOGRAPHIC

The Stewartstown Bridge, an unobtrusive, 44-foot span across a small stream on the outskirts of this college town in the Appalachian Mountains, is a bridge between the past and the future.

That is because it was built just a year ago and it is made of wood--northern red oak and southern yellow pine.

If the 3-year-old federal National Timber Bridge Initiative catches hold, wood will replace steel and concrete as the material of choice for hundreds of thousands of minor bridges.

Advertisement

As America’s 19th-Century iron bridges rusted away, they were replaced by 20th-Century concrete and steel. Only one in eight bridges in the country today is built of timber, and most people don’t recognize them as they ride over their asphalt surfaces.

The crumbling condition of the nation’s 577,000 bridges is well-documented. Four out of 10--more than 230,000--are considered functionally obsolete or structurally defective.

Those include bridges only 20 feet or longer, the ones covered by the federal inspection program enacted by Congress in 1967, the year the Silver Bridge between West Virginia and Ohio collapsed and 46 people were killed.

It doesn’t include hundreds of thousands of bridges shorter than 20 feet, which aren’t subject to federal inspection.

Dedicating the Stewartstown Bridge in August, 1990, Sen. Robert C. Byrd (D-W. Va.) father of the Timber Bridge Initiative, said:

“Fortunately, experts in bridge construction have discovered that technologically treated hardwood timbers could be used in the replacement of as much as 80% of our country’s dangerous or obsolete bridges.”

Advertisement

In West Virginia, one of the poorest states, Byrd is pushing for use of underutilized hardwoods such as yellow poplar and red maple. The idea is to use a renewable source of low-grade wood. Softer woods can be used, too, if they respond well to chemicals that make them impermeable.

The treated wood, assembled in laminated sections, can then be tightly compressed with steel rods extending through pre-drilled holes that run the width of the bridge.

The whole process is relatively quick and inexpensive. For each of the 178 demonstration bridges built so far under the initiative, the average cost has been $68,000. The maximum length of a timber bridge is about 120 feet.

Wooden bridges, unlike concrete and steel ones, resist deterioration caused by de-icing chemicals. A good timber bridge, the experts say, will last at least 70 years. Only the road surface wears out periodically.

The bridge initiative’s latest status report uses federal Transportation Department figures to arrive at a shocking conclusion:

“Within the next four years the lost productivity resulting from bad roads and bridges will cause a 3.3% decline in the gross national product, an 8% increase in the consumer price index and a 2.2% reduction in employment.”

Advertisement

The author of the report, John Pasquantino, legislative liaison for the initiative’s northeastern area, explained:

“Bridges represent more than getting across streams. They connect rural markets with suburban and urban areas. They are critical to the infrastructure to get products and services to and from rural areas.”

Since Byrd announced the bridge initiative in 1989, nearly $6 million in federal funds has been spent on it, matched by $10.4 million from state and local governments. Another $7.8 million has gone into timber bridges in national forests.

Advertisement