Real Bridges to the 21st Century

The Interstate 10 bridge near New Mexico State University in Las Cruces may not be very exciting to look at. But the Federal Highway Administration, the National Science Foundation and state highway departments are hoping that a "smart bridge" system currently being tested there may one day revolutionize bridge maintenance on the interstate highway system.

Beneath the Las Cruces bridge are dozens of fiber-optic cable sensors that--once the experiment is fully underway--will remotely transmit their data to bridge officials. The idea is that when a weakened bridge is hooked up to the system, it will be able to communicate directly with bridge engineers, who will then be able to check for damage and possibly prevent a major bridge failure.

Before the cables were placed, Naval Research Laboratory scientists used laser beams to etch them with internal gauges. Engineers then arranged for light beams to zoom down the cable at regular intervals. The degree of light-beam bending through the gauges indicates how much stress the bridge is experiencing. The gauges can also sense how much traffic is passing overhead.

Rola Idriss, a New Mexico State University civil engineer who is monitoring the I-10 experiment, acknowledges both technical and economic challenges. With the sensors costing between $50 and $100 each, highway officials who aren't involved in the experiment suggest that the system would be most appropriate for perhaps 10 percent of bridges. Likely candidates would include bridges already suspected of being structurally deficient, urban bridges that carry economically vital traffic flows, and newer bridge designs with short track records.

Supporters, however, argue that the new system would free bridge inspectors from routine duties and enable them to focus on more pressing work. In addition, highway departments would be able to use the sensors' data to repair bridges more cost-effectively.

California officials are seeking to install experimental fiber-optic gauges in critical seismic zones, and the heavily traveled Woodrow Wilson Bridge over the Potomac River near Washington is also being touted as an early test site.