The Grand Coulee Bridge, or Columbia River Bridge at Grand Coulee Dam, is a through-cantilever steel truss bridge built in 1934–35. It carries State Route 155 across the Columbia River immediately below Grand Coulee Dam, near the city of Grand Coulee, Washington. It was added to the National Register of Historic Places in 1982. The bridge was built to transport heavy equipment across the Columbia River during the construction of the dam, and thereafter as a permanent highway bridge. As such, it was designed to carry a heavier load than was typical. The bridge is supported by two concrete piers, about 150 ft high. During construction, one of the piers began to tilt, probably due to fine glacial material under the gravel. Additional supports were added as a temporary measure. It employed between 1,000 and 1,200 men. The piers were later taken down to bedrock using pneumatic caissons.