1920

Kinsol Trestle Bridge

It’s a classic shot in the old western movies—the wooden trestle bridge used to carry train tracks over a valley. The reason it is so classic is because these bridges were extremely common in the nineteenth century, especially for railroads, especially in the western United States. If you were building a railroad and it needed to cross a valley, chances are the engineers used a trestle bridge to do it. It was the easy, accessible, inexpensive thing to do.

The Kinsol Trestle in British Columbia, completed in 1920, is an example of a large wooden trestle bridge that survives today. It is 617 feet long (188 meters) and 144 feet (44 meters) high at the deepest part of the valley. It also has a graceful curve built into the structure. It is made of wooden timbers and bolts, with concrete footings to separate the timbers from ground contact.

The basic engineering idea behind a trestle bridge is pretty simple. The railroad track is sitting on top of a series of A-shaped frames. The outer two legs of the A shape provide side-to-side stability as well as the verticality. There may be one or more vertical center posts as well between those outer legs. Then a significant amount of horizontal and diagonal cross bracing helps to keep this structure rigid.

It is also possible to make a trestle bridge out of iron or steel, and there are many modern examples. The Tulip Trestle in Southern Indiana is a 2,307-foot-long (703 meters) bridge made of steel lattice beams, and is the longest trestle bridge in the United States. Another place you can see a trestle type of design today is in classic wooden roller coasters at amusement parks and in long wooden piers at the beach.

SEE ALSO Truss Bridge (1823), Diesel Locomotive (1897), Under Friction Roller Coaster (1919).

Train of the Tanana Valley Railroad, Alaska, USA, crossing a trestle bridge at the head of Fox Gulch.