(m4bridge-trestle-tx-sansaba-2009-1028.1257) San Saba River Trestle Bridge
A trestle bridge is a bridge composed of a number of short spans supported by closely spaced frames. A trestle differs from a viaduct in that viaducts have towers that support much longer spans and typically have a higher elevation.
Timber trestles bridges were extensively used in the 1800s, with these bridges making up about 2 percent of the total length of the average railroad. In the 2000s, steel and sometimes concrete trestles are commonly used to bridge particularly deep valleys, while timber trestles remain common in most areas.
Many timber trestles were built in the 1800s and early 1900s with the expectation that they would be temporary. Timber trestles were built to get the railroad to its destination and once the railroad was running, it was used to transport the material to replace trestles with more permanent works, transporting and dumping fill around some trestles and transporting stone or steel to replace others with more permanent bridges.
Then, in the later half of the 1900s, many earthmoving tools made it easier and cheaper to construct a high fill directly instead of construction a trestle from which to dump the fill. Still, despite the advances in technology, timber trestles remained common in some applications, most notably for bridges crossing flood-ways.
Notably, nearly all trestle bridges were built to carry heavy railroad lines.
Lucin Cutof
Probably, the most notable trestle bridge was along the Lucin Cutoff which is a 102 mile railroad line in Utah, that runs from Ogden to its namesake at Lucin. The most prominent feature of the cutoff was a twelve mile long railroad trestle bridge crossing the Great Salt lake and was used from 1904 until the late 1950s, when it was replaced with an earthen causeway.
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