Transportation routes often stay nearly the same, even when the form of transportation changes. As a result, the Erie Canal, the main line of what used to be the New York Central Railroad, I-90, and state route 5 (the predecessor to I-90) run parallel through a chunk of upstate New York. The picture above was taken from the train.
The structure above is not a truss bridge, which is sort of obvious if you closely (click on it to expand it) and see that there’s no connection on either end of the upper level “roadway” to grade. It’s a movable dam for the Erie Canal and I find it to be an interesting piece of technology and history.
The original Erie Canal (the famous one) was a hand-dug channel for its full length, with a series of locks to address the differences in elevation along the route and between the Hudson River (sea level) and Lake Erie (some 570 feet higher). The conversion of the canal into the centerpiece of the New York State Barge Canal system shortly after 1900 was accomplished, in part, by canalizing a portion of the Mohawk River. In other words, rather than dig a much bigger channel, the engineers altering the canal decided to create a stable flow of water by putting dams in the river. The picture above is Lock 11 and its moveable dam, Dam 7.
There’s a terminology question here: if the dam is designed to allow water to flow over its top on a regular basis – as seen here – its functioning more like a weir. I guess that it’s called a dam because “intermittent weir” sounds even stronger than “moveable dam.” In any case, the truss structure is to provide bracing to the water-mounted portions of the dam, which can raise or lower depending on water conditions.
Also, it’s very cool to film as the train goes by:
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