A Straight Line

I talked yesterday about elegant designs versus kludges; here’s an example of what I consider to be an elegant design from the same era as the elevated trains’ third tracking. The Detroit Publishing Company’s title for the 1905 photo above is “Where the subway is an elevated, New York City” and that’s spot on. This is not an elevated line, it’s the original IRT subway, crossing 125th Street on a viaduct over Broadway (now the 1 train). The structure of the viaduct is noticeably heavier than that of the els, which is a reflection of both the heavier weight of the IRT trains and the fact that the IRT was being built to a higher standard.

This viaduct is the only place in the original IRT system (before the Dual Contracts expansion) where the tracks came up above ground, and it’s quite short. The 116th Street station (adjacent to Columbia University) is the usual 20 feet or so below grade, then the 125th Street Station is up on top of the viaduct, and then the 137th Street station (near City College) is back 20 feet or so underground again. The logic of this is quite simple: grade elevation dives down in a valley at this location, and the subway simply continues in almost a straight line, coming up out of the ground as grade falls below it and then going back underground as grade comes back up. The project of leveling Manhattan’s hills and valleys was most heavily focussed below 59th Street (the southern edge of Central Park) and pretty much non-existent above 110th Street (the northern edge of the park). Here’s the area on the Viele Map:

That’s the Hudson at the top (north is to the right) and East River at the bottom. I included the East River in the cropping to show the messy arrangements at Hell Gate. The north end of Central Park is on the left (the area without streets) and those hills are still there; the hills and swamp to the east of the park and the hills to the west of the park have been evened out quite a bit. The big stream that starts around 120th Street and Tenth (now Amsterdam) Avenue, touches the north end of the park and joins the East River near 108th Street is long gone as a recognizable feature. It lives on, buried in culverts and wet cellars, but it’s not on modern maps. A long stretch of that stream runs on a southeast-northwest diagonal, and that line extends as a valley all the way to the Hudson. The big plateau just to the south is Morningside Heights (where Columbia is); the plateau to the north is Hamilton Heights (where City College is). There’s a diagonal street that follows the centerline of the valley labelled as “Manhattan Street”. In 1920, this became the 125th Street west of Convent Avenue. The streets in this area generally do not follow the original grid layout because of the hills.

So where the viaduct crosses 125th Street, it’s not a right-angle intersection. The angle between 125th Street and Broadway is about 60 degrees, meaning that the three steel two-hinged arches that carry the viaduct and station are skewed. The center arch is north of the east arch, and the west arch is north of the center arch. It’s a really nice structure and one of a kind, since the other elevated portions of the subway system use much more standard viaduct construction. I guess William Barclay Parsons, the chief design engineer for the IRT, felt the need to stretch a bit here.

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  1. Pingback: A Straight Line — Old Structures Engineering – The Bridgehunter's Chronicles

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