Why Over Running Third Rail?

Discussion of the past and present operations of the Long Island Rail Road.

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Patrick A.
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Why Over Running Third Rail?

Post by Patrick A. »

Greetings All,
I was wondering why the LIRR chose over running third rail for their electrification of their lines? Was the under running Wilgus design for the NY Central patented during the early stages of the electrification project, or was there influence by the PRR?

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Post by LongIslandTool »

Both the over-riding and under-riding third rails were tested on the Hempstead Plain by the PRR in preparation for electrification from Brooklyn to Rockaway Park in 1906.

There was a memo written at the time that said the over-riding was more reliable in high snow.

We know now that it is less reliable in freezing rain.
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Post by RearOfSignal »

The under-running design was patented by the New York Central; other railroads and the NYC Subway at the time had already started using the over-running design. The PRR first electrified it's rail lines in NY with third rail, it later realized that it could do better with overhead trolley wires which required fewer substations is reflected in its later electrification projects.
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Post by Noel Weaver »

Under running was and still is used on the Market Frankford Line in
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Otto Vondrak
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Post by Otto Vondrak »

I thought it was something having to do with August Belmont and his Interboro Rapid Transit that was being built and electrified at the same time. Wasn't there short lived inter-line services between LIRR and the IRT? Weren't the MP-41's designed to run in the tight confines of the IRT tunnels if need be?

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Post by RussNelson »

When I was a kid, growing up on Long Island, I thought that over-running was the standard. I only noticed earlier this spring that other NYC trains used under-running.

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Post by LongIslandTool »

Otto did hit the nail on the head.

The MP-41's were indeed built for joint service with the IRT, and a connection was built in the Atlantic Avenue station for the joint service. This probably had a large say in the LIRR's choice of over-riding third rails.

And for about ten years in the early part of last century there was a joint service where Rapid Transit trains originated Downtown and traveled out to Rockaway Park, hooking up with the Atlantic Branch at Chestnut Street. They were equipped with an adaptable shoe mechanism that would convert the shoe distance between the running rail and the third rail.

The LIRR has more distance between the running and third rail than the subway.

That mechanism is pictured in Seyfried's Volume 5.
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why overruning third rail

Post by keyboardkat »

The Sprague-Wilgus underruning third rail had to be of lighter structure with lower conductivity.

With regard to the joint LIRR-BRT service over the Williamsburg Bridge to the Rockaways, in those days the BRT (later BMT) used a third rail that was higher and closer to the running rails than the IRT or LIRR. The paddle-type shoe used by NYCTA subway cars was able to service both.
I remember seeing this on the old Broadway Brooklyn line in the 1950s and on the old Culver Shuttle as late as the 1970s. So the MU cars used in the joint service had the Boyd movable third rail shoe mounting which was actuated by a stationary cam mounted on the crosstie in line with the third rail at the transition point.

Today the LIRR and all the subway lines have the same third-rail gauge.
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