As the prototype for the "modern" heavy rail rapid transit system, Philadelphia's PATCO (Port Authority Transit Corporation) Hi-Speed Line was naturally designed with state of the art signaling. However as a prototype it had a few features rooted firmly in the past. For example it had cab signals without wayside block signals, but it used PRR style 100hz pulse codes as opposed to the audio-frequency track circuits that would appear on the DC Metro and BART. One of PATCO's most visible links to traditional railroad operation was its signaling control where the full-line CTC was placed not in a command center or dispatch office, but a "tower" built and named for the PRR interlocking tower that had occupied the same location for the previous 40+ years.
As built by the Pennsylvania Railroad, CENTER tower sat at the 3-way junction where trains from the Federal Street Terminal would fan out en-route to various points along the South Jersey shore from Long Beach Island to Cape May. Older than the wave of towers that accompanied with 1934 PRSL merger, CENTER featured a 66-lever EP machine and despite the drop in passenger traffic throughout the 1950's, still saw plenty of action from freight trains and lite engine moves to the PRSL's primary service facility at the old Federal Street complex.
This would change in 1966 when construction on the PATCO Hi-Speed line commenced. The project would replace the PRSL's Broadway station and the associated trackwork controlled by the old CENTER. The resulting real estate was repurposed for Interstate 676 and all traces of the old CENTER tower was erased, however the spirit of CENTER would live on in the new PATCO Hi Speed Line.
When completed, the PATCO Speedline consisted of the existing 1936 vintage Delaware River Joint Commission "Bridge Line" between Camden and downtown Philadelphia along with a brand new grade separated rapid transit line to the New Jersey suburb of Lindenwold. The new and old parts of the line joined just east of the old PRSL Broadway station in a space that would have been physically within the territory of CENTER tower. As PATCO tried to re-use as much existing infrastructure as possible it was decided to build the CTC office at this junction point as it could directly interface with the existing signaling and telecom links from the Bridge Line and not have to somehow forward those signals all the way to Lindenwold. Because PATCO's design team were generally rail enthusiasts, they named their CTC office after the old PRR CENTER tower.
Technically the structure did count as a traditional tower as the operating floor was located above a typical PATCO substation. In addition to the unit lever CTC machine, CENTER also supported traction power direction and remote customer service via "call for aid" telephones and CCTV. CENTER would serve PATCO well for over 50 years, however as the systems were upgraded over the decades, the rationale for its existence, supporting direct wire control cabling, would no longer apply. Instead CENTER would be physically isolated from the main PATCO offices and shoppes in Lindenwold and also located in what had become one of the most dangerous cities in America. With the building starting to age and the work-site unpopular with employees, PATCO eventually found the money to build a brand new state of the art control facility at Lindenwold.
Although the original CENTER tower will be retained as a backup facility, much of the spirit of classic railroading that CENTER represented is likely to be lost.
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