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NYC Tranit Authority Signal Improvemnts

1. Upgrade the signal system quickly and relatively inexpensively to:

a. Eliminate failure pone electromechanical relays.

b. Eliminate failure prone rubber or fabric insulation.

c. Provide a basis for rapid and inexpensive transition to Computer Based Train Control.

d. Reduce operational costs.

2. Upgrade the signal system by talking the following steps:

a. Cut the signal cables near to the entrance to the tower.  At each side of the cut, install a fiber optic multiplexor.  A “mux.”  Note: A mux is a device that allows one pair of wires or fiber to carry many signals.  The system continues to operate as before, but the mux isolates the tower from the track.  And, on the tower side, it can provide a second fiber output that I will discuss later.

b. Once the mux is in place, the mux and fiber can gradually be moved closer to the track circuits, eliminating much of the cloth or rubber insulated copper wire that is easily damaged merely by touching it.

c. One by one, the track circuits can be disconnected from the coper wires and connected to the fiber.  Or a different type of train sensor could be installed and connected to the fiber.  Either way, a delicate cable, prone to failure, is removed from the system.

d. The second output of the mux could be routed to a computer switching system that would replace the functions of the electromechanical relays in the tower.  When all of the cables to the tower are connected to the computer system, the new, electronic, tower can be thoroughly tested, and the old, electromechanical tower can be taken out of service.  A significant point of failure would thus be removed from the system.

e. At this point, the system operates as before, but at lower maintenance cost and with far fewer failures.  System reliability would be enhanced, although it would not provide a completely new system.  But it would reduce signal failures to almost zero.

f. The next step would be to upgrade the software to support computer based train control (CBTC).  Note that this should only necessitate a software change.

g. With CBTC operational, new track side hardware could be installed to more precisely identify train location and increase the track capacity.

h. CBTC would thus be installed in easy, manageable steps without having to cut over an entire line at once.  This has been a successful model for the telephone industry for decades.  There is no reason that it would not work for the Transit Authority.


There has been much discussion about replacing the entire signal system to allow a few more trains per hour to operate over a track but little consideration of reducing failures.  The current model is to cut over an entire line at once, after a new, parallel system is installed.  I suggest that the model proposed above provides a quick solution to the largest problem, reliability while allowing more rapid installation of CBTC and at a lower cost