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Re: MTA removes or increases more speed limits

Posted by Stephen Bauman on Sun Mar 17 07:54:31 2019, in response to Re: MTA removes or increases more speed limits, posted by SUBWAYMAN on Sun Mar 17 00:35:36 2019.

The railroad industry's signal technology and implementation was developed about 40 years before Shannon developed the theoretical basis for digital circuit design. The rest of the world embraced Shannon's breakthrough and moved on. The railroad industry did not.

One result has been that railroad signaling implementations are expensive museum pieces. The rest of the world was able to make use of ever less expensive components and implementations.

The rest of the world also diverged from the railroad industry on the subject of how to build reliable circuits. The railroad industry's basis for circuit reliability is ever more reliable (and expensive) relays which they call vital relays. The rest of the world achieved reliability through redundancy. This basis for this approach was presented in a 1956 paper by Moore and Shannon entitled "Reliable Circuits Using Less Reliable Relays."

The next revolution that the railroad industry missed was the substitution of Programmable Logic Controllers (PLC's) for hard wired digital circuits after 1975. A PLC is a computer and program that simulates any logical circuit. The PLC's program accepts any logic circuit as data. PLC's are most responsible for the factory floor automation that has taken place since 1975. The PLC's have become commodities and are designed to function in harsh industrial environments.

There are approximately 15K individual signal blocks. If each cost $500K to implement and install with a PLC, then the total replacement cost would be $7.5B instead of CBTC's $40B+.


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