muni_generic.jpgThe San Francisco Municipal Railway could become a bit more reliable in coming months as work to replace a critical element of the light-rail system moves forward, San Francisco Municipal Transportation Agency Transit Director John Haley said today.

Work began this spring to replace the cable loop, the automated signal cables that sit between the rails. The exposed cable is vulnerable to damage, which can halt all underground service.

In June, service was knocked out between Church and Embarcadero stations for the entire morning commute after a light-rail vehicle’s sander hose–which spreads sand during emergency braking–damaged signal cable at the Duboce Street junction, spokesman Paul Rose said.

The cable loop sends and receives data from Muni’s main train computer and allows trains to operate in automatic mode in the subway. Delays are caused when the cable is damaged and trains are forced to operate in manual mode, Haley said in a presentation at the SFMTA Board meeting this afternoon.

As the cable has been damaged over the past decade since it has been in operation–by antennas falling off trains and making contact with the wire or by loose hoses on the light-rail vehicles that cut the cable–it has been repaired incrementally with splices.

Although the cable could have a life expectancy of more than 50 years, Muni’s 15-year-old loop cable needs to be replaced, Haley said, because these splices weaken the cable’s signal strength slightly and reduce the reliability of the system.

“It’s stable and reliable, but it’s not quite as reliable as it could be,” Haley said.

Because the splices are the weak spot in any cable, replacing the cable improves reliability, Haley said.

The first phase of the repairs, consisting mostly of preparation work, began in the spring and is expected to be completed by the end of the month, Haley said.

In the next week, the cable manufacturer, Thales, will begin working with the SFMTA on the second phase that will assess the integrity of the existing cable and determine the extent of replacements necessary.

The agency expects to begin installation of the replacement cable in early November, which will require weekend overnight closures to install the cable in sections. The replacement is projected to take at least four months, Haley said.

Once the work is complete, delays will be reduced, Haley said, because trains will not have to operate in manual mode–at least not because of the need to splice damaged loop cable.

Patricia Decker, Bay City News

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