Trains' Newswire had two good articles on this 'Loss of Shunt' -
September 5 and
September 6.
"In mid-August, the latest installment of an ongoing series of tests was staged out of Canadian National’s Effingham yard in southern Illinois. The sessions, attempting to seek a permanent solution for locations where loss-of-shunt issues are ongoing, were attended by participants from CN; Amtrak; the Federal Railroad Administration; the Illinois and California transportation departments, and equipment vendors. More testing is set for September."
CN commented to Trains:
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n a lengthy statement to
Trains News Wire, CN says, “Extensive testing up to this point indicates that the random loss of shunt detection events experienced by single-level passenger equipment in the US is due to the absence of sufficient contact area between the wheels of passenger trains and the rail head.
A close-up of a rail head adjacent to a highway crossing at Chebanse, Ill. The wheel profile of a passenger car has a smaller contact area, which CN says contributes to loss of shunt. Bob Johnston
“The smaller contact area on the wheel profile of passenger equipment, combined with short and light trains, prevents the systematic sufficient transmission of current necessary to activate fully operational and FRA compliant railway crossings.”
Addressing why Superliners were required on the
Illini-Saluki route, the company asserts, “Due to the safety concerns, CN required either the use of heavier equipment or lowering the maximum operating speed at grade crossings for single-level equipment on this route. This was the responsible thing to do to ensure safe operations.” The speed restriction does not apply with Superliners, which were found to consistently shunt the circuit.
Loss of shunt is not caused by any host railroad’s infrastructure. Events occur where the combination of consistently trued wheel profile, light weight equipment, and minimal axle counts are present. It is false to claim it only happens on some routes, as any route with these aspects present would likely result in random loss of shunt events.”
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Current testing involves an antena based system:
"The latest round of tests investigating ways to ensure trains always activate track circuits — the process known as “shunt” — involves shunt-enhancing antennas mounted on both trucks of a state-owned locomotive in Amtrak service in California.
Here’s how the antennas work on F59PHI locomotive No. 2007: Using electricity supplied by the locomotive in an 11-mile test zone, a specially designed track circuit assistor (TCA) antenna is mounted near each running rail. The TCA antenna induces current into the rails, creating an electrical circuit for signal detection that may not otherwise be reliably transmitted through the train’s wheels. The idea is to create a dependable shunt on the locomotive to obviate the need for axle counts, speed restrictions, or certain types of equipment currently used to address loss-of-shunt issues."
It is still boggles my mind that this is a problem after all the trains operating on many railroads including lightweight RDC's, Turbo trains, and trains with single level equipment. I suspect the lawyers were involved and said crossing gates must work 100% of the time!
