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T says rubber seal failed, leading to Green Line derailment today

Print | Comments () Posted by John Ellement April 13, 2011 04:19 PM

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David L. Ryan / Globe Staff

Shown is the dislodged rubber seal that the MBTA believes was responsible for the Green Line derailment today.

By Eric Moskowitz, Globe Staff

A Green Line trolley derailed on South Huntington Avenue today, forcing police to close the street to traffic for about an hour and a half and prompting the T to suspend trolley service between Heath Street and Brigham Circle for nearly five hours.

The trolley was headed inbound on the E branch, approaching the right turn from South Huntington onto Huntington Avenue, when it skidded partially onto the pavement about 100 yards shy of the intersection, at about 9:30 a.m.

No one was injured, and the trolley sustained minimal damage, T officials said.

The derailment appeared to be caused by a dislodged rubber seal, a long rubber strip that abuts the rail where the track is embedded in asphalt.

The seal normally provides a passageway for the flange on the trolley wheels and also allows track workers easier access to the track for repairs than if the track was fully encased in pavement, said Brian Dwyer, the MBTA's director of light rail operations.

"What we believe happened is that [seal] popped up and just gave the train wheel enough of a lift that the wheel lost its normal relationship with the rail, and the flange of the wheel ended up on top of the rail," Dwyer said. "It rode for a little while and then it came up off the top of the rail onto the asphalt."

The lead car, No. 3631, remained fully on the tracks even as the front wheels on the rear car, No. 3884, popped off and that trolley swung out to the right, with the two cars still coupled together.

The busy route is served by both the E branch and the MBTA's Route 39 bus, so the evacuated trolley passengers were directed to the next bus.

Boston police and transit police initially closed the road to non-bus traffic before rerouting it through cones to a single lane in each direction.

Power and maintenance of way workers from the T shut off electricity to the overhead catenary line and cut away the trolley's pantograph -- the device that connects it to the power supply -- so that they could hoist the car back up onto the track using hydraulic equipment, Dwyer said.

The trolley was back on the rails a little after noon, but the T remained on site for another two hours, making wire, track, and pavement repairs, Dwyer said.