Expert says safety devices might not have given train time enough to brake
As CTA officials work to repair tracks and platforms at the site of Monday's Blue Line crash, the decision to move safety devices at the O'Hare station means the current location isn't working, an expert said Thursday.
The National Transportation Safety Board is continuing its investigation into the crash that catapulted the front car of the eight-car train onto an escalator at 2:50 a.m. Monday. The operator of the train admitted she dozed off and woke up just before impact, the second time she fell asleep on the job, authorities said.
The train has been cleared from the station, and officials are looking to reopen some time this weekend.
Retired agency attorney John Plante, a Metra board director who specialized in risk and emergency management at the Chicago Transit Authority, said the CTA's announcement Wednesday that officials would move back safety devices called trip arms likely means they're "too close" to give trains enough time to stop.
"If they're moving it back down toward the entrance to the tunnel to provide more stopping room, apparently, they don't feel they have enough room at 25 mph," said Plante, referring to the speed the train was supposed to be traveling at when it entered the station area. The agency has said it would reduce speeds to 15 mph at the station entrance.
One focus of the NTSB investigation will be the sufficiency of the CTA's emergency preparedness as far as braking systems go.
CTA trains have three types of brakes: an electric braking system that uses traction motors (also known as dynamic braking); a friction braking system that uses disc brakes similar to those used in cars; and an electromagnetic track brake that clamps down on the steel rails and is usually used in emergency situations.
Normally when entering stations, operators use the electric braking system to slow the train down to 3 mph. Then, the friction brakes bring it to a complete stop.
To prevent trains overshooting the end of the tracks at the O'Hare stop, a device called a trip arm is located on the track about 41 feet from a large rubber and steel bumper at the station terminus. In the unusual event of a train going past the switch arm, it would activate a trip switch on the rail car that sets off the electric braking and the friction braking simultaneously. Together, this provides a higher braking rate, experts said.
Asked if the 41-foot distance was sufficient at a Wednesday briefing, NTSB lead investigator Ted Turpin said, "We don't know, we have to check. We're still looking at all the numbers."