Dozens of people were injured when a train left a CTA rail yard and crashed into another train with passengers in the western suburbs.
Federal investigators wrap up their investigation into Monday's train crash on the Blue Line after getting a close look at the trains involved.
They find there should be measures in place to prevent future incidents.
Their recommendations to CTA relate to preventing out of service trains from being powered on.
In a recommendation Issued today the NTSB found trains routinely powered on. But CTA refutes that claim.
"We power up trains prior to them leaving for revenue service. That can be a handful of minutes, it could be an hour, but we do not routinely leave on, we don't not routinely power on trains that are awaiting service," said CTA spokesman Brian Steele said.
On Monday morning a train awaiting repair service collided with an in-service train at the Blue Line's Harlem stop. Thirty-three passengers were injured.
Investigators say the out of service train had power and began moving onto a main track downhill nearly a mile.
Investigators find the train's emergency brake would stop the train momentarily but because the master controls were left in a setting that prohibited constant braking.
The NTSB made an urgent recommendation to CTA to: "Review their operating and maintenance procedures for stored unoccupied cars to ensure the propulsion and brake systems are left in a condition that would not facilitate unintended movement."
CTA already had issued a bulletin to maintenance and operations workers advising two new precautions with defective cars to disconnect power between cars and disconnect battery power to cars.
DePaul transportation professor Joe Schieterman says the new procedures can prevent runaway trains.
"The good news here is that it was a preventable problem that appears to be equipment that was unattended that picked up power, that picked up gravity motion that led to an accident," Schieterman said.
There will likely be no more comment from the NTSB as they will leave Chicago and go on furlough with the rest of the federal workers.