The safety system that automatically stops Metro trains from rolling backward could not have prevented a crash last week at Woodley Park because both trains involved were being run manually, transit officials said.

The National Transportation Safety Board is continuing to investigate a runaway train that slid backward Nov. 3 and slammed into a six-car train carrying 70 passengers at the Woodley Park-Zoo/Adams Morgan Station. Investigators are examining the actions taken by the novice operator of the runaway train, including whether he applied brakes too late.

Metro officials said yesterday that the rollback protection would not have been in effect during the crash because both trains were in manual mode, and the rollback protection system has no control at such times. The protection system relies on electronic signals built into the track to recognize when a train is moving backward and notify computers on the train to engage the brakes.

Metro trains are designed to run automatically, with computers controlling speed and braking. But it is common for operators to be directed to run trains manually, when a greater degree of human control is needed. For example, operators will run trains manually when tracks are icy or where speeds have been reduced temporarily.

Last month, as a way to sharpen train operators' skills, Metro managers started requiring all operators to run trains in manual mode during off-peak hours on weekdays and all day on Saturdays and Sundays. Last week's crash took place during one of these periods.

Metro officials said trains will continue to be run in manual mode. But they sent a bulletin to train operators to remind them about proper braking procedures. "We are not asking our train operators to do anything differently," said Fred Goodine, Metro's assistant general manager for safety. "We are simply providing a reminder to them about proper braking procedures. We are asking them to continue to do exactly what they have been trained to do. It is perfectly safe for us to operate trains either manually or automatically."

Operators have several ways to bring a train to a stop. They can use a master control lever to apply several levels of braking power, similar to downshifting a standard transmission automobile. If they simply let go of the master lever, that applies brakes as well. They also can hit a round, red emergency button on the cab console known as a "mushroom." As a last resort, operators can apply a parking brake.

Operator Lamont Lewis, who has seven months of experience on the job, told investigators he applied the maximum braking power using the master control lever, then put the train into drive gear and tried to move it forward at full power. He said he got no response, and the train continued to slide backward, said Debbie Hersman of the NTSB.

Lewis told investigators that he then released the master control lever, hit the mushroom and felt the train come to a stop. What he did not realize, Hersman said, was that his six-car train had plowed into another train. Metro estimated that Lewis's train was traveling at 30 mph.

Twenty of the 70 passengers aboard the other train were sent to hospitals with minor injuries.