Metro has cleared a "significant step" in its quest to resume running trains automatically, instead of manually, the agency's general manager said Thursday.

The National Transportation Safety Board, or NTSB, has approved a tool that Metro created to monitor the train system in real time to prevent trains from crashing.

The approval offers nauseated riders hope that the jerky trips and abrupt stops that they suffer when trains are operated by humans, not computers, will end -- at some point.

General Manager Richard Sarles declined to give any estimates of how soon automatic train service could resume. He said the agency first needs to complete an analysis of its safety system, among other work. "It's a step forward in that direction," he said.

More than 36 years ago, the rail system was designed to be run automatically, with trains accelerating and slowing down based on commands communicated electronically from the tracks to the trains. Computers can run trains more efficiently, faster and brake more precisely than humans can. Riders get a smoother ride, and trains are less prone to back up. Metro used to run trains automatically most of the time, but operators were needed aboard for safety reasons, to open doors and to occasionally drive them manually.

However, since the 2009 Fort Totten train crash, the agency has been running all trains manually to avoid a similar accident. In that case, the automatic track safety system failed to see a train stopped on the track waiting to enter the Fort Totten station. A second train came barreling down the Red Line at full speed in automatic mode. The operator threw the emergency brake when the train came around a curve, but it was too late.

Her train slammed into the stopped train. Nine people, including the operator died, and 80 more were injured.

The NTSB investigation found Metro had been having problems with the track safety system for years, with thousands of alarms being ignored. The federal board called on Metro to come up with a real-time way of monitoring trains, as backup to the automatic track safety system.

The agency crafted a software program and has been using it to track trains throughout the system since December, said Deputy General Manager for Operations Dave Kubicek. Metro officials showed off the tool to Federal Transit Administration and NTSB officials earlier this year.

"This is a nice added layer in monitoring the system," Sarles said.

But Metro still needs to finish replacing every track circuit in the system, a project that was expected to take three years and cost $60.5 million when it began in 2010. The NTSB had called on Metro to replace all of the 1,482 track circuits exhibiting the same "parasitic oscillations" that prevented the train control system from seeing the stopped Red Line train.

The NTSB has 22 outstanding safety recommendations for Metro, some dating to before 2009. Metro said it has submitted information to close 12 of them but is still awaiting final word.