WASHINGTON — Investigators are looking more closely at a stretch of track near the site of a deadly commuter train crash after finding abnormalities Wednesday in equipment that detects passing trains and transmits speed and stop commands.

Equipment along a 740-foot stretch of track failed to recognize a device that simulates the presence of a train during the tests, said Debbie Hersman of the National Transportation Safety Board, which is leading the investigation into the crash that killed nine people during the Monday evening rush hour. Five other stretches of track, or circuits, near the Maryland state line showed no problems.

“Whether trains are operated in automatic or manual, these circuits are vital,” Hersman said. “We’re particularly interested in the speed commands that might be sent from that circuit when there’s a train standing on that circuit.”

The deadliest accident in Metrorail’s 33-year history occurred when a train plowed into another train that was stopped. The moving train was controlled primarily by computer at the time of the crash, but there is evidence the operator, Buffalo native Jeanice McMillan, 42, tried to slow it down. She died in the crash.

Hersman said inspectors found 300 to 400 feet of markings on the rails, indicating some emergency braking took place before the crash. Hersman also has said the emergency brake control on the moving train was found pushed down, though it’s not clear how or when that happened.

She said investigators hoped to interview the other train operator today, after his release from the hospital.

The cars destroyed in the crash included some of the oldest in Metro’s fleet. Federal officials wanted them phased out because of their tendency to compact in a crash, but Metro officials said the agency has lacked the money for replacements.

A union representing Metro transit workers also demanded changes in safety procedures. Jackie Jeter, the union’s president, said cars from the aging series involved in the crash should be placed in the middle of trains, rather than at the front or back because they are less stable.

The union also asked that operators be allowed to choose whether to use the automatic mode, which is typically employed during rush hour. Jeter demanded that Metro officials not mandate speeds at which trains should travel, saying operators were being pushed to move too fast.

A Metro spokesman said it was considering the union’s demands.

Metro says it needs $12 billion over the next 10 years to maintain services and replace aging equipment such as the older railcars. It says the federal government should contribute because its trains serve the capital, and many riders are federal workers.

Last year, Congress approved $1.5 billion in funds over 10 years, but with a condition that the District of Columbia, Maryland and Virginia match the amount. Now that all three jurisdictions served by Metro have agreed, Congress can move forward, officials said.