The driver of a school bus struck by a fast-moving commuter train may have had as little as two seconds to react before the collision that killed seven students, a federal investigator said Thursday.

Investigators are trying to determine why the bus carrying 35 students was still waiting at a traffic light with its rear end over the tracks when the train came through Wednesday.

The bus driver, Patricia Catencamp, told investigators she never saw or heard the train until impact, and didn’t hear any warnings from students. She also said the traffic light never turned green.

“There was a considerable amount of noise in the bus,” National Transportation Safety Board member John Goglia said Thursday night. “She did not hear a (train) horn.”

Five students died Wednesday, and two more died Thursday after they were taken off life support. Eight other students remained hospitalized, one in critical condition.

Investigators tested the traffic light Thursday and were seeking police phone logs to check for complaints about the signal.

“The timing doesn’t appear to be proper,” Goglia said.

The NTSB said approaching trains trip sensors embedded in the tracks that prompt warning gates to lower, lights to flash and bells to ring. At the same moment, the traffic signal begins to change, eventually turning green to allow vehicles to clear out of the way.

Goglia said tests indicate the light would turn green 18 seconds after the train hit the sensor. Trains traveling the route in the last two days typically have taken 20 to 25 seconds from the time they trip the sensor to the time they reach the crossing, Goglia said.

That would leave just two to seven seconds after the light turned green for the driver to get the bus in gear and move off the track before the train hit.