In light of an Upper Darby subway crash earlier this year, the National Transportation Safety Board has recommended that SEPTA install cameras that face both outward at a train's route and inward on its operator.

On Feb. 21, a Market-Frankford Line train rear-ended another train in the yard behind the 69th Street Transportation Center, injuring three people. A third train was also damaged in the derailment. After the crash, the operator of the train that caused the crash said he didn't remember what happened.

The NTSB stated Thursday that inward- and outward-facing cameras would have been invaluable in determining what caused the collision.

"In 47 of the 64 rail transit accidents the NTSB investigated between 1976 and 2015," said Robert Sumwalt, the NTSB's chairman, "audio and image recorders would have greatly helped in learning what happened by documenting and preserving data describing the actions and conditions leading to an accident."

The NTSB also recommended that SEPTA publish a semiannual report detailing its progress in installing the cameras.

SEPTA said it has  a contract with a company that installs cameras and expects to have the devices installed on elevated and subway trains by the end of the year.