The New Jersey Train's Data Recorder: What It Can Tell Investigators

— -- Investigators now know the speed at which a New Jersey commuter train crashed into the Hoboken Terminal on Thursday -- leaving one person dead and 114 injured -- due to the recovery of a data recorder from the locomotive car at the rear of the train, sources tell ABC News.

But a second recorder that was located in the train's "controlling cab" at the front of the train has yet to be recovered due to safety concerns at the crash site in Hoboken, New Jersey. The front of the train was the most severely damaged in the crash, and in addition the station's canopy fell onto the front car, making it difficult for investigators to access. The National Transportation Safety Board hopes to recover the second data recorder today if the area is safe enough for investigators to get it.

Investigators said they may release some information publicly as soon as today.

What the recorder could tell us

Train data recorders differ significantly from those on airplanes. While data recorders on a commuter train and freight train can vary in function, most only record a train's technical operations and not voice data. According to investigators, the NTSB hopes to retrieve pertinent information from the data recorder besides the train's speed prior to and at the time of the accident, such as: the train's throttle position; if the brakes were applied and whether the engineer used standard brakes or emergency brakes; and whether a horn was used. When the data recorder located in the controlling cab is recovered, it may also tell investigators what signals and lights were visible prior to the accident.

The problems investigators face

But as with flight data recorders, possible challenges are at play. Although train data recorders have protective material around them to withstand an accident, the recorder can still malfunction and fail to record data or can be so badly damaged that it is difficult to extract data from it.

In some cases, the NTSB will bring in the manufacturer of a train or its data recorder to assist federal investigators with downloading and analyzing the data.

It’s not all about the recorder

Experts are quick to note that they rely on more than the data recorder during the investigation process.

"Even if we don't have all the information from an event recorder, we can still gain additional information from examining the track, examining the train itself," and looking into other things related to the accident, NTSB Public Affairs Officer Keith Holloway told ABC News.

Holloway said his agency will also look at whether the train's data recorder correlates to other information from the accident scene, such as security-camera footage and witness testimony.

ABC News' David Kerley contributed to this report.