Investigators looking into Monday's subway accident in Washington are examining the automated system that was apparently in control of the train that crashed into another train, killing nine people.

National Transportation Safety Board investigator Debbie Hersman told reporters Wednesday that the computer-operated system is designed to maintain space between trains and stop them in emergency situations.

Examining switches on tracks

She said investigators are examining switches in the tracks and other automated systems that send signals to the trains. Hersman says they will also pump air through the brakes of the train to determine how they were functioning at the time of the crash.

Investigators say there is evidence the operator attempted to stop the train before impact. The train's operator, Jeanice McMillan, is among the nine people killed in the crash.

Hersman says investigators also hope to examine the data recorders that were on the the train that was struck.

Cellphone records will be examined

She says the NTSB will examine McMillan's cellphone and text-messaging records, as well as her blood samples and work schedule.

Two recent crashes, one of a commuter train in suburban Los Angeles and one of a trolley in Boston, occurred while operators were using their cellphones or sending text messages, but the general manager of Washington's transit system says there is no evidence that McMillan was doing that at the time of Monday's crash.

The accident happened near an above-ground station in northeast Washington.  The impact of the crash was so hard the lead car of the moving train was sliced open, vaulted into the air and landed on top of the rear car of the other train.  

The cars that made up the moving train were among the oldest in the Metro transit fleet.  Hersman says the NTSB had recommended the cars of the older train be phased out due to safety concerns, but transit officials say they lacked the money to purchase replacements.

Hersman says the older train did not contain data recorders.