The National Transportation Safety Board has not yet finished its investigation of the crash on the DC Metro which killed 9 people on June 22. But the outlines of a possible explanation are emerging.

The crash happened at 5 p.m. as a Red Line train was heading down into Washington DC from Tacoma Park, Md., and slammed into another train that was stopped by the Fort Totten station. The force of the crash was such that the first car of the moving train ended up on top of the last car of the stopped train. The operator of the moving train and eight other people were killed, and a number injured. Had the accident happened when the train was going the other way, it would have been full of rush hour passengers and the death and injury toll might have been much higher.

Investigations by the NTSB quickly revealed that in 2006 it had told the agency that runs the Metro, Metropolitan Washington Transit Agency (MWATA) to either renovate the antiquated cars, built as early as 1974, or replace them. This was not done, partly because of some complex business relationships between MWATA and a major bank. This information caused anger in the Washington area at the administration of MWATA.

However, the NTSB investigation has since found evidence that not the cars themselves, but the electronic system that keeps cars a safe distance apart when they operate automatically during rush hour, may have been the defective element which caused the crash.

The Washington Post reported on July 7 that this computerized signaling system installed at the level of the tracks may have been malfunctioning sporadically. The malfunction may have been missed because it was an episodic and not a constant problem.

The system would have told the train that was in motion that it had a clear track ahead of it and thus the train would have automatically increased its speed to more than 50 miles an hour, too fast to be stopped by the last minute emergency braking attempted by the operator when she realized what was happening.

Other metro train systems have the same kind of electronic controls, but they are backed up by an additional fail safe system, which appears to have been absent from the DC system.

Jackie Jeter, president of Amalgamated Transit System local 689, whose members operate the DC Metro trains, called for more control by the operators over the functioning of trains in such circumstances. She says she has heard from her members about similar problems in the past, which have not been corrected.

Jeter demanded that MWATA provide assurances to drivers that the causes of the failure which caused the June 22 crash be corrected.