I've never been good at math Wrote:
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> If the skid marks were 125 feet long, but began
> 425 feet before impact, doesn't that leave a 300
> foot gap between the leading braking wheel and the
> rear of the impacted train?

No, it's like BOB2 described.

Refer to the second paragraph of the NTSB's June 25th press release shown below. It's a little clearer.

[ntsb.gov]

NTSB Advisory
National Transportation Safety Board
Washington, DC 20594
June 25, 2009

NTSB ISSUES UPDATE ON INVESTIGATION INTO COLLISION OF TWO METRORAIL TRAINS IN WASHINGTON, D.C.


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The National Transportation Safety Board continues to make progress in its investigation of the June 22, 2009, accident involving the collision of two Washington Metropolitan Area Transit Authority (WMATA) trains on the Red Line in Washington, D.C. The Board has developed the following factual information:

Investigators found metal to metal compression streak marks on both rails of the track for about 125 feet ending near the approximate point of impact, consistent with heavy braking. [Emphasis added]

Investigators conducted tests at the accident site last night with a similar train and found that when the train was stopped at the same location as the stopped struck train, the train control system lost detection of the test train.

The train control system is complex and will require a thorough investigation of all components. Investigators are continuing to examine trackside circuits and train control system data to understand how the train control system functioned on the day of the accident.

Investigators have collected recorder data from the struck train. Data was recovered from eight of the nine recorders on the struck train. Data could not be downloaded from one recorder. Two of the eight recorders did not contain data related to the accident; data collection ended before the accident for undetermined reasons. The accident data is now being examined by investigators in the Safety Board's laboratory. The striking train did not have any onboard accident data recorders.

The operator of the struck train was interviewed earlier today. He said that he operated his train in manual mode during his entire shift that afternoon. He said that he saw a train in front of him and stopped to wait for the train to clear. While stopped, he said that he felt a hard push from behind.

Investigators are continuing to document evidence at the accident site and intend to conduct sight distance tests, using similar trains to those involved in the accident. Parties to the NTSB investigation include WMATA, the Federal Transit Administration, the Amalgamated Transit Union, and the Tri-State Oversight Committee.



Media contact: Bridget Ann Serchak
202.314.6100
bridget.serchak@ntsb.gov