Stephen Rees's blog

Thoughts about the relationships between transport and the urban area it serves

The Washington Subway Crash

with 2 comments

This week’s events in Washington were shocking – and are also very hard to understand.

To put the apalling death toll in the subway train crash into perspective here is the death rate by mode in the US, courtesy of Todd Littman

US Death Rate By Mode The Washington subway would be included as “heavy rail”

Washington has a computer controlled train control system – and it now appears that this failed.

The National Transportation Safety Board (NTSB) confirmed that train control systems failed during investigative tests being carried out to determine the cause of the Washington DC train crash on Monday that left nine dead.

Two Washington Metropolitan Area Transit Authority (WMATA) trains collided on an above ground section of the Red Line metro railway in Washington DC at around 5pm local time when a moving train crashed into the back of a stationary one.

THE NTSB investigators have conducted tests at the accident site with a similar train and found that when the train was stopped at the same location as the train which was crashed into, the train control system lost detection of the test train.

Now investigations have to continue to determine why it “lost detection” – but also it will be necessary to determine if that would have made a difference

The operator of the struck train said he had been driving the 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.

So it would appear that trains were being driven on “line of sight” – not using the train control system. Since “the striking train did not have any onboard accident data recorders” and the driver of that train was killed, that may not be possible to establish with respect to the striking train conclusively.

+++++++++++++

UPDATE Sunday June 28

The Washington Post is now reporting that the striking train was under automatic control – and the driver used the emergency brake properly.

+++++++++++++

On systems like SkyTrain and the Canada Line, there are no line side signals since the train control system uses a “moving block” principle to keep a safe distance between trains. When that system is overridden – for example to keep train staff familiar with emergency procedures – the train speed is restricted to half normal speed while under manual control. The only collisions that have occurred on these systems have been when the trains were being driven manually.

DLR under driver controlNormally the DLR operates automatically under the Alcatel system. But for “train captain” training purposes, they are run under operator control at half speed and “line of sight” every so often

The Docklands Light Railway (above) uses the same type of Alcatel system that SkyTrain and the Canada Line use. (The Washington system was supplied by Alsthom but it is not clear to me from this document if it is similar to the Alcatel system.)

Whatever system is installed, it is only going to work if it is in use. And one of the weaknesses of the US transit funding system is that  money is provided by the federal government to build things, but not to keep them in a state of good repair. One of the common features of the myriad press reports on Google of this crash is that the Washington subway system as a whole needed upgrading. This was also the issue that was identified in a recent highway bridge collapse – it’s not just about transit. Already senators are calling for more money for system upgrades but the “systemic problem of the billions needed each year to keep them operating” is still not being addressed.

Anymore than it is here.

Written by Stephen Rees

June 26, 2009 at 11:08 am

Posted in transit

2 Responses

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  1. It is very difficult to comment after disasters, but I had a ‘gut’ feeling that the signaling system was somehow at fault. Washington’s metro is not all that old and had automatic train control.

    A US transit specialist told me that if ‘line of sight’ is used on the metro, then reduced speeds are enforced, just like SkyTrain.

    SkyTrain’s system is a ‘moving block’ system, which must, by its very operation, have added safeguards, especially if its driverless.

    What I have read is that the Washington metro had a fixed block system ATC.

    The problem inherent with all signaling systems is age and maintenance issues and if proper ongoing maintenance is not done, problems arise. Of course when a signaling system ages, maintenance costs rise.

    SkyTrain is feeling the effects of 25 years of operation and regular users who correspond with me have all claimed that there are many more ‘down’ times on the system than before. 2 minutes here, 3 minutes there, it all adds up and if this is happening on a regular basis, it must be a contributing factor in overcrowding, especially if one is operating 60 sec. to 90 sec. headways!

    What was the ‘flavour of the decade’ in the 1970’s, automatic operation (driverless) is avoided on all but the heaviest used metro lines as studies have shown that automatic transit systems are only cost effective on routes that cater to over 20,000 persons per hour per direction.

    The canard that the Washington metro cars were old, I think, was to camouflage the fact that the signaling system was at fault, which could make liability issues a lot easier to define, resulting in hefty settlements.

    Malcolm J.

    June 29, 2009 at 7:41 am

  2. [...] in their Breaking News feature provide some more information on the probable cause of the fatal crash on the Washington DC subway. Metro officials said the malfunction that appears to be at the heart of last month’s deadly [...]


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