Friday, June 30, 2017

Passenger Train Evacuation on Elevated Guideways

Following a major subway derailment in New York City, Michelle Matsuo asked many questions on a transit forum. I answered them below.

In Honolulu, if a train derails, will it hurtle off the guideway?  
Normally it will not and HART route alignment, unlike Chicago's L for example, does not have 90 degree turns. While unlikely, under extreme conditions a HART train can jump the tracks and fall off the guideway.

If there is a malfunction somewhere on the track, will a train get stuck between stations?
If a train breaks down, then it will be stuck. A following train may be commanded to push the broken down train to the nearest station.

If there is grid power loss, then nearby stations have generators to provide enough power to pull the train to the nearest station.

Do the windows open?  If they do, is it enough to keep people from cooking in the train?  
Typically windows do not open. There may be vents that can be opened.  Unless there's loss of grid power, the train may break down mechanically, but the a/c should still be functional. If the a/c dies, then people will need to be removed within a few minutes during hot conditions.

If they open, then will people be tempted to walk along the guideway, and will they get electrocuted by the third rail? 
There is an emergency walkway in the middle as shown in the picture below. In an emergency with smoke, extreme heat or other need to abandon the cab, people should be advised to exit on the narrow walkway, walk a short distance away from danger, then sit down and wait for rescue. In such extreme conditions, walking on the track may be necessary and can be safe as long as people stay well clear of the third rail (see gray line on the left side of the picture.) Given the design of HART guideway, if evacuation of the passengers is needed along the guideway, then the situation will be risky for several reasons.

What is the repair protocol for the trains and the tracks?
At frequent intervals there are switches (see sample train track switch below) so trains can go from the left track to the right track (and vice versa) and in effect "overtake" the disabled train. Eventually the control room has to decide the best time and method to deal with the problem, such as sending crew for on-site repair or pulling the broken down train to the yard.  A disablement that cannot be fixed quickly on site will cause delays to the operations.

The tracks should be inspected and maintained on a schedule so that they do not generate failures during operations. These are usually done off peak or at night.

If the track is neglected, as at the Washington Metro, then multi-day closures of the line may be needed if the condition is deemed unsafe or difficult to fix at night. It may be still be possible for HART to run trains on a single track while the other track is being repaired, but intervals between trains will be long.

Apparently this is an area that is lacking sufficient attention, as federal guidelines seem to date back to 1985: Recommended Emergency Preparedness Guidelines for Rail Transit Systems.

A 2014 technical article A new approach for modelling passenger trains evacuation
procedures states: "In most emergency situations, a successful evacuation and rescue can mean the difference between life and death. In passenger trains, the crew are responsible for passenger safety." HART trains have no crew on board.

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