[Marxism] Train Collision in DC

[S. Artesian]

Those of you interested in the events in DC:  NTSB has issued the following 
information in a press release:

"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 full text of the release is here: 
http://www.ntsb.gov/pressrel/2009/090625.html


The circumstances as described by the NTSB are the worst possible failure: 
a system failure to detect, identify, register track occupancy by a train, 
thus allowing a following train to operate at the normal, maximum authorized 
speed.  This is every railroader's nightmare.  I know it used to wake me up 
at night, making me calculate and recalculate signal design distances, train 
braking rates, and reviewing the results of safety verification testing of 
our signal system.

I am not sure if WMATA uses classical track circuitry to to detect train 
occupancy and maintain safe separation of trains-- track circuitry actually 
uses the rail to conduct a current and then registers occupancy when the 
wheels of a piece of rolling stock  create a "short-circuit" causing voltage 
to drop--, or if WMATA signal achitechture is based on some form of 
individual train communication to wayside signal controller processor, or a 
central office signal controller processor, in which the train identifies 
itself through continuous transmission of a radio frequency signal, 
identifying itself to the signal control system to establish occupancy and 
transmit the necessary speed limitations to following trains.

This sort of failure, known historically when wayside fixed color, fixed 
light signals were used, as "false clear,"  calls into question the 
integrity of the entire signal system and its ability to maintain safe 
separation of trains at all times under all circumstances.

Under these conditions, and particularly when line of sight is obstructed by 
curves, elevations, structures, etc. the operator of a following train can 
do nothing except apply the brakes in emergency and hope his/her survivors 
get a good lawyer.

Terrible tragedy.