NTSB: A Simple Signal Change Could Have Prevented Amtrak 188 Crash
Railroad engineers on Amtrak have three things that determine how fast their trains can go. One is the speed governor on the locomotive, which determines the train’s absolute maximum speed. Another is the train timetable, which lists the normal speeds along the route. The third is the in-cab signals, which can force trains to slow down if they are approaching a speed-restricted section of track. This last item is known as “automatic train control.”
Trains approaching the 50-mph curve at Frankford Junction from the north are forced to slow down to 45 mph by a restrictive cab signal far enough away to bring the train down to that speed by the time it hits the curve. Prior to the crash of Amtrak train 188, trains approaching the curve from the west were not.
According to the National Transportation Safety Board’s Signal Group Factual Report (below), the reason they were not is because the top speed posted in the train timetable for the straightaway leading into “Shore interlocking,” the last signal west of the curve, is below the “overturning speed” for the curve — that is, the speed at which a train taking the curve would tip over and derail.
The overturning speed for the Frankford Junction curve is 98 mph. The normal speed for the straightaway leading into it from the north, as given in the timetable, is 110, but the normal speed for the straightaway entering it from the west is 80. Therefore, Amtrak reasoned, since no train approaching Shore interlocking from the west would be traveling as fast as 98 mph, there was no need for the signal at that point to force a slowdown by restricting the train’s speed through the in-cab signals.
The trouble with this reasoning is that the timetable speed is simply a number on a sheet of paper. Without a restrictive signal, the only actual limit to how fast a train may go is the speed governor, which permits a top speed of 125 mph.
Amtrak 188 was accelerating past the timetable speed as it approached Shore interlocking. Locomotive event recorder data shows the train passed the overturning speed about 19 seconds before it entered the curve and peaked at 106 mph when engineer Brandon Bostian initiated an emergency stop about four seconds before derailing.
Amtrak had added the restrictive signal on the southbound tracks after a 1991 crash at Boston’s Back Bay Station led it to reassess its signaling practices on dangerous curves. As a result of the wreck, the report states, “Amtrak is now in the process of reviewing what was done in 1991 and intends to modify the signal system such that trains traveling eastbound towards Shore interlocking will receive a signal downgrade to Approach Medium ensuring that their speed will be down to, or below, the timetable speed for the curves east of Shore before reaching them.”
In addition, the report states that Amtrak expected to meet the December 31, 2015, deadline for implementing positive train control, a communications-based speed control system, along the entire Northeast Corridor from New York to Washington. So while it’s cold comfort to the victims of the Amtrak 188 crash and their families, a wreck like this one won’t happen again.
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