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- 29 - The engineer of train 720 did not comply with the yellow aspect displayed by Signal 3-3.60. The message conveyed by the aspect was "Caution! Train ahead." The engineer, however, was not particularly concerned that there was a train ahead—it was ahead every day.

The signal system was working as intended but did not prevent the accident. Traffic scheduled through the accident area during rush hours resulted in very close headways. Trains were commonly operated under the authority of red and yellow aspects. This system was safe as long as the rules were obeyed; there was no margin for disrespect. There are signal systems available (e.g., cab signals, automatic train control, automatic train stop) that place less reliance on rule enforcement to ensure safety.

The reverse movement of trains into previously vacated signal blocks was incompatible with the scheduled 2 to 3 minute headways of ICG commuter operation and the time required to implement flag protection. The more logical procedure after a train overruns a station more than a train length or overruns a signal was to continue on to the next station. The Safety Board's Recommendation No. 2 included as part of Appendix F proposed that ICG commuter trains be restricted from reentering a signal block unless protected by train order.

Federal Railroad Administration regulations cover the methods of installing signal systems. However, regulations specifying the type of signal systems to use for particular circumstances are minimal. These requirements seem as important as installation and maintenance requirements. The objectives of a signal system must be defined if safety is to be achieved through regulation.

Crash Factors

Each of the "old" cars and Highliners had a heavy underframe upon which a lighter superstructure was built. The underframes, designed to withstand coupling shocks, carried couplers at either end. The design of the couplers was so specified that, when joined, the couplers and the end design would prevent override in a collision.

When the two trains collided, the couplers on both trains functioned as intended, and there was no overriding of one car by another within either train. However, the coupler on the head of train 720 was displaced downward, which broke the coupler carrier. This destroyed any anti-climbing capability which might have existed between the two dissimilar cars. When the coupler ends came together, the direction of least resistance was upward. The wheel flanges and truck centerpin resisted movement sideways. The normal weight-bearing strength of the truck resisted downward movement. Only the weight of the front end of the car body resisted upward movement, because the front truck was not secured to the car body. This upward movement appears to have been the critical factor which placed most of the fatalities and serious injuries in the Highliner car.