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- 18 - performance of the motorman of the Lake-Dan Ryan train and his testimony about his understanding of the rules, the Safety Board concludes that he was not adequately counselled by one of the roving supervisors when bulletin S-511-76 was first issued.

Even though the "responsibility log" insures that an employee reads the new rules or changes, it does not insure that he understands the rule nor how it should be applied. This can be accomplished only by reviews or instruction of the rules with each employee.

The extent that the motorman may have been under the influence of marijuana at the time of the accident could not be determined by tests. Because of the nature of THC and its chemical behavior in a human body, tests could conclude only that the operator had ingested marijuana at some time before the accident. There is no scale available to relate levels of THC or its effect on the behavior of individuals.

The present agreement between the CTA and the operator's union to use only an employee's record for 1 year to determine his past performance for disciplinary purposes does not provide a sufficient time span for management to properly evaluate an employee and to decide if he is a potentially high-risk employee. The Safety Board believes that more than 1 year of an operator's service record should he considered in a performance evaluation. If the Lake-Dan Ryan motorman's entire service record had been used as a basis for his performance evaluation, it may have conveyed to the CTA that he needed help in some areas and that he may have been a potentially high-risk employee.

A dynamics analysis based on the fact that the Lake-Dan Ryan train moved the standing Ravenswood train forward 25 feet when they collided indicates that the Lake-Dan Ryan train was moving at 9.5 mph into the curve. The resulting potential energy and the location of the cars in a sharp surve led to jackknifing between cars. The dynamic forces reacted greatest between the first and second cars, since their coupling was in the sharpest portion of the curve. When these cars began to jackknife because of the forward force from the rear, they began to fall over the side of the elevated structure. The second car apparently pulled the first car backward causing it to fall; while it was being pushed by the third car, the second car forced the third car to the right. The third car pulled the fourth car off the structure and the fifth car apparently was being pulled off by the fourth car when it was stopped by the station platform.

Same impact energy was absorbed by the draft arrangement of the cars on each train and a considerable amount of energy was absorbed by the jackknifing of the cars. Even so, the cars in the Lake-Dan Ryan train moved the Ravenswood train ahead. This force appears to be