Earlier in the day of the accident, a switching issue forced dispatchers to reroute the Evanston Express to run counter-clockwise around the Loop instead of its normal clockwise route.

Because of congestion caused by this abnormal track sharing, the Ravenswood train would be required to stop short, waiting for the rerouted Evanston Express to clear before proceeding.

This resulted in the rear cars continuing to push forwards, pinning the front of the train against the waiting Ravenswood on the right-angle turn of the track.

As motor power continued to be applied, the first three cars (two Budd 2200 units and a single Pullman-Standard 2000) were pushed further upwards, until they jackknifed and fell off the tracks.

While "traces of THC" were found in one urine sample,[2] "the extent to which [Martin] may have been under the influence of marijuana at the time of the accident could not be determined by tests.

[1] As a result of the accident, the CTA forbade motormen to proceed past a red signal "on sight" without first getting permission from the Control Center.