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Upon impact, about 5:27 p.m., the first car of the Lake-Dan Ryan train began rocking slowly from side to side, moved slightly back, and then fell from the track structure. Several witnesses reported seeing a high-intensity, electrical arc flash and hearing a loud noise at that time. The next three cars reportedly stopped and then turned over slowly and fell from the elevated structure. (See figure 3.)
Train propulsion power, which was supplied by a third rail, was not interrupted completely at the time of the accident. Electric power is fed to a power section from both ends but only one circuit breaker for the power section on the outer track opened momentarily at 5:27 p.m. at the time of the accident. Power was ultimately cut off for both tracks about 5:46 p.m. One southbound train on the inner track passed the accident site about 10 minutes after the derailment. The motorman of that train moved past the site under the direction of a company official, although the central controller had ordered all trains in the area to stop and remain standing.
The motorman of a train following the Lake-Dan Ryan train operated his train to within an estimated one-car length of the rear car of the derailed train. He said he was able to move that close on a cab signal indication which he identified as an "amber 15 or Yellow 15."
The accident occurred at the northeast corner of the "loop" where the elevated track structure turns west from Wabash Avenue to Lake Street. (See figure 1.)
The tracks are laid on an elevated steel structure approximately 21 feet above the street. Six hundred volts d.c. electrical power is supplied by a third rail for propulsion on each track. The 6-inch by 8-inch crossties are laid on steel girders which form part of the elevated structure. The 90-pound, 33-foot rails for the main tracks rest on 10-inch, flat, single~shoulder tie plates. Each rail is fastened with two spikes per crossties and was laid in 1967. There are two 6-inch by 8-inch timbers secured on the ends of the crossties on the outside of each track, perpendicular to each crosstie. The main tracks are standard 4-feet 8 1/2-inch gage but the curve at Wabash and Lake is one quarter inch wider.
Between the running rails in the curve are two supplemental rails. A horizontal restraining rail bent to the radius of the curve is mounted along the inside of the low rail. It is laid on its side with a nominal spacing of 1 7/8 inches from the running rail. The back of the car wheel contacts the restraining rail so there will be added resistance against centrifugal force. Another guard rail is located 7 inches from the outside of the high rail to protect against derailment.
