Designed by engineers J.A.L. Wadell and John Harrington, this bridge near 19th and Stewart Streets is the second vertical-lift bridge ever built crossing the Chicago River, and only one still standing. Near Chinatown over the South Branch of the river, this bridge was completed in 1915 for the Pennsylvania Railroad. The bridge is now owned by Amtrak and carries Metra and Norfolk Southern train traffic in and out of Chicago.
The bridge, which crosses the river at an angle of approximately 47 degrees, is designed with a skewed, rivet construction, Pratt truss roadway carrying double-tracks over the waterway. The weight of the moving span, tracks, operating equipment, and bridge house is approximately 1,600 tons. The bridge is 272 feet, ten inches long from center-to-center of the end posts, and just over 30 feet wide. The massive steel towers are 185 feet high, host walkways around the top of each, and allow the bridge to open to a maximum river clearance of 111 feet.
This vertical-lift bridge operates like an elevator employing 64 2¼-inch steel cables, eight on each corner, connected to the top of the steel truss roadway, and run over eight 15-foot diameter cast steel sheaves (or pulleys) atop the adjoining steel towers, connecting to massive concrete counterweights suspended above the approaches.
The bridge is so delicately balanced that it can be opened with two (No. 162 Westinghouse railway type) 220-volt, 300 horsepower motors geared to four cast steel operating drums employing 1⅛-inch steel operating ropes. Either motor can safely operate the drive mechanism, which includes a 50 horsepower gasoline-powered emergency engine capable of lifting the bridge to its maximum height in approximately ten minutes.
A small corrugated aluminum house atop the center span of the Pennsylvania Railroad Bridge doubles as a bridge tender house and protects the original operating equipment, which is still in use. Today the bridge is operated by remote control from a railroad switching tower at 14th and Lumber Streets, and monitored via channel 16 on VHF radio and remote video. This bridge adheres to traditional maritime law and opens on demand to water traffic, mainly due to its low clearance of just ten feet (compared with a standard 16½ foot river clearance), although occasionally an expected train crossing may force water traffic to wait as long as 45 minutes before the railroad controller reopens the bridge.