That’s just one of the things that Michigan Department of Transportation engineers learned in last year’s “bridge slide” – a neat new procedure for overpass construction that limits traffic tie-ups.
MDOT, its subcontractors and the building trades performed three bridge slides last year, two at the same site in Mecosta County, and the third and most visible, at M-50 (Alden Nash Ave.) over I-96 in Lowell Twp., east of Grand Rapids.
Under the procedure, building trades crews started by placing new bridge footings into the ground at and next to the existing bridge structure that is to be replaced. Then on those footings, supports for bridge construction and the new slide rails were installed. To support the new bridge, beams were set over I-96. Then the concrete deck was poured and the bridge railings were constructed. When the new span was complete, the old deck was demolished and the new deck was slid into place.
The new bridge was slid into place Oct. 18, and the entire job was complete in November.
“During a four or five month project, which might have led to continual bottlenecks because of reduced lanes or a complete closure of M-50, we were able to complete the project with closings on only two weekends,” said MDOT spokesman John Richard. “It makes for a much more interesting project, and it’s much easier on traffic.”
The bridge slide isn’t new in the U.S. – Michigan is about the 10th state to try the concept. The big dates on the project’s calendar were overnight on Oct. 17-18 – the sliding of the new span began that Friday night and was completed early Saturday morning. Three pushing motors pulled the structure and one motor pushed it. The bridge was moved atop bearings that were supposed to use a glycerol-based lubricant, but the cold weather that night coagulated the stuff. So someone made a trip to a local store, and returned with several bottles of Dawn dish soap. “It worked well, in fact, they said the Dawn worked even better than the lubricant that they had,” Richard said.
The procedure costs a bit more than the conventional method of demolishing part or all of a bridge and then replacing it in place, but Richard said it’s worth it, with all the savings in motorists’ gas, time and frustration. A bridge slide is planned near Lansing in 2015.
“You can’t do it everywhere, especially in urban areas, because of space limitations,” he said. “But with these projects we heard from a lot of motorists who were impressed with the job and thankful that their drives weren’t disrupted.”
THE NEW BRIDGE DECK at M-50 over I-96 is shown after it was slid into place. The new structure was wider by 33 feet. Traffic was first diverted to the new bridge in its temporary location while the old one was demolished. Photo courtesy MDOT Photography Unit