The CTA,  not Metra, will replace three deteriorating overpasses in the next year. Above, foreground pillars are Metra, and the rear ones, CTA.

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By the end of next year, Purple Line trains may pass more smoothly over Greenleaf, Dempster and Grove streets. The Chicago Transit Authority has begun work to replace deteriorating retaining walls and unsightly but necessary shoring there and along Chicago Avenue and will replace the bridge spans over those three streets.

At a joint Third and Fourth Ward meeting held last week at Nichols Middle School, Paul Schneider, director of the City of Evanston’s transportation department, and Bill Whittaker, general manager of construction for the CTA, gave an overview of the scheduled repairs and expected inconveniences of the project.

“The viaducts and the retaining walls are about 100 years old,” said Mr. Whittaker. “It’s time to replace them.” At Greenleaf, Dempster and Grove streets, he said, CTA will replace the overpasses with longer steel bridge spans, replace tiles, rails and ballast on the new bridges and relocated some signals and communication cables.” At ground level, CTA will install new sidewalks, fencing and landscaping and will replace the timber retaining wall by the Jewel Food Store north of Greenleaf Street and rehab the retaining walls along Chicago Avenue, he said.

Four caissons, one on each corner, will be installed in each of the three locations, Mr. Whittaker said. Staging for the new overpass bridges will take several weeks at each site. Staging at Greenleaf Street will be in part of the Jewel Food Store parking lot and will likely take five months. The Dempster Street staging, about a six-month project, will be along Sherman Place, east of the CTA right-of-way. The south 36 feet of eastbound Grove Street will be used for that staging area for about six months.

The CTA has contracted with Kiewit to perform the work. Although the contract allows 640 working days for construction, Mr. Whittaker said the company expects to have the projected completed sooner than that, perhaps by late fall of 2012.