CTA purple line viaducts

Work continues on the CTA Purple Line viaduct on Dempster Street in Evanston. (Jose M. Osorio / June 21, 2012)

Two century-old train viaducts in Evanston will be replaced this weekend in a move that officials say will increase safety and speed travel times along the CTA Purple Line.

The 400,000-pound steel replacement bridges were assembled off-site and loaded onto hydraulic lifts in preparation for installation. Train service between Howard and Davis streets will be suspended at 8:30 p.m. Friday. It’s expected to be restored by 4:30 a.m. Monday — in time for rush hour.

The weekend work is scheduled around the clock at Dempster and Grove streets to demolish the existing concrete viaducts, slowly move the steel bridges into place with a crane, and rebuild the tracks.

The $10.3 million project also includes a third new CTA viaduct at Greenleaf Street that was installed earlier this month.

Replacement of the crumbling bridges has been talked about for more than 15 years, officials said at a Thursday press conference. CTA President Forrest Claypool said the Evanston stretch of the Purple Line has been “one of the few places where trains actually had to roll to a stop in many instances.”

“These viaducts are essential not just to the economic lifeblood of this community, but there’s a strong safety consideration as well,” said State Sen. Jeff Schoenberg, D-Evanston, referring to the crumbling concrete bridges and diminished train speeds.

Schoenberg and Claypool were hailed by city leaders as instrumental in acquiring funds and realizing the project.

Grove and Dempster streets, around the viaducts, will be closed to traffic beginning at 7 a.m. Friday. Grove is expected to reopen by 5 p.m. Monday, while Dempster is scheduled to reopen at 5 p.m. Tuesday.