CHICAGO (CBS) — Chicago aldermen have approved the creation of a new TIF district to help secure $1.1 billion in federal funding for projects to modernize the Red and Purple Lines on the North Side.

At a special City Council meeting, the aldermen discussed and approved a series of ordinances to create a new Transit TIF District that would run for about six miles along the Red and Purple Lines, and in one-half mile on either side of the tracks.

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TIF districts raise money by effectively freezing property taxes in the district for 23 years, and funneling any increases in taxes from rising property tax values into a special fund used for specific purposes. The transit TIF would last for 35 years, and unlike normal TIF districts, schools within the district would continue to get their normal portion of increased tax revenue.

City officials feared a new presidential administration might delay or decrease the $1.1 billion in federal matching money the Obama administration has offered for the transit project, and had to act by Wednesday to commit to $622 million in local funding to guarantee that federal grant.

The projects to be funded would include replacing Red Line tracks from Lawrence to Bryn Mawr, creating a controversial flyover to separate the Red and Purple Lines from the Brown Line where they intersect north of the Belmont station, and improving signals from Belmont to Howard.

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Opponents of the TIF plan fear it will divert money away from other needs in the district. They also worried the project will increase property values, and therefore tax bills.

Supporters argued the Red and Purple Line improvements are essential, because of the aging infrastructure.

Ald. Harry Osterman (50th) said, with no possibility of state lawmakers agreeing on a capital construction bill to fund the CTA project, it was up to the City Council to create the new transit TIF district to retain the federal grants.

“This is not something that was done quickly. This is something that’s done methodically, working in tandem with the U.S. Department of Transportation, the RTA to have this project to where it is today; but the reality is is that we’re here out of necessity,” he said.

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The CTA also has approved $468 million for the project, which will total about $2.1 billion.