CHICAGO (CBS) — Mayor Rahm Emanuel is defending the Chicago Transit Authority’s plans to shut down the Dan Ryan branch of the Red Line for several months next year while the ‘L’ is rehabilitated.

As WBBM Newsradio Political Editor Craig Dellimore reports, Mayor Emanuel says the choice for CTA officials was fairly clear. They could rehabilitate the south branch of the line over four years and close stations on the weekends – when normal ridership is high – or, he says, they could choose the work in five months and provide alternative, free or discounted bus service.

LISTEN: WBBM Newsradio Political Editor Craig Dellimore reports

There are benefits to the five-month shutdown option, Emanuel said.

“In the savings of the $75 million, the people on the South Side will get free — free — shuttle service. People that don’t use the shuttle service, but will be taking buses, will get a discounted rate by about 50 cents a ride,” he said.

After the work is over, Emanuel said, riders will shave about 20 minutes off their commute times because slow zones will be gone.

The city announced on Monday that the south branch of the Red Line will close for five months next spring for the $425 rehabilitation project.

CBS 2’s Jim Williams rode the south Red Line on Tuesday to see just how severe the slow zones on the line could be. At one point the train was forced to creep along so slowly, CTA Chief Infrastructure Officer Chris Bushell said a bicyclist could move faster.

He compared CTA slow zones to a street with potholes.

“Except lots of potholes; so many potholes, so many defects in your street, that you can’t even get to your house; or if get to it, you get to it very slowly,” Bushell said.

The tracks are worn out, and the ballast stones that keep the tracks and ties stable are also in bad shape.

The rails have also significantly deteriorated, because they are the same rails installed when the Dan Ryan branch opened in 1969.