Commuting around and through downtown is going to get rougher this summer: The CTA is planning to tear up and replace tracks on more than half of the Loop.

On weekends starting April 20, the CTA will do work on sections of track mostly on the south and west sides of the Loop, as well as the junctions at its northwest and southeast corners. A section of Brown Line track between the Merchandise Mart and Chicago Avenue stations will be redone, as well.

As a result, stations on the south and west sides of the Loop — that’s the Harold Washington Library, LaSalle/Van Buren, Quincy and Washington/Wells stops — will be shut down for a good number of weekends between now and this fall.

Train traffic throughout the entire system will be affected, as well, including the Green Line, which doesn’t run along those legs of track. That’s because trains that would normally go around the entire Loop will be turning around in the middle of the tracks on the east and north sides of the Loop.

Reconstruction on the junctions will also mean squeezing every elevated train line through a single-track point, especially at the Loop’s northwest corner, which is one of the busiest rail junctions in the U.S.

The construction won’t affect trains during the work week, for the most part. The CTA says they’ll limit construction to weekends (with occasional overnight work during the week) and they’ll hold off during the Taste of Chicago, Lollapalooza, the Air and Water Show, the Chicago Marathon, Blues and Jazz Fests.

The CTA will be replacing everything between the platforms, essentially, including metal tracks, the electrified third rail, wooden railroad ties and walkways at track level. Much of the track that’s being replaced was first installed in the 1980s and is at the end of its useful life, meaning that while it might not be crumbling, it generally isn’t cost-effective to maintain.

Brian Steele, a spokesman with the CTA, said that the parts of the system that will get the most work are less traveled, in general.

“The west and south legs of the Loop elevated, those stations have a much lower ridership than the ones on the north and east side,” Steele said. “The State and Lake corridors have a lot more activity than the Wells and Van Buren corridors.”

The Loop’s north and west sides were already rebuilt in 2008. This year’s construction is being paid for with a $33.8 million grant from the state of Illinois, and is expected to be finished by next fall.