Protesters supporting janitors who want higher pay and more sick time took to the streets Thursday, blocking downtown roads at the peak of the morning rush hour and causing massive traffic jams on Interstate 94 and I-35W.

Marchers took over 12th and 11th streets and the area of 3rd Avenue to 5th Avenue S., Minneapolis police spokesman John Elder confirmed. At the 5th Avenue exit off I-35W, some protesters played music and carried banners that called for a raise in the minimum wage to $15 an hour.

Traffic heading into downtown was at a standstill for nearly an hour, and the State Patrol shut down major entry points. Exits from northbound I-35W to 5th Avenue and westbound I-94 to 5th Avenue were closed around 8:15 a.m. They reopened 30 minutes later as marchers made their way along city streets to the area of 8th Street and Nicollet Mall, according to scanner reports.

Backups as long as 3 miles were reported on northbound I-35W, Minnesota Department of Transportation cameras showed. Highway traffic normalized around 9 a.m.

Still, the protests angered some commuters. "Making me late for work isn't going to make me feel sympathetic to your cause," a disgruntled commuter tweeted.

Twin Cities janitors staged a one-day strike Wednesday in an effort to improve working conditions.

Ben Farniok is a University of Minnesota student on assignment for the Star Tribune. • 612-673-7768