A civic group is proposing that parts of 20 Chicago streets, including the city’s vaunted Magnificent Mile, be turned into “car-free” zones — which could mean complete bans on all trafffic to the more modest dead-ending of a street into a plaza.

Even Chicago’s North Michigan Avenue could do with less cars, and should be examined for everything from the insertion of more plaza space, to allowing only buses, to banning all vehicles from Oak Street to the Chicago River, according to leaders of the Active Transportation Alliance.

“Nearly a quarter of Chicago’s land mass falls within a public right of way, but most of that space is dominated by cars,’’ the Active Transportation Alliance noted in releasing its car-free zone proposal Wednesday.

“Car-free streets and zones can make communities more attractive places to live and shop, generate more biking and walking and thus improve mobility and health, and reduce traffic crashes,’’ the Alliance said.

“Let’s give Chicagoans more car-free zones to walk, bike, shop, socialize or just relax.’’

The Alliance has been a big supporter of Chicago’s bike lanes, its Divvy bike sharing-program and its Ashland Bus Rapid Transit plan to run a dedicated bus lane down the center of Ashland Avenue for 16 miles. It endorses Mayor Rahm Emanuel’s quiet revolution to create more “Complete Streets” that ensure pedestrians, bicyclists, transit users and motorists can all travel safely on public rights of way.

A so-called car-free zone can take many forms besides merely turning a street into a full-time car-free mall, said Ron Burke, Active Transportation Alliance executive director.

A street can be dead-ended and turned into a pedestrian plaza. A car lane can be converted to a bike lane and plaza. Or a street can be shut down seasonally, on weekends or on evenings for special events.

Burke cited as examples New York City’s lively Times Square and Chicago’s Navy Pier. In contrast, he said, the city’s State Street mall was a flop because it was “badly designed” and asked pedestrians to cross a wide street while dodging fast-moving buses. The mall closed off State Street downtown to the driving public from 1979 until 1996, when it was reversed.

More successful, Burke said, is Denver’s 16th Street Mall, which uses center-running buses that travel more slowly on a narrow street.

On the Mag Mile, Burke said, cars occupy most of the right of way but only move a small percent of people on that street. Said Burke: “The slog of vehicles divides the two sides of this shopping mecca where there are so many people on foot. For these reasons, it’s a good candidate for further analysis.”

“I’m looking out the window right now and everything is flowing pretty good,’’ responded John Chikow, president of The Magnificent Mile Association. “I don’t know what they are talking about. I’d love them to come to [our] monthly meeting and share their thoughts.’’

Downtown Ald. Brendan Reilly (42nd) argued it would be “irresponsible” to permanently close Michigan Avenue to private vehicles because of the “major traffic impact” it would have for blocks.

“I don’t think turning Michigan Avenue into a pedestrian mall makes sense. We saw that experiment fail on State Street. I’m not sure why we’d want to replicate that,’’ Reilly said.

“I’ve learned during my time as alderman that when you block off one street, it shifts all of that volume onto neighboring streets. Michigan Avenue is a major arterial street with tens of thousands of cars traveling on it every day. The impact on east-west streets would be significant.’’

Burke said the alliance’s list is merely a starting point for conversation and “we’re not saying all 20 of these streets would work. We’re asking the city and aldermen and city leaders to evaluate these sites to see what the potential is.’’

Proposals include:
◆ Converting at least one lane of traffic on Clark or Dearborn Street into a protected bike lane and installing landscaped seating next to it, from River North to the South Loop.
◆ Making all of Monroe Street, between Michigan Avenue and Lake Shore Drive, car-free. Parkland would be inserted and underpasses would “replace difficult crossings at Michigan Avenue and Lake Shore Drive.’’
◆ Converting all of Broadway, from Diversey to Belmont, into a “car-free greenway” with landscaping, seating, and restaurant patio space. Cars could divert to Clark and Halsted.
◆ Closing Humboldt Drive and/or Luis Munoz Marin Drive in Humboldt Park to car traffic in the summer to expand park space.

Other areas targeted for “car-free’’ zones but with less specific ideas detailed in the group’s press release include:
◆ Segments of Rush Street and Oak Street in the Gold Coast.
◆ One or more streets near Wrigley Field.
◆ Segments of Clark in Andersonville; Webster Avenue in Lincoln Park; Milwaukee Avenue in Wicker Park.
◆ Bryn Mawr between Broadway and Sheridan Road; Simmonds Drive between Lawrence and Foster.
◆ Taylor Street between Racine and Ashland; segments of 26th Street in Little Village.
◆ Segments of E. 53rd in Hyde Park; 47th Street in Bronzeville; 18th Street in Pilsen; Ellsworth and/or Payne Drives in Washington Park.