Chicago is one of six cities where Lyft is offering free rides on Earth Day, which is being celebrated for the 50th year on Monday.

The promotion comes after a controversial deal approved by the Chicago City Council made Lyft the exclusive operator of the city’s Divvy bike-rental service.

Lyft’s Earth Day offer isn’t for its ride-hailing car service, but rather is a way to encourage the “carbon-free” use of bicycles in Lyft’s bike-share networks across the country, according to a blog post on the company website.

In Chicago, that means a free day of unlimited Divvy rides with an “Explorer Pass,” good for three free hours at a time. After three hours, the bike must be docked; Divvy has 580 in the Chicago area.

The Explorer pass, which usually costs $15, can be downloaded with the Divvy app by entering promo code EARTHDAY19.

New York, Washington, D.C., Minneapolis, Portland, Oregon and Columbus, Ohio, are the other cities where the free rides are being offered.

The first Earth Day, in 1970, was intended to highlight a range of environmental concerns. Today, the goal is to address climate change and the use of fossil fuels by changing behavior as well as public policy.

Lyft’s Earth Day campaign was announced Friday, a little more than a week after the City Council OK’d a deal for the ride-hailing company to become the exclusive provider of the city’s bike-share services.

The nine-year deal calls for Divvy to go citywide by 2021 with a total of 16,500 bikes docked at 800 stations.

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