Earth Day is coming around the bend, and cities are timing their new green initiatives to coincide with the public’s heightened eco-consciousness. Here’s one we’re partial to: In Denver, Mayor John Hickenlooper and city leaders are using the occasion to launch their 500-bicycle, 50-station bike-share system. It will be the largest bike-share system in the U.S. until Minneapolis and Boston roll theirs out later this spring.

Denver will launch its bike-share system this week with 500 bicycles at 50 stations, aiming to expand to 1,100 bikes in 2011.

While Minneapolis and Boston selected the company behind Montreal’s Bixi to run their bike-share systems, Denver went with B-cycle, a joint venture between Trek Bicycles, health insurer Humana, and PR firm Crispin, Porter + Bogusky. B-cycle had a demo station set up at Pier 84 on the Hudson River Greenway yesterday, where I had the chance to talk to company president Bob Burns about how the system works.

In Denver, B-cycle will be financed by ads and user subscriptions, with annual memberships priced at $65. Members get RFID cards that they can use to to check out bicycles at individual docks with a wave of the hand. The first 30 minutes of each ride are free, with each additional hour priced at one dollar.

The stations can run on solar or A/C power. Denver has chosen to place their kiosks in plazas and other pedestrian spaces, not in parking lanes like they do in Paris.

One of the interesting features that distinguishes B-cycle is its tracking system. Each bike is equipped with a GPS unit, so users can access their member profiles online and see where they biked, how far they rode, and how many calories they burned. The cumulative GPS data from the entire system should also prove to be a valuable resource for transportation planners. "It gives cities a lot of information on where cyclists are going and which routes are being used," said Burns. "They can make more intelligent decisions about where to invest in infrastructure."

Buoyed by Ray LaHood’s recent statements of support for bicycle infrastructure, Burns was appropriately bullish, for a bike-share exec, on the future of bike-share in American cities. "Once people see it can happen and that it can work, and people in those cities appreciate it," he said, "we think it’s gonna explode."