It’s another idea from the “green” crowd that sounds great when you talk about it, but which proves to be a bust in the marketplace. This time we’re talking about bike-sharing programs that have cropped up in cities around the country. Many are, at least in part, publicly funded. Which means, of course, that when reality hits, the hard-earned tax dollars are gone — and the bikes are sitting in the corner. From the Wall Street Journal:

Bike-sharing programs are spreading across the U.S., with more than 21,000 shared bikes in at least 36 urban areas from Boston to Fort Worth, Texas, to Denver, up from just six programs in 2010, according to researchers.

More than half of the programs have stumbled, according to a tally by The Wall Street Journal. Several had to delay their launch because of technical snafus or trouble securing funding from government or the private sector.

In several other places, supplier woes have thwarted plans to add bikes and stations needed to rev up rider revenue. And some bike-share systems are scrambling for money needed to keep them rolling or help them expand.

“The only macro trend is chaos,” says Ryan Rzepecki, chief executive of Social Bicycles Inc., of New York, which supplies bikes and other equipment to the 16-month-old program in Buffalo. “The industry is kind of a mess.”

Despite this economic reality, some cities continue to live in dreamland — which is a very comfy place to be when you’re spending OTHER people’s money.

Bike Chattanooga was billed as a new mass transit system in a car-centric city once known for its industrial pollution. Residents and tourists visiting the Tennessee Aquarium and Chattanooga Choo Choo Hotel can avoid using cars, buses or free electric-powered shuttles with a rented bike.

Chattanooga Mayor Andy Berke says the 300-bike program boosts downtown businesses, the city’s tourism industry and Chattanooga’s outdoorsy brand. “People enjoy it and love it,” he says. “I understand there are things in the community which we need that don’t make money.”

So far, though, only about 540 riders have signed up for $75-a-year memberships, about one-tenth of the initial target, says Philip Pugliese, one of the city officials who oversees Bike Chattanooga.

And so it goes.