Hold onto your helmets, city dwellers. It’s the summer of bike sharing.

Around the world, cycle-hire operators are rolling out bicycles that were tucked away for the cold and rainy months. Hundreds of new bikes and docking stations will join existing fleets, while many more cities, from Kailua to Tel Aviv to the Big Apple are joining the bike-sharing wave for the first time.

The idea is simple: Charge a nominal fee to give people all the benefits of cycling without the hassle of bike ownership. It’s an old idea, but the concept of a bicycle fleet for shared use has undergone a very modern makeover in recent years.

Today’s bikes are often equipped with GPS devices for tracking. Free and coin-deposit systems have given way to solar-powered, computerized docking stations designed to deter theft and afford easy installation. Users often can reserve a bicycle with a few taps on a smart phone, unlock a bike with the swipe of a smart card that links up with the local metro, and even track calories burned while pedaling.

Pedal to the Metal

The number of bike-sharing services in 10 European countries, including Austria, Belgium, Czech Republic, France, Germany, Italy, Poland, Spain, Sweden, and the United Kingdom, has leapt to about 400, up from “only a few” a decade ago. That’s according to Janett Buettner, executive director of Berlin-based research and development firm Choice GmbH and the coordinator of a forthcoming report on strategies for successful bike-sharing programs in European cities.

The report itself, conducted over three years and supported by 15 public and private organizations in ten countries, is a sign of the momentum propelling a new generation of bike-sharing systems. Of course, for evidence of their popularity, just consider London’s gift to the recently wed royal couple: a specially designed tandem version of the bicycles used in the city’s Barclays Cycle Hire scheme.

The EU’s bike-share boom was triggered by the launch of a pair of large, popular schemes in Paris and Barcelona in 2007, Buettner said in an email. But in the past few years, bike-share programs have gained ground beyond Europe—in Mexico, Brazil, Canada, South Korea, Taiwan, Australia, and other countries. The city of Tel Aviv, Israel, has invested $25 million for the new Tel-O-Fun program, which launched last month with 40 stations and 450 subscribers.

Even the United States has seen bike-sharing programs sprout up in cities and college campuses in a trend that Buettner called “remarkable,” due to the country’s limited popular cycling culture.

Kailua, Hawaii, is one of the latest American cities to join the trend. Launched in early May and funded by tobacco settlement money through the state health department, the municipality’s $100,000 pilot program has only a dozen bikes at two stations, although there are plans to expand if the pilot proves successful. Similar to other programs, annual membership is $50, and a one-day pass is $5. That buys access for up to 30 minutes with no additional charges. After 30 minutes, members pay $2.50 per half-hour.

On another U.S. island—Manhattan—Mayor Michael Bloomberg’s administration has called for proposals for a cycle-hire scheme that would begin this summer with 30 test stations before expanding to 10,000 bicycles at 500 stations by April 2012. The administration expects the winning bidder to privately finance the system and share revenues from user fees and sponsorships with the city.

In Chinese cities, where once the bike was king, the recent rise of bike sharing fits into the country’s larger trend of growing demand for mobility, said Susan Shaheen of the Transportation Sustainability Research Center at the University of California Berkeley.

In fact, the Public Bicycle System in one of China’s wealthiest cities, Hangzhou, has surpassed Paris’ Velib as the world’s largest bike-share program, with 60,600 low-cost, low-tech bikes and more than 2,400 stations spaced out about every 200 meters, Shaheen said. Since Hangzhou opened the floodgates in 2008, more than a dozen other cities in China have launched cycle-hire schemes. Uniquely, China provides insurance if an accident happens during a trip. “No other place has bundled that in,” said Shaheen.

Speed Bumps

Yet bike sharing is not without roadblocks. A successful program must strike a delicate balance of interests that sometimes come into conflict. “The operator wants to earn money with the scheme, the mayor wants visibility and low costs, the user wants easy and cheap usage,” said Buettner.

Just getting the real estate for docking stations can be politically challenging. In New York City, community board members are complaining that the stations may take away parking spots or eat up space on already crowded sidewalks.

As for existing bike-share schemes, there’s no guarantee the services will stick around long term. In the year since its launch, Melbourne Bike Share in Australia has sputtered. The number of monthly trips falls about 2,000 short of the 15,000 trips needed for the program to break even, possibly due to compulsory helmet laws (which can discourage spontaneous and casual use), a wet summer, and inadequate bike lanes.

After all, bike-sharing schemes address only some of the obstacles to urban cycling. On their own, they don’t make a city bike-friendly. That’s part of why bike-sharing pioneer Paris isn’t coasting on the success of its Velib program. Rather, the City of Light aims to add more than 160 miles of dedicated bike lanes to its 273-mile network by 2014 as part of a comprehensive four-year cycle plan unveiled in 2010.

In Canada, meanwhile, controversy has erupted over a decision last month by the Montreal government to provide $108 million in loans and guarantees for city-owned Public Bike System Company, which has made bike sharing a Canadian export. The not-for-profit company’s BIXI bikes and docking system were first launched in Montreal in 2009. The equipment is now used in London, Toronto, Ottawa, Minneapolis, Washington, D.C., and elsewhere around the globe, often with operators such as Alta Bicycle Share running the programs. BIXI is a heavyweight in the new world of city bike-sharing systems and its revenue from international sales is on the rise. Yet the original Montreal program loses $7 million per year.

Behind the Boom

In the big picture, however, bike share schemes are relatively easy to implement and cheap compared to other transportation projects, said Buettner. And, she said, “at the end of the day they support the green image of a city.”

For those reasons, the real impetus for a new cycle hire program often comes down to politics, she said. Behind any given launch, one will often find a mayor or party looking for a topic that will cast them in a positive light.