CLEARWATER — They shuttle people over mountain terrain in Bolivia, across the River Thames in London and between villages in Hong Kong.Aerial cable cars, or gondolas, have made their mark internationally as mass transit systems to alleviate traffic problems and give tourists a view, but the trend has been slower in the United States.Only two American cities have gondola commuter systems — New York's Roosevelt Island Tramway and the Portland Aerial Tram. But as metropolitan areas battle traffic congestion that follows urban development and population growth, a growing number are looking to the skies for solutions. And Clearwater may be one of them. St. Petersburg developer Darryl LeClair in the last few months has spoken to various local and regional officials about a potential gondola system to connect downtown with Clearwater Beach. Although representatives of his real estate company, Echelon, declined to comment on the idea to the Times, Clearwater City Council member Doreen Hock-DiPolito said it's a concept — while not yet even on paper — that should be considered.Across the country, serious proposals are being mulled in at least a dozen major cities. In Virginia, the Arlington County Board on Thursday okayed a feasibility study to explore a gondola system over the Potomac River connecting Georgetown and Rosslyn and easing traffic on the Key Bridge.A software company in Cleveland has been working for several years on a proposal for a 14-station aerial lift to connect the waterfront to the city core. Michael McDaniel, a designer who proposed an urban gondola for Austin, Texas, said interest is rising because the technology is cheaper than light rail and subway systems and more efficient than buses for growing communities. But buy-in might be the barrier so far."It comes down to politics and familiarity," McDaniel said. "No one ever wants to be perceived as having a boondoggle on their hands, gambling with taxpayer money. That's the worst position to be in. … it's a high-risk situation, but the first city to be brave enough to do it, more will follow."Gondolas typically run between 12 and 15 mph, pack usually eight to 10 people per cabin, and have a cabin roughly every 200 feet. They run continuously in a circulating system, slowing (but never stopping) at stations where riders never have to wait long for cars to arrive. The systems in New York and Portland differ as aerial tramway systems, with two large cabins that carry more than 100 people each and shuttle back and forth in both directions. Gondolas, which are popular in South America and Europe, can run in winds up to 50 mph but typically shut down during lightning or high intensity gusts, said Mike Deiparine, senior project manager for SCJ Alliance, which worked on the Cleveland gondola proposal."Often passenger tolerance for wind operation is more restrictive than the equipment," he said. "A tropical storm or hurricane is another matter entirely, but I wouldn't want to be on an Intracoastal bridge during one of those either."Because they are made up of boarding stations, cable cars and cables, they are typically less expensive than most other transportation options, running about $3 million to $12 million a mile depending on the architecture, Deiparine said. Light rail systems can average $36 million a mile. Mark Bee, president of the U.S. arm of Doppelmayr, the world's leading developer of aerial tramway systems, said gondolas work best in high density geographies or in cities with a need to transport people over mountains and waterways. Bee said other countries may have been quicker to adopt gondolas because the United States has stronger private property laws to consider. He said gondolas across waterways are easier because they go over public right of ways. Bee said his company is in "active dialogue" with 15 to 20 gondola projects in the United States and he expects three to four of those to happen in the next decade.However the time lines for gondolas can be long — it was 10 years from concept to completion in Portland, and permitting and fundraising can be tricky.Dan Levy, the creator of the East River Skyway proposal, which aims build a gondola system over the river connecting Brooklyn and Manhattan, said population growth and urban density is driving this technology. His 2-mile project is estimated to cost between $75 million and $150 million to build and would carry 5,000 riders an hour in both directions on 40 cabins. His project, like Clearwater's potential system, depends on private investment and public buy-in. With just one subway line connecting the north side of Brooklyn to Manhattan, and an ever-growing population, Levy said cutting congestion on roads and bridges is the most logical option."The need is undeniable and very recognizable," he said. "There's not a lot of ways you can solve that problem."Contact Tracey McManus at [email protected] or (727) 445-4151. Follow @TroMcManus.