For decades, the world's been wondering what comes next--after the era of gasoline, that is.

And since 1998, a global convocation of scientists, politicians, transportation companies and journalists have gathered somewhere in the world for the Challenge Bibendum, a sort of green-car congress that poses the question, "what does sustainable mobility mean?"

It's a fair question. By some estimates, there could be an additional 700 million vehicles on the world's roads in the next decade, which organizers imply is clearly not sustainable. That's triggered the search for new ways to move people around, and resulted in the Bibendum, where anything that's an alternative or an improvement on today's petroleum-fueled, internal-combustion-powered vehicles is worthy of inclusion.

Judging from the attendees at this year's Bibendum--which was christened to coincide with the 100th anniversary of Michelin, the company which coordinates the semi-annual event--sustainable mobility can mean anything from an ethanol-fueled commercial vehicle sold under generous Brazilian tax credits and loan programs, to a simple bicycle fitted with an electric battery that helps less able riders make it to their destination.

This year's Challenge Bibendum is the first since 2007, since the financial crisis swept away a third of the global transportation market's sales. Dipping a toe back in the water, Michelin's staged the 2010 Bibendum in Rio De Janeiro, Brazil, a past host of U.N. global climate change conferences and the named host of the 2016 Summer Olympic Games.

Rio is the first South American city to host the challenge, and it has a compelling hook. Brazil is ground zero for the biofuels industry, with nearly 100 percent of all vehicles sold in Brazil equipped to run on ethanol.

And, in case you've never been, it's a gloriously shabby city. In summer it's less rainy than this week's downpours and cool temperatures, and that's when Rio shows off its staggering natural beauty, from beach-built Carioca bodies, to its gorgeous harbor capped by Sugarloaf Mountain, or the Christ the Redeemer statue that checkmates the hunchback mountain that has the city's back, Corcovado.

The rain's blotted all that out this week, and nearly drowned out the green-car competition that puts the "Challenge" in the Bibendum. Almost 80 vehicles will compete in a rally around the city and several benchmarking tests, and a winner in each of three categories is named (cars, trucks and buses, and urban vehicles). The winners are the vehicles that succeed best at lowering emissions and environmental impacts of all kinds, from carbon dioxide to noise. But while the weather's taken a toll, it's also focused attention on the panel discussions on the future of green cars and the environmental thinking that will shape the next iterations of sustainable mobility.

High Gear Media's reporting from Rio de Janeiro today and tomorrow. You can look back at coverage from TheCarConnection of prior Challenges Bibendum by following the links below. And for the 2010 Rio Challenge, you can bookmark this page to follow our updates here on GreenCarReports.com, and follow links to stories from our other sites, including AllCarsElectric.com and MotorAuthority.com.

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Fiat FCC II Concept, 2010 Michelin Challenge Bibendum

Fiat FCC II Concept, 2010 Michelin Challenge Bibendum

2010 Challenge Bibendum, Rio de Janeiro

The Next Big Range Extender in Electric Cars? Tires -- AllCarsElectric.com

2010 Michelin Challenge Bibendum: Facts and Figures -- GreenCarReports.com

Michelin Challenge Bibendum: 7 Cars from a Sustainable Future -- GreenCarReports.com

Recycling Your Car? Try Recycling a Whole Airport -- GreenCarReports.com

2010 Michelin Bibendum Challenge: Kids Predict the Future of Cars -- TheCarConnection.com

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Challenges Bibendum

1998: Clermont-Ferrand

2000: Clermont-Ferrand

2001: California

2002: Heidelberg - Strasbourg - Paris (Germany and France)

2003: Sonoma, California

2004: Shanghai (China)

2005: Kyoto and Nagoya (Japan)

2006: Paris (France)

2007: Shanghai (China)