Germany, home of the high-speed autobahn, is perhaps one of the few countries that has had as intense a love affair with the automobile as the U.S. But in an effort to go green, the country's second-largest city is studying ways to eliminate cars by 2034.
The northern city of Hamburg has laid out an initial concept, named the Green Network Plan, that would expand public transportation and add more routes for pedestrians and bicyclists. The most controversial aspect of the plan calls for a steady phase-out of automobiles in the center of the city over the next two decades.
And Hamburg might not be alone. The idea of banning, or at least reducing, the use of automobiles in city centers has become an increasingly hot topic among urban planners, especially in Europe and other industrialized countries dealing with issues as diverse as congestion and smog.
According to a new study by IHS Automotive and Groupe Futuribles, congestion will cause annual auto sales to be trimmed by 30 million vehicles annually by 2035.
(Read more: 'Global gridlock': Study says congestion to jam car sales)
"Other cities, including London, have green rings, but the green network will be unique in covering an area from the outskirts to the city center," Hamburg city spokeswoman Angelika Fritsch told The Guardian newspaper. "In 15 to 20 years, you'll be able to explore the city exclusively on bike and foot."
(Read more: More city dwellers steer clear of owning cars)
There are already a handful of car-free communities around the world, but they're typically small and often focused on tourists seeking a quaint throwback in time. Examples include Michigan's Mackinac Island or Sark island off the English Channel coast of the U.K.; perhaps the largest is Venice, which simply has no way to open up roads linking its network of small islands.
But a number of major cities, including the likes of Paris, London and even New York, have been exploring ways to reduce the number of vehicles on their streets, if not to ban vehicles outright.
London introduced a much-debated congestion charge for vehicles driving into the center of the city in 2003. The program had a dual purpose—reducing commuter traffic while also raising new funds to support the city's expansive mass transit system. The charge is 10 British pounds per day.
(More from The Detroit Bureau: Performance, not mileage, the big story in Detroit)
Several other cities have adopted a similar approach, though former New York Mayor Michael Bloomberg's bid to put one in place in crowded Manhattan was blocked by state lawmakers. Nonetheless, changes have been made in several parts of Manhattan, including a stretch near the theater district, to create pedestrian zones to absorb the mass of tourists.
Many urban planners accuse automobiles of killing street life, with roadways often dividing once-connected neighborhoods, and creating endemic air and noise pollution. They also cite them as as being a major factor in pedestrian deaths and injuries.
Lord Richard Rogers, a British architect and long-time advisor on urban issues, suggested last year that London should become "a people space rather than the car space it currently is."
But the website CarFree.com cautions that simply banning automobiles won't be a quick fix. "The challenge is to remove cars and trucks from cities while at the same time improving mobility and reducing its total costs," it says.
Urban planners have an array of alternatives they can draw from as they try to make cities at least less dependent upon automobiles. They include congestion charges and more limited car-free zones, such as the popular Third Street Promenade in Santa Monica, Calif. Several British communities are exploring the creation of similar restricted spaces.
(More from The Detroit Bureau: Outgoing GM CEO tells the backstory on automaker's bailout)
Other cities, such as Paris, have raised the idea of banning some, but not all, automobiles. One approach would put a restriction on the use of vehicles powered by internal combustion engines, while electric- or hydrogen-powered automobiles would still have free rein. In some instances, such vehicles are already exempt from urban congestion charges.
The auto industry sees restrictions as increasingly unavoidable and is trying to adapt by, among other things, having more battery-car offerings. Some of the latest plug-in hybrid models, such as the new Porsche Panamera Plug-In, allow drivers to stick to gas power on highways coming into a city then switch solely to electric propulsion to gain access and avoid toll charges.
While pressure to push cars out of urban centers has become most intensive in older European and some American cities, urban planners in some emerging markets are also beginning to consider the challenges posed by the automobile.
(More from The Detroit Bureau: Competition heats up for entry-level luxe)
Beijing, Shanghai and some other Chinese cities, for example, have been enacting rules to reduce the number of new vehicles that can be sold and registered. And with some of those cities already reaching gridlock, it's a question of whether more radical solutions might follow.
How the public reacts remains to be seen. A number of efforts to create pedestrian malls in the U.S. have failed, and motorists—and the businesses that support them—make up a powerful lobbying force. The concept of carless cities is likely to generate a loud global debate in the years ahead.
—By CNBC Contributor Paul A. Eisenstein. Follow him on Twitter @DetroitBureau or at thedetroitbureau.com. With contributions from CNBC's Phil LeBeau. Follow him on Twitter @LeBeauCarNews.