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.



Hamburg, Germany street scene Reza Estakhrian | The Image Bank | Getty Images

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.