A poll in Stern magazine on Wednesday showed 60 percent of Germans favour limits on the Autobahnen network to protect the environment.

Environmentalists want a blanket limit of 120 kph (75 mph) in an attempt to reduce carbon dioxide (CO2) emissions, but the transport ministry has rejected the proposals.

Carmakers, such as BMW, Porsche or the Mercedes unit of DaimlerChrysler, say speed-limit free roads lead to innovation and better, safer cars.

Together with European divisions of Ford and GM, German carmakers employ millions of workers.

Ralph Alex, deputy editor of Auto, Motor und Sport magazine, said the need to engineer cars for high-speed driving meant they were more expensive to build but that they had better brakes and safety features than French or Japanese rivals.

"If you buy an expensive top-class car in Germany then you know that it is capable of driving at 250 kilometres per hour (155 mph)," Alex said. "And that's a good argument for premium-priced German cars across the world."

Alex said around 80 percent of Germany's highways had some form of speed limit and the average speed nationwide was 114 kph (71 mph), with congestion and roadworks making rapid progress difficult.

"In terms of the environment it makes no sense to limit the remaining 20 percent," Alex said. "Mother nature is not going to notice the difference and road deaths are unlikely to fall."