Germany’s speed limit-exempt autobahn system faces a new challenge in the form of a recently elected Green party which plans to cap speeds to reduce vehicle emissions.

A collation of the Greens and the Social Democrats took power in the German state of Baden-Wuerttemberg following the March 27 election.

Baden-Wuerttemberg is the country’s third-largest state and its capital, Stuttgart, is home to Mercedes-Benz and Porsche.

The Social Democrats want to implement a 130km/h speed limit on the state’s autobahns, while Green Premier Winfried Kretschmann said he was in favour of 120km/h limits.

“Traffic in Baden-Wuerttemberg contributes about 30 percent to [the state’s total] CO₂ emissions,” Mr Kretschmann said.

“It’s clear that the transportation sector has to make a contribution of its own to reduce this gas that’s harmful to the environment.”

Opponents of the new government’s proposal have highlighted the fact that only a tiny proportion (estimates suggest around two percent) of the nation’s driving takes place on unrestricted autobahns, and subsequently the CO₂ savings will be minimal.

Germany’s autobahn highway network stretches 12,200km and about 45 percent of that is unlimited. It has an advisory speed limit of 130km/h.

Porsche has not commented on the outcome of the election, but Daimler CEO Dieter Zetsche said high-speed autobahns were important to both Germany and the development of Mercedes-Benz vehicles.

Meanwhile, the Department of Transport in Texas, US, is driving in the other direction, with the House of Representatives recently approving a bill to raise speed limits to as high as 85mph (137km/h).

Texas already has 840km of highway with 80mph (129km/h) speed limits, so the jump to 85mph isn’t quite as dramatic as the German proposal.

It won’t be as simple as putting up new speed signs, however. The Department of Transport will have to conduct a series of traffic and engineering studies in order to get approval to increase the speed limit.

Just like in Germany, the plan has its detractors.

Southwestern Insurance Information Service spokesman, Jerry Johns, told the Dallas Morning News he believed 85mph was just too fast.

“The two things that kill most people on our highways are speed and alcohol. Increasing it to 85 … will have a dramatic impact on the death and injury rate on those highways where it’s implemented,” Mr Johns said.

“Eighty-five miles per hour is simply too fast to drive even on a flat road. Any little hitch can cause an accident at that speed. There is still traffic on those roads, and to drive 85mph is simply ludicrous.”