Carpool lanes have been an accepted part of the landscape in California for more than 40 years now.
But they're less well-known in Europe, where bus lanes have taken priority instead – largely due to pervasive and well-accepted mass transit systems.
But now Germany is planning to test the concept of "eco lanes," restricted to not only vehicles with multiple passengers but also those with the lowest emissions.
As laid out in Stuttgarter-Zeitung (in German), the state of Baden-Wuerttemberg plans to conduct a feasibility study on of what it calls “Umweltstreifen” (eco lanes).
California has always granted carpool-lane access to zero-emission vehicles; certain hybrid vehicles were also allowed from 2005 to 2011, but the state has now switched that privilege to plug-in hybrids.
In the German test, however, the lanes would be open to electric cars, plug-in hybrids, and any vehicle that met the latest Euro 6 emissions regulations that went into effect last year – and carpools too, of course.
The Euro 6 rules had their greatest effect on the diesel vehicles that comprise roughly half of Europe's new car sales, bringing them up to the standard in effect for US sales since 2008.
The study will attempt to ascertain the effect of the "eco lane" on air quality as well as looking at ways to limit access to qualifying vehicles.
In general, hybrids, plug-in hybrids, and electric cars usually have at least a few exterior features – badges and labels, if nothing else – that distinguish them from gasoline vehicles.
But it could prove almost impossible to determine just by looking whether a vehicle meets the Euro 6 rules. And model year is usually not reflected by a car's registration number.
A similar proposal by the transport ministry in 2013 that would have allowed only electric vehicles in "eco lanes" went nowhere.
The new plan may meet with greater public acceptance given that the newest conventional cars could get access as well.
As the vehicle mix shifts over time toward a greater proportion of Euro 6-compliant vehicles on the roads, that access might have to be curtailed.
The study is expected to last for six months, followed by 12 months of public education and discussion of its findings.
One point of debate is likely to be the balance between lowering emissions and traffic avoidance via measures that encourage fewer vehicles to enter the city center.
As one participant noted, "A traffic jam of electric cars is [still] a traffic jam."