When looked at in pure dollars and cents, there are many cases in which electric cars don't yet provide a payback.

But other forces will boost their chances of adoption beyond pure payback. And government regulations are one of those forces.

On Monday, the European Commission will issue a road map on transport from now until 2050.

According to one source, it includes a goal for all European city cores to become zero-emissions zones by 2050 or sooner.

It's part of a much broader collection of measures to reduce greenhouse-gas emissions throughout the transport sector by 60 percent over 2010 levels.

It includes recommendations for freight-rail transport, higher taxes on cars that consume more petroleum-based fuels, and many other policies.

We've often commented that one of the forces behind pricey plug-in hybrid sports and luxury cars, from the Porsche 918 Spyder to the Mercedes-Benz S 500 Plug-In Hybrid, is the likelihood that wealthy people will want to drive their own cars into business districts--even if those districts only allow zero-emissions vehicles.

London now forgoes its Congestion Charge for weekday entry to the city core if you're driving an electric car. And Paris is planning on experimenting with its own entry fee as well, regulating the different types of vehicles that enter the city center.

Such a prospect is much harder to imagine for U.S. cities, especially given the extreme political wrath heaped on New York City mayor Mike Bloomberg when he has proposed tolls on the East River bridges and tunnels that connect Manhattan to the rest of New York City.

Nonetheless, European political goals may well have a direct impact on the number of plug-in vehicles offered for sale and the pace of electric-car technology development.

And that can't be bad, right?