Some form of hybrid electric drive looks like the wave of the future, or at least the near-term future, and a diesel-electric hybrid would seem to be the best of both worlds. That’s because the electric portion of a hybrid powertrain offers its primary benefit in stop-and-go low-speed city driving, while diesels are at their best cruising steadily along at highway speeds. Why not marry them?

The short answer is cost. Two-mode hybrid vehicles have two powertrains, one internal combustion and one electric. The electric portion is the expensive one, largely because of the cost of the big, powerful, exotic battery it must use. Add to that a diesel, which is far costlier than a gasoline engine, and you have two high-cost powertrains on one chassis. (Learn how hybrids work.)

Even in Europe, where diesel cars comprise about half the new-car sales, economies of scale have not brought diesel prices in parity with gasoline engines. Because a diesel must cope with significantly greater operating pressures than gasoline engines, the engine itself has to be much beefier.

On paper, and maybe on the road some day, a diesel electric hybrid could be the best of both worlds. As was said during our Future of the Car day panel discussion: “Combining the technologies can lead to great efficiencies in power and emissions, however there is cost and question if market will bear it.”

What do you think? Would you pay a premium for such a powertrain?

—Gordon Hard