With their ability to drive solely on electric power at low speeds, hybrids appear better suited to city driving, while diesel drivers have been known to exceed their vehicles' rated fuel economy on the highway.
Those perceptions are confirmed by a new study of U.K. data from research firm Emissions Analytics, which found that in terms of fuel economy, on average, hybrids do best in cities, while diesels do best on highways.
Note that this study used U.K.-market vehicles, which are rated using the highly-optimistic European testing cycle. The specific models surveyed also aren't available in the U.S.
The study found that both types of powertrain did worse in city driving than highway driving--but the penalty was worse for diesels than hybrids.
It was 7 percent for diesels, but only 3 percent for hybrids--which makes sense considering that many hybrids have higher rated city mpg than highway mpg, while it's usually the inverse for diesels and other vehicles that rely solely on internal-combustion power.
Researchers said any advantage hybrids might have evaporated in highway driving, where diesels appeared much better suited to the conditions.
While the U.S. EPA test cycle is tougher than the European standard, those results likely won't surprise U.S. drivers.
While diesels have been know to easily meet--or even exceed--their EPA highway ratings, hybrids seem more sensitive to factors like driving style, and sometimes have trouble matching their fuel-economy ratings in the real world.
Hybrids did have an advantage in another area, though.
Researchers noted that hybrids produce consistently lower levels of nitrogen-oxide emissions than diesels, especially in urban driving, when some zero-emission driving on electric power is factored in.
So while diesels may return more consistent fuel-economy results, hybrids remain the cleaner choice.