In an AdAge interview published yesterday, Toyota general manager Bob Carter covered an array of topics, such as Corolla sales, the consumer migration from full-size SUVs to smaller SUVs and crossovers, and Toyota's faltering reliability reputation as of late. But one thing stood out: Carter said that while Toyota Prius sales surged 67 percent in 2007 to a record 181,000 vehicles in the U.S., don't expect a repeat of that in 2008—the company simply can't build enough of them.

"Our volume on Prius was up 67% last year," Carter said. "That was a supply-restricted 67% increase. That's 181,000 cars. We can't repeat that, no way, even though the demand may be there. We just can't keep up. So you will see much more moderate growth because of the supply."

Instead, Carter said, Toyota and other manufacturers are working on not only hybrids, but figuring out what other technologies can deliver the same environmental and miles-per-gallon benefits. "We are very committed to hybrids, but it's not our position that hybrid is the solution to the future," he said. "We're looking at high-efficiency gasoline, clean diesel, fuel cells and the plug-in hybrid [as alternatives]."

Translation: Even though the Prius is a completely successful design and arguably the most environmentally-friendly car available today, we're at the limit of feasible production and have no choice but to look at other alternatives. That doesn't sound good at all.