Once the tax incentives for hybrids go away, hybrids will too. They basically short circuit the EPA's broken method of measuring mileage. You'd think the EPA would do it the logical way - run the test cycle over and over until they burn off 10 gallons or so, then figure out the average mpg. Nope - they do it via some broken statistical analysis of the car's emissions. Toytota figured out how to short circuit that method and get great numbers.
Realistically, a Prius without the hydrid stuff, the batteries, etc would likely get the same mileage. But nobody today could sell a 70hp car that gets 40mpg - it just won't sell. And on an MPG per HP bassis, the Prius is worse than a Corvette - it's got barely 100hp (and that's including the shot in the arm motor, not just the lethargic gas engine), yet gets 10-15mpg better than a Corvette with more than 4 times the power...
The bigt issue is the driving cycles where hybrids work should best are the same kinds of cycles that are hell on batteries. Once again, battery technology just isn't there.
Even hybrid transit busses are now believed to not have the emissions or mileage advantages they thought they would. i suspect you'll see them, though, because of the 'PC' factor (why must transit in the US be sold on political correctness as opposed to overal system useability?!?), and because hybrid buses have other advantages - better low end punch, ease of low floor design, easier noise control.
Even the most rosy predictions for hybrid cars now place them at no more than 10X of the market (if that!). The public will, of course chose, and so far, hybrids aren't a very good sell.
What's sad is, if they'd just chop 500 lbs off most cars, they'd get much better mileage AND be faster too.
The other biggie will be better undercar air management - that's starting to show up now. Big gains there.
Hybrids came along because it became blindingly obvious in the late 90's that California's battery car mandate wasn't going to be met (because there's STILL no decent electric cars out there, and likely wion't be), and they had to 'do something'. Why bother? Today's SULEV car will emitt 1 pint of hydrocarbons over 100,000+ miles. You'll litterally SPILL more gas gassing it up than it'll pollute. Realistically, the big HC emissions gain would be a new and better fueling system for cars - prefferably one that locks the nozzle into the filler and takes care of itself while you do the windows and such (as opposed to those horrid vapor recovery ones that you have to sit on or they'll shoot out). As far as NOx and CO are concerened? Catalysts are still getting better, today's engines have such little engine out emissions that further rdeductions are really giving diminishing returns. CO2? Sure, why not regulate how much people breathe too, then (after all, people emit lots of the stuff 24/7 car or no car...)
