GM built a 2-seat car, that actually looked like a car, in the early 1980s that got over 100mpg. It used a small gasoline engine. The car was very light. Being so lightly constructed, it would not pass the safety standards that get progressively higher each year. As such, the car was scrapped.
Why does a new Chrysler 300 weigh over 4000lbs? It is smaller than my 94 Crown Vic. The Crown weighs about 3700lbs. It is heavier primarily because safety standards have risen since 94. And, that takes more steel.
You cannot have it both ways. You either give up mass or you pay the fuel bill. You cannot cheat physics. Aerodynamics do play a part, but in reality, at highway speeds they are not that big a deal if the car is even remotely shaped like 50% of the cars on the road. most modern cars have decent drag valuves. It is the mass that gets you. Sure, Audi makes some cars that are all aluminum and weigh less....and they cost six figures. The average Joe cannot afford one.
You do not get much lighter than an aluminum semi monocoque structure. That is what Boeing builds. If there were something lighter, that is what airplanes would be made from. Composites are often heavier. Airstream needs to eliminate the corian and put in something lighter. Good grief my 34 foot triple axle Avion only weighs 6500lbs. So why do 27 foot trailers weigh more than that now?
Anyway, not to rant, but my education and training was in aerospace and mechanical engineering. I "m a pretty good mechanic, and I consider myself part of the "they" that come up with new designs for stuff. Just because some politician mandates something does not mean it can actually be done. You cannot cheat Newton. Right now, cars are too heavy to meet this reg for a total fleet average. GM already did it in 1983...imagine what they could do right now with modern fuel injection and a small 1 litre diesel. It just has to be made much lighter. I would love to build a nice looking sedan that had 400hp, was fun to drive, and got 150mpg. But it simply cannot be done. Electric motors are pretty good, but the battery technology is not there yet. Guys are working on it, but you cannot find an all electric car that can go 250 miles on a charge. And batteries deteriorate as they age, so the car that can go 200 miles on a charge on day one may only go 75 miles on a charge when it is six months old. the high powered fuel cells that NASA use are not safe to be around.
I have had this idea for a few years now to build a three wheeled car. It would use a small motorcycle engine driving a single back wheel, a tear drop shaped fuselage with super low drag, and two steering wheels up front. I was going to do a 4130 tube frame with fiberglass shell. I figure I could get 100mpg easily enough with it. But it would probably need to be licensed as a motorcycle. And again, you would not survive a crash against an F 350 with it like you would in a car.....
By the by, all diesel engines will run on vegetable oil. The exhaust smells like McDonalds.
For real! You want to filter out the french fry particulates first though....injector pump does not like them!
And if I could afford a Prevost, I would not complain about the gas!
Cheers,