The only way you’re going to get that kind of efficiency is to go with vehicles so light you can literally lift one end off the ground. And the wheels will have to start resembling wagon wheels...very tall, very skinny, and almost no rubber...and the car will have to be shaped like a raindrop, or a chicken egg.
I’m losing track of which replies you are replying to.
As far as a recumbant motorcycle with a half faring, the back end of the vehicle creates more drag than the front. It would be efficient only because of the minimal cross section. And you still have a motor cycle, cold weather, rain and all. College teams are already building vehicles with that cross section that get 1000+mpg.
As far as the vehicle under discussion, it has diesel engine, that would weigh a few hundred pounds, ditto for the frame and another hundred for the body. A couple of hundred pounds for various internal components. You won’t beable to lift one end off the ground And with proper aerodynamics you have a vehicle will have no problems hanging onto the ground.
This vehicle is not what I am looking for but I would love to have one of the small turbocharged diesel cars they are selling in Europe now. Nice driver that gets 60 mpg.