well, I have the 06 Jetta TDI... If asked overall average for highway I would guess it to be around 55 mpg.
The brand new ones supposedly dont get that now.
....its all about the horse power weight ratio. say you have 400 hp, and your vehicle weighs 8000 lbs, without resistance it might take 250 hp to move the truck. now start factoring in the energy to compress the air and you might end up using 350 of that 400 HP your available power to compress the air is reduced so inadvertently the top speed while towing is also reduced along with the fuel economy.
Yes, so if you build a boxy-shaped heavy vehicle with a gasoline engine which is underpowered for the size of the vehicle, you consume enormous amounts of fuel to push it forward. Strap it down with a bunch of unnecessary emission-controls (selling it as "green" to idiot lefties), it's even worse. Put those controls in the tailpipe's catalytic converter instead of putting particulate platinum in near the combustion area instead and you're wasting even more fuel. What lefties aren't doing the math on is how many more gallons of fuel will have to be burned to move the car between two points.
Build a streamlined jetta like VW has using diesel's high torque and power compared to weaker gasoline engines, reining in emission-control-overkill and you get 50mpg. Many jettas were using what a 1.9 liter motor and getting great power and mileage. Jettas aren't light vehicles by the way; try to push a dead one with your friends. Try running a 1.9 liter gas motor in a jetta body...lol... It might make it out of your driveway...maybe. Diesels are superior to gasoline, period. Much less fuel burned (and going into the atmosphere therefore) than the "green" "emissions controlled" gas clunker.
BigOil knows all this all too well and has for decades. That's why when clean-air Europe drives the crap out of small passenger diesel cars, you only extremely rarely see windows open, then quickly slam shut over here on opportunities to buy one. BigOil doesn't want Americans seeing their neighbors bragging at BBQs about how their jetta or bug gets 50-60 mpg highway routinely. That puts BigOil out of business. Add to that that diesel can be cut with biofuels grown from algae and other bio sources, and BigOil gets doubly scared.
Odd that "suddenly" VW has a big emissions scam. I vote that the person(s) responsible at VW were paid well in their moonlight job of saboteurs for BigOil.