Selectable 4WD/AWD and 2WD

[dezso3]

How come they don't make Subaru's with a part-time 4WD or AWD option, instead of making them all with full-time AWD? It could easily improve their fuel economy as well as their acceleration if the AWD could be switched on when the roads are snowy/icy. For example, the Subaru Impreza has an EPA estimated 20 MPG in the city and 27 on the highway, whereas a Toyota Camry, which has the same size engine, a 2.5L I4, but is only two-wheel drive (2WD), gets an estimated 22 MPG in the city and 32 on the highway. The Subaru Impreza is a great car, and if the company made cars that had a part-time four wheel drive option, I would most certainly buy one. Also, if you go to this link, you will see a picture of a Jeep's SELEC-TRAC shifter, with it having different options between 2WD, full-time 4WD, part-time 4WD, and 4-LO. I'm just curious, what do all these denote? What is the difference between them? And why is it that only a very few cars, such as the Jeep Cherokee, come with a selectable 4WD option? Companies such as Audi, VW, BMW, Acura, Ford, and GM all make sedans that range in size from small to large, but they are only available in either all-time 2WD or all-time AWD, with none of them having selectable AWD or 4WD like Jeeps do. And I would not buy a Jeep because they obviously use way too much gas and pollute the air.

Here's what the Jeep SELEC-TRAC shifter looks like: http://www.wjjeeps.com/st_shifter.jpg