In a standard 2 wheel drive with a standard differential, if one driven wheel breaks loose, it spins and the rest do nada, zip, bupkis. If you have a "limited slip" differential, then if one wheel slips, the differential locks both wheels together which puts power to both wheels. 4 wheel drive is just that, two differentials, one in front and one in back, thus driving all 4 wheels. 4 wheel drive has clutches and locking hubs so you can disengage the front wheels from the drive train. In all wheel drive, on level straight pavement, all 4 wheels get power all the time equally, so if one slips on a patch of ice, so what? The other three are still getting power. 4 wheel or all wheel drive get you going better than simple 2 wheel drive, but that is all the advantage you get. When it comes to stopping, it makes NO difference. Stopping is all brakes and traction where the rubber meets the road. People with all wheel drive tend to get into MORE accidents in winter on ice because they do NOT believe that it makes no difference once you start skidding on ice and in fact with all wheels spinning under power may actually prevent you from regaining steering from turning into the skid because of the power spinning the wheels. When skidding on ice, the best you can do is off the gas, off the brakes and turn the wheels in the direction of the skid. Ironically, the one car you would think worst, a rear engine drive vehicle actually is the easiest to get out of a skid. Front wheel drive takes a close second if you accelerate while turning into the direction of the skid. I live in the Pacific Northwest, west of Seattle. We get a lot of heave rain here and in winter, sometimes snow and ice. In the 20 plus years I;ve been here, of the cars which end up in the ditch, MOST are all wheel drive. My VW microbus (rear engine and drive) and Geo Metro (front engine and drive) may be 2 wheel drive without limited slip differentials, but I've never ended up in the ditch, but I've seen some less than careful impatient drivers who passed me end up there... And I always stop to make sure no one has been hurt and they can call a tow truck to pull them out... Like I said, all wheel drive may help get you going on a hill or from a stop at a stop sign, but it does NOTHING to help you stop. Being a careful driver is better to count on than all wheel drive. People who say all wheel drive is safer, are blowing smoke. All wheel drive IS helpful to a certain extent on slick roads. I am NOT trying to talk you out of it at all. I just want for you to be aware of the fallacy that all wheel drive is safer. Safer is how well you can decelerate, not accelerate. Brakes and tires in good condition do more to reduce severity of accidents than any other factor.