Our goal is to get all cars out of private hands. In the beginning, however, it might be worthwhile to target the most dangerous, the most environmentally damaging, and the most outright obnoxious cars. In other words: the biggest cars.
As I travel the streets of Southern California, I have noticed an interesting correlation: the least competent drivers always want to drive the biggest SUVs and vans. This makes them feel a lot safer, but puts the rest of us in a state of constant risk. How many times have we all nearly been forced off the road by some ultra wide vehicle whose driver can not keep it in their own lane? How man questionable right turns have we made on red lights because (tall and opaque) SUV in the left turn lane has pulled it all the way into the cross walk, blocking our view?
When these vehicles get in a collision, the results are devastating. Kinetic energy is directly proportional to mass. At a given speed, a vehicle that weighs twice as much will transmit twice as much energy to the object with which it collides.
I will not even address the driving habits of red-neck jack asses in jacked-up pickup trucks.
My point is, bigger vehicles are harder to control and more hazardous for other road users. The people who want them most are usually the ones who should not have them.
Environmentally, it is clear that larger vehicles are more damaging. The use a lot more material, all of which will eventually need to be recycled or otherwise disposed up. I would direct you to Katie Alvord's excellent book Divorce Your Car (New Society Publishers, 2000) for a discussion of the direct and indirect costs of manufacturing, maintaining, and disposing of cars. It is likely that most of these costs are proportional to weight.
Obviously, larger vehicles waste much more fossil fuel, which should be a concern to everybody. Likewise, they release many more pollutants into the atmosphere. In the US they are required to meet much laxer emissions standards than normal cars.
There is a simple way to attack the drivers of thees dangerous and wasteful vehicles. Most states currently require commercial drivers licenses for vehicles above a certain gross vehicle weight (GVW). In most states this kicks in around 10,000 lb GVW. A rather simple change in the motor vehicle code would redefine commercial vehicles as being any vehicle over 6,000 GVW. This would include most large SUVs, full sized vans, and pickup trucks. See here for a list of vehicles.
The change would require that anyone owning one of these vehicles would need to register them as commercial vehicles (which typically costs more and requires more paperwork than private vehicles). Their insurance rates would probably increase. Most importantly, they would be forced to obtain commercial licenses.
Most people who actually need to drive these vehicles for work probably already have a CDL, or could get one fairly easily. It could provide a useful barrier, however, for the sort of driver we have been speaking about.
The federal Department of Transportation (DOT) has guidelines for the issuance of a commercial drivers license. In general applicants must pay extra fees, take an additional multiple choice test, pass a road test in a commercial vehicle (which usually requires a special appointment), pass a comprehensive physical (which they must repeat every two years), and undergo a federal background check.All of these requirements are perfectly reasonable for someone who wants to operate a vehicle heavier than 6000 lbs. Indeed, they are rather modest considering how dangerous, dirty, and environmentally damaging they are. Hopefully some day we can outlaw them altogether. For now, we can change the laws to make them harder to operate.