Source: BP Review
Oil is only 40% of our overall energy use.
We know that gasoline usage is about 10 million barrels per day. So, all you would have to do is quit selling gasoline to get down to about 9 mbpd.
If you increased the other fuel types by 10% each, you would be able to replace 3 of the 10 million. Toecutter would like this because people would start to go crazy converting their little hondas over to electric. Natural gas cars are easily doable, with current technology, but in light of recent reports, we might want to take it easy on the natural gas supply. Diesel: no problem.
Maybe you would be able to get another 1-2 million barrels per day out of biodiesel and some combination of ethanol and electric.
So you might be in the realm of feasibility if you could halve the fuel consumption of the existing car fleet. Since the average is now 22, and these hybrids get about 40, maybe this is close to doable.
Here is an old graph from the EIA on fuel use by type. Not much reason to think the ratios are too much different from these but this illustrates that there is some room for growth of alternatives.
Kochevnik is right, though, there would be some economic pain. This alternative implies keeping the auto fleet the same size, but converting it to use half as much fuel. But, to save even more, you would not let the auto fleet stay the same size. You let it contract temporarily to whatever size, and eventually replace everything with hybrids or electric. During the changeover, people would learn to do without some of this driving (conserve) and everything would eventually balance itself out at some lower level of energy consumption.
This would be a pretty serious undertaking, but if we absoutely had to, I think it could be done, for now. But in another 10 years, when our oil supply is even more depleted, and our vehicle fleet is much bigger, it will not be able to be done.
So that's the plan. Quit selling gasoline, let everybody figure out how to solve the problem any way they can, in about 5 years we have the problem fixed, temporarily, until the coal and gas run out.