"The construction of an average car consumes the energy equivalent of approximately 20 barrels of oil, which equates to 840 gallons, of oil. Ultimately, the construction of a car will consume an amount of fossil fuels equivalent to twice the car's final weight."

So, to replace the 225 million or so automobiles in the U.S., it would require approximately 225M*20bbl = 4.5 billion barrels of oil to replace all the existing cars, or about a half-year's-worth of consumption in the U.S.

Of course, to replace all the cars in the world, it would take even more oil...

And I'm sure I'm missing some energy inputs in this calculation.

At $20,000 a piece, all these new cars would cost people in the US about $4.5 trillion. I'm sure the auto manufacturers would be into this plan...

No need to kill off billions--though Malthus was right, in the long run.

But wait a minute . . . in the long run, we're all dead, as John Maynard Keynes pointed out.

Note that the Roman Empire did not fall due to overpopulation--just the reverse!

Well said.  These alternatives transport methods will obviously help, but the headwinds created by the desire of personal convenience and time savings of one-two person transport will oppose this shift.  To what degree is hard to determine as fuel prices increase, but I expect to see an future explosion of bicycles, scooters, street-legalized quad ATVs, and motorcyles in places of urban sprawl [like my Asphalt Wonderland].

I have posted before about keeping your used pickup or SUV for the occasional hauling of large loads or 3 or more people [or when the weather is simply atrocious], but buying a used small scooter/ATV for one-two person commutes or errands.  Bicycles best of all, of course.  I presently feel this is the most cost-effective way to be prepared if gasoline suddenly spikes out of sight.

My eleven year old pickup is only worth maybe $2000-2500, but only has 115,000 miles on it-- many years of life left on it.  My recently bought used 2004 scooter: only 1600 miles [yes, only sixteen hundred!]-- estimated lifetime virtually unlimited until gas prices rise so high that some punk shoots me while I wait at an intersection to then steal my little scoot.

As a plus, sparetime hauling stuff for cash has easily paid for all the pickup's running expenses, and provided me with beer money.  A lot of people would rather pay someone than rent a U-Haul pickup to do it themselves.  Phx has a lot of 'bling-bling' pickups and SUVs with very expensive aftermarket accessories; I call them an ornate 'chrome penis'-- the last thing they want to do is fill the storage area with manure or crushed desert rocks for landscaping.

Bob Shaw in Phx,Az  Are Humans Smarter than Yeast?