I would propose a system with gas-credits, like a creditcard.
Every car owner them will be entitled to buy a certain amount of gallons of gas every month.
These will be taken of your gas-credit-account.
Credits not spend can be saved for next month. Or can be sold to others via the internet.
Extra credits can be hand out tho those that give special service to the public, like house doktors.

The second thing I would propose is to abolish payroll tax and  
compensate the loss of government income by raising the tax on   oil products.

The idea of replacing the Social Security tax with a petroleum tax is one of the dumbest ideas that keeps popping up on TOD. How do you propose Social Security meet its obligations as petroleum supply declines?  There are those who believe retirees and the disabled deserve to starve or freeze because they failed to properly invest income they never had.
You'd have to have a mechanism to constantly adjust the (carbon, gas, etc) tax as sales volumes fall.  Maybe easier and less stressful for everybody to just have a much larger personal income tax exemption that adjusts yearly.
It is my understanding that American retirees as a group are one of the support bases for GWB and the Rethugs. It is hard to have sympathy for anyone who votes Republican yet cannot take care of themselves.  
No, they aren't. Rich, white retirees are more likely than not to be Republicans, but ordinary white people are not. It's just some people you know, not the many you don't.
I vote Republican, can take of myself and I have 14 families that depend on me (my employees) for good judgment.    How about that responsibility to navigate the PO waters.
tom deplume-

I don't think that replacing the Social Security tax with a petroleum tax would have any worse problems than the Social Security tax. For one thing, once there is little oil, there will probably be much less income to tax, so the Social Security system will have problems, no matter what we do.

I personally am pretty much a doomer when it comes to the US monetary system - I am afraid it will fail fairly early on, once people figure out about peak oil, and lending institutions stop making twenty or thirty year loans, including mortgage loans. Even the present downturn in the housing industry, if it gets worse, could hit the monetary system pretty hard.

Another thing to keep in mind is that at any point in time, there will be only so much of quite a few things available - oil, food, fresh water.  The current monetary system or some new monetary system can help divide these goods up, but it can't make any more than there is in total.

With all these issues, I think that people should not count on social security, medicare, medicaid, and other social programs. We may luck out and get a little from them, but if there is not enough to go around, social welfare progams are likely to be cut. Private pensions are not likely to fare a whole lot better - they depend on the stock and bond markets to fund them, and will have problems if there are many bankruptcies, or problems with the monetary system.

I have not always voted for the Dems but I have never voted for a Republican even though I am middle aged, Christian, a white man, and blue collar. Perhaps it's my impaired sanity.
There's a simple way around that, too:  use the fuel-tax money to rebate Social Security taxes on the first $X of income.  As fuel taxes decline, so does the rebate.
A much better idea, speaking as one who recently started an early draw of SS.  Those who don't want to plan on SS are welcome not to do so, but there are a lot of voters who have a certain attachment to the idea and a great many of us are not Republicans.