I'm sure it would work like Flexible Spending Accounts too, where anything left in it at the end of the year is histoire. And exactly, why not just cut the fuel tax? They could give that the same 2 year sunset provision. How much you want to bet this "pre-tax income" would be paired with a new gas tax, resulting in either a zero sum game or probably even more tax burden than the prior arrangement.
It's also another element of their plan to render ever citizen dependent on government. Dependent for welfare, for food stamps, for unemployment, for Medicaid, for "fuel savings accounts", blah blah blah. Jefferson wrote something about "evinces a design...".