Under a gas tax regime that actually significantly decreases demand, even a person who consumes below the average consumption will be negatively impacted, especially if he/she is of low or moderate income.

You're assuming that the tax is increased in isolation.  Why?  No less a luminary than T. Boone Pickens has suggested that employment taxes be reduced by the same amount as fuel taxes increase.  This would put money back into the pockets of workers, most of it at the low-income end where employment taxes weigh most heavily.

Rationing is as damaging as the 70's-era gasoline allocations (which produced long gas lines in some parts of the USA and no waits elsewhere).  It fails to influence behavior except at a very arbitrary dividing line.  Take me as an example.  I go through an 18-gallon tank about every 2-3 weeks; if the ration was set at the average consumption of about 12 gallons/week, I'd have plenty left over.  I'd have no incentive to change; I could save fuel, but it wouldn't pay me anything to compensate for the inconvenience.  Neither would it give me any breathing room for an emergency.

A fuel-tax increase would pay me every time I didn't drive someplace, every time I coasted up to a traffic light (which I already do), and for every other act which cuts fuel consumption.  If it was offset by a cut in my FICA taxes, I could just pocket that money and live better.  Rationing has no upside.