VOLUNTARY WOULD BE BETTER:

How $3 gas could push US drivers to shift: But consumption habits would only change if prices stay high (Mark Trumbull, 5/03/06, The Christian Science Monitor)

To politicians, high prices have exposed a more urgent need for measures that help the nation diversify beyond oil-based transportation. To consumers and producers of energy, the marketplace is providing an impetus for new products and resource-saving habits. [...]

For years, some policy experts and economists have argued that higher taxes on gasoline - or on fossil fuels in general - would be the most efficient way to curb demand for oil and promote alternatives. What the nation now faces is a kind of involuntary test of those proposals.