If it doubled all but the wealthy would be off the roads. But that's true of everything - the wealthy are always last to be able to afford something. In fact, by and large the poor are already driving cars they can't afford paid for with money they don't have, which is proving a very shaky pillar of our economy, so reducing the debt burden would be no bad thing.
As sad as it would be, providing motorised access to the road for the poor, the middling, or even the wealthy, takes a back seat to reducing pollution death and Ill health, and environmental damage. Youre poor, eh? Oh so sorry, carry on pollutimg then.