The feds and the states apply a fixed price per gallon tax, the price of gas has dropped which allows more people to purchase more for the dollar which means more gallons purchased and more taxes generated. There is no reason for raising gas taxes. Now state severance taxes on oil and gas are taking a big kick in the pants, they are based on percentage per barrel and unit. They are seeing an almost 50% drop in revenue.
After seeing a 100 percent increase, and more, over the past few years.