A variable gas tax is proposed by Bradley, Ridge, and Walker in The Road to Recovery: Transforming America’s Transportation(Carnegie Endowment, 2011) as a way to secure transportation funds, while at the same time stabilizing gas prices at the pump. Revenue is generated by a combination of an oil security fee, a gas tax, and a diesel tax. A ‘trigger price’ for crude oil is specified, below which the gas and diesel taxes are applied and above which the gas and diesel taxes are abated. TRUTHstudio created an interactive dashboard that enables policy analysts to experiment with different possible trigger and market prices, immediately immediately seeing the results in terms of revenues and prices at the pump. The four charts in the interface show the composition of revenue (top chart) from taxes and fees (bottom 3 charts) at different crude oil price points. In the interactive version, the charts adjust dynamically as the trigger price and market price change. 
link to report