since 1988 since 1988 since 1988 since 1988 since 1988 add another $1.4 billion to state coffers per year. since 1988 since 1988 since 1988 since 1988 since 1988 add another $1.4 billion to state coffers per year. Gas tax since 1988 since 1988 since 1988 since 1988