(1) A use tax is imposed on compressed natural gas used for the propulsion of motor vehicles on the public highways of this state. For the purpose of determining the tax on compressed natural gas, a gallon equivalent factor of five and sixty-six one-hundredths pounds (5.66 lbs.) per gallon shall be used. The rate of the tax imposed by this section shall be: On or after July 1, 2017, through June 30, 2018, sixteen cents (16¢) per gallon;
(2) On or after July 1, 2018, through June 30, 2019, eighteen cents (18¢) per gallon; and
(3) On or after July 1, 2019, twenty-one cents (21¢) per gallon.
(4) Governmental agencies are exempt from the compressed natural gas tax imposed by subsection (a).