In addition to the license fees required under RCW 46.17.355
for registering vehicles under RCW 46.16A.455
, operators of auto stages with seating capacity over six shall pay, at the time they file gross earning returns with the utilities and transportation commission, the sum of fifteen cents for each one hundred vehicle miles operated by each auto stage over the public highways of this state. However, in the case of each auto stage propelled by steam, electricity, natural gas, diesel oil, butane, or propane, the payment required in this section is twenty cents per one hundred miles of such operation. The commission shall transmit all sums so collected to the state treasurer, who shall deposit the same in the motor vehicle fund. Any person failing to make any payment required by this section is subject to a penalty of one hundred percent of the payment due in this section, in addition to any penalty provided for failure to submit a report. Any penalties so collected shall be credited to the public service revolving fund.