(a) If, after having obtained a license under Section 40-12-248 for any truck or truck tractor, the owner thereof voluntarily applies for a license of greater cost than that previously obtained, the cost of the new license shall be computed on the quarterly declining basis as of the date such license was lawfully due, and credit for the old license shall be allowed on the basis of the value of the surrendered license for the corresponding quarter, it being the intent and purpose of this section that the remaining value of the surrendered license be allowed as a credit on the purchase of the higher license and that the cost for increased weight allowance or for use as a for-hire or leased vehicle date from the time of the first use of the vehicle at the greater weight or from the commencement of the lease or the for-hire operation.

(b) If, by virtue of citation or assessment by any agent of the state charged with the enforcement of this section, an owner is required to purchase a license of higher cost for exceeding the allowed gross vehicle weight for which licensed or for use of the vehicle in a manner for which proper license has not been voluntarily obtained prior to such citation or assessment, the quarterly declining basis shall not be allowed, and the full license must be obtained, although credit for the license previously obtained shall be allowed. A penalty of 25 percent of the net amount of the license due shall be collected, plus interest as now provided by law. The penalty hereby imposed may not be waived.