As to property, casualty, vehicle and surety insurance, and marine and transportation insurance other than as provided in Section 59A-8-10 N.M. Stat. Ann., the insurer shall maintain as a liability an unearned premium reserve on policies in force computed as follows: fifty percent of the gross premium in force on policies having one year or less to run and pro rata on those for longer periods, or pro rata for all premiums in force.