A vanpool refers to a commuter highway vehicle, which is any highway vehicle with a seating capacity of at least six (6) adults (excluding the driver); and of which at least eighty percent (80%) of the mileage for a year is reasonably expected to be used: for purposes of transporting employees in connection with travel between their residences and their places of employment; on trips during which the number of employees transported for such purposes is at least one-half (1/2) of the adult seating capacity of such vehicle (excluding the driver)