Every police officer, including members of the state highway patrol, having reason to believe that the weight of a vehicle and the load carried thereon is unlawful, may weigh such vehicle and load or have the same weighed either by means of portable or stationary scales, and for that purpose the officer may require the vehicle to be driven to the nearest scales. Such officer may require the driver of such vehicle immediately to unload such portion of the load as may be necessary to decrease the gross weight to the maximum allowed by the provisions of this chapter.