(a) Any police officer having reason to believe that the weight of a vehicle and load is unlawful shall require the driver to stop and submit to a weighing of the same either by means of a portable or stationary scales that have been tested and approved at a frequency prescribed by the Illinois Department of Agriculture, or for those scales operated by the State, when such tests are requested by the Illinois State Police, whichever is more frequent. If such scales are not available at the place where such vehicle is stopped, the police officer shall require that such vehicle be driven to the nearest available scale that has been tested and approved pursuant to this Section by the Illinois Department of Agriculture. Notwithstanding any provisions of the Weights and Measures Act or the United States Department of Commerce NIST handbook 44, multi or single draft weighing is an acceptable method of weighing by law enforcement for determining a violation of Chapter 3 or 15 of this Code. Law enforcement is exempt from the requirements of commercial weighing established in NIST handbook 44. Within 18 months after the effective date of this amendatory Act of the 91st General Assembly, all municipal and county officers, technicians, and employees who set up and operate portable scales for wheel load or axle load or both and issue citations based on the use of portable scales for wheel load or axle load or both and who have not successfully completed initial classroom and field training regarding the set up and operation of portable scales, shall attend and successfully complete initial classroom and field training administered by the Illinois Law Enforcement Training Standards Board.