(a) A driver may not use a hand-held mobile telephone while driving a commercial motor vehicle.
     (b) A motor carrier may not allow or require its drivers to use a hand-held mobile telephone while driving a commercial motor vehicle.
     (c) For the purpose of this Section, driving means operating a commercial motor vehicle on a highway, including while temporarily stationary because of traffic, a traffic control device, or other momentary delays. Driving does not include operating a commercial motor vehicle when the driver has moved the vehicle to the side of, or off, a highway and has halted in a location where the vehicle can safely remain stationary.
     (d) Using a hand-held mobile telephone is permissible by a driver of a commercial motor vehicle when necessary to communicate with law enforcement officials or other emergency services.