Optional on our trucks, the rule (from
http://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+46.2-1017) is:
All motor vehicles, trailers, or semitrailers exceeding seven feet in width or the widest portion of which extends four inches beyond the front fender extremes shall be equipped with amber lights mounted at the extreme right and left front top corners of such vehicle. Each such light shall be visible in clear weather for a distance of at least 500 feet to the front of such vehicle. Such vehicles shall also be equipped with red lights mounted at the extreme right and left rear top corners of such vehicle. Each such light shall be visible in clear weather for at least 500 feet to the rear of such vehicle. Any tractor truck, however, need not be equipped with rear red dimension or marker lights. If the front or the rear of such vehicle is not the widest portion of the vehicle, the dimension or marker lights required in this section shall be mounted on the widest portions of the vehicle with the amber lights herein required visible from the front as herein required and the red lights herein required visible from the rear as herein required. The lights herein required shall be of a type approved by the Superintendent.