Code of Federal Regulations Title 10. Energy § 10.708.2 Definitions

(a) Except as provided in subsection (b) of this Code section, every motor vehicle which is so constructed or loaded as to obstruct the driver's view to the rear thereof from the driver's position shall be equipped with a mirror so located as to reflect to the driver a view of the highway for a distance of at least 200 feet to the rear of such vehicle.

(b) Every commercial motor vehicle shall be equipped with two rear-vision mirrors meeting the requirements of the federal motor vehicle safety standards contained in 49 C.F.R. 571.111 in effect at the time of manufacture, one at each side, firmly attached to the outside of the motor vehicle, and so located as to reflect to the driver a view of the highway to the rear, along both sides of the vehicle;  provided, however, that only one outside mirror shall be required, which shall be on the driver's side, on a commercial motor vehicle which is so constructed that the driver has a view to the rear by means of an interior mirror.