[Code of Federal Regulations] [Title 49, Volume 4] [Revised as of October 1, 2002] From the U.S. Government Printing Office via GPO Access [CITE: 49CFR393.24] [Page 1059] TITLE 49--TRANSPORTATION CHAPTER III--FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION PART 393--PARTS AND ACCESSORIES NECESSARY FOR SAFE OPERATION--Table of Contents Subpart B--Lighting Devices, Reflectors, and Electrical Equipment Sec. 393.24 Requirements for head lamps and auxiliary road lighting lamps. (a) Mounting. Head lamps and auxiliary road lighting lamps shall be mounted so that the beams are readily adjustable, both vertically and horizontally, and the mounting shall be such that the aim is not readily disturbed by ordinary conditions of service. (b) Head lamps required. Every bus, truck, and truck tractor shall be equipped with a headlighting system composed of at least two head lamps, not including fog or other auxiliary lamps, with an equal number on each side of the vehicle. The headlighting system shall provide an upper and lower distribution of light, selectable at the driver's will. (c) Fog, adverse-weather, and auxiliary road-lighting lamps. For the purposes of this section, fog, adverse-weather, and auxiliary road lighting lamps, when installed, are considered to be a part of the headlighting system. Such lamps may be used in lieu of head lamps under conditions making their use advisable if there be at least one such lamp conforming to the appropriate SAE Standard 1 for such lamps on each side of the vehicle. --------------------------------------------------------------------------- 1 Wherever reference is made in these regulations to SAE Standards or SAE Recommended Practices, they shall be: (a) As found in the 1985 edition of the SAE Handbook with respect to parts and accessories other than lighting devices and reflectors. (b) When reference is made in these regulations to SAE Standards or SAE Recommended Practices, they shall be as found in the 1985 edition of the SAE Handbook: (1) With respect to parts and accessories other than lighting devices and reflectors: (2) Lighting devices and reflectors on motor vehicles manufactured on and after March 7, 1990, shall conform to FMVSS 571.108 (49 CFR 571.108) in effect at the time of manufacture of the vehicle. Should a conflict arise between FMVSS 571.108 and a SAE Standard, FMVSS 571.108 will prevail. --------------------------------------------------------------------------- (d) Aiming and intensity. Head lamps shall be constructed and installed so as to provide adequate and reliable illumination and shall conform to the appropriate specification set forth in the SAE Standards 1 for ``Electric Head Lamps for Motor Vehicles'' or ``Sealed- Beam Head Lamp Units for Motor Vehicles.'' [33 FR 19735, Dec. 25, 1968, as amended at 41 FR 53031, Dec. 3, 1976; 53 FR 49397, Dec. 7, 1988]