Hazardous Materials Transportation Authorization Act of 1993 - Amends the Hazardous Materials Transportation Act to authorize appropriations for FY 1994 through 1996 for the regulation of the transportation of hazardous materials. Exempts from the requirement to file a registration statement persons domiciled outside the United States who offer, solely from a location outside the United States, hazardous materials for transportation in commerce. Directs the Secretary of Transportation (Secretary) to make grants to Indian tribes for the development of emergency response plans with respect to the transportation of hazardous materials through Indian lands. Requires States or Indian tribes receiving such grants to ensure that such emergency planning is coordinated with emergency plans conducted by adjacent States and Indian tribes. Requires States, local governments, or Indian tribes that levy fees in connection with the transportation of hazardous materials to comply with certain disclosure requirements. Changes from annual to biennial the Secretary's periodic comprehensive report to the President (for transmittal to the Congress) on the transportation of hazardous materials. Directs the Secretary to ensure that the National Intelligent Vehicle-Highway Systems Program addresses the use of intelligent vehicle-highway system technologies to promote hazardous materials transportation safety. Requires the Secretary to issue final regulations under specified dockets concerning: (1) crashworthiness protection requirements for tank cars; and (2) detection and repair of cracks, pits, corrosion, lining flaws, thermal protection flaws and other defects of tank car tanks. Directs the Secretary to study the existing practices regarding the placement of cars on trains, with particular attention to the placement of cars carrying hazardous materials. Requires the Secretary to amend regulations under the Hazardous Materials Transportation Act and the Motor Carrier Safety Act of 1984 to prohibit the driver of a motor vehicle transporting hazardous materials in commerce or of any commercial vehicle from driving it onto a highway-rail grade crossing without sufficient space to drive completely through the crossing without stopping. Requires the Secretary to issue regulations to require that any document bearing on the record of duty status of a driver who operates a commercial motor vehicle: (1) be retained by the employing motor carrier for at least six months after receipt; and (2) include information identifying the driver and vehicle. Directs the Secretary to amend the Code of Federal Regulations (CFR) with respect to the acquisition of safety performance histories of new drivers employed by a motor carrier. Requires the retention of shipping papers by persons who provided them and the motor carrier required to maintain it after the hazardous material involved is no longer in transportation. Requires the Secretary to establish a toll-free "800" telephone number for transporters of hazardous materials and other individuals to report possible violations of the Hazardous Materials Transportation Act or any regulation issued under this Act. Requires the Secretary to exempt farmers and retail farm suppliers from CFR hours of service requirements when they transport supplies for agricultural purposes within a 50-mile radius of their distribution point during the crop-planting season.