The FHWA is amending the Federal Motor Carrier Safety Regulations (FMCSRs) to require that motor carriers engaged in interstate commerce install retroreflective tape or reflex reflectors on the sides and rear of semi-trailers and trailers that were manufactured prior to December 1, 1993, have an overall width of 2,032 (80 inches) or more, and a gross vehicle weight rating (GVWR) of 4,536 kg (10,001 pounds) or more. The FHWA is requiring that motor carriers install retroreflective tape or reflex reflectors within two years of the final date of this rule. The agency is allowing motor carriers a certain amount of flexibility in terms of the colors or color combinations during a 10-year period beginning on the effective date of this rule, but is requiring that all older trailers be equipped with conspicuity treatments identical to those mandated for new trailers at the end of the 10-year period. The locations at which the retroreflective tape or reflex reflectors must be applied to trailers during the phase-in period is specified. This rulemaking is intended to help motorists detect trailers at night and under other conditions of reduced visibility, thereby reducing the incidence of passenger vehicles colliding with the sides or rear of trailers . . . The effective date for the final rule is June 1, 1999.