AASHTO WL-1, Guidelines for the Selection and Application of Warning Lights on Roadway Operations Equipment (December 2009), provides guidance on warning lights used on maintenance and operations vehicles. An introduction explains safety issues for both the maintenance vehicle and crew and for other drivers sharing the roadway. The guidelines discuss lighting issues and considerations, including vehicle color, adverse weather, ambient light, and visually complex environments. Chapters on lighting selection cover light source and signal colors and the choice between flashing and steady lights. Further sections address lighting layout and positioning, retroreflective tape and its effective intensity requirements, and sample specifications covering physical, functional, and lighting performance requirements. The guidelines were developed under NCHRP Project 13-02 based on experiments with many lighting configurations. Agency fleet managers and equipment specification writers can use the document when selecting and specifying warning lights.