The purpose of this project was to establish a national performance standard for light-emitting diode (LED) signal lights at highway-railway grade crossings. The project first examined the existing performance standards for incandescent signal lights for grade crossings and traffic lights. In consultation with a broad spectrum of stakeholders, basic criteria were established for a new standard that would apply to LED signal lights at grade crossings. The scientific and technical literature on LEDs, human factors, and driver requirements was then summarized and analyzed, resulting in a tentative performance standard that specified light output and beam pattern, as well as electrical, mechanical and quality assurance requirements. This standard was tested in the laboratory and in three field experiments to determine its feasibility and its effectiveness relative to existing incandescent signal lights. The results showed that the performance requirements could be met by existing LED technology, and clearly demonstrated the superior performance of the LED signal lights. The standard requires that LED signal lights produce 400 cd light output, on axis, under all conditions likely to be encountered in the field and over the lifetime of the product. The beam pattern must equal or exceed international traffic light requirements, resulting in a much broader beam pattern than existing railway requirements. In conclusion, a verifiable performance standard was developed that provides for improved conspicuity of grade crossing signal lights through the adoption of LED technology.
Abstract