Under sponsorship from the National Highway Cooperative Research Progr
am, tile authors have conducted extensive research in investigating th
e use of LEDs in traffic signals. The purpose was to determine whether
LEDs offer advantages in such applications while maintaining the requ
ired safety and performance aspects. Factors investigated were the pos
sibility of reduced power, decreased maintenance costs because of very
long life, and improved lumen maintenance. There were numerous safety
considerations such as intensity, chromaticity, and related human fac
tors. Further significant matters are environmental conditions and the
ir effect on these light sources. The ultimate objective of the work h
as been to demonstrate and evaluate the new technology to determine it
s feasibility, and to provide recommendations for possible changes to
traffic signal standards. A 2-year period of extensive testing and eva
luation has been completed. This effort has included the develop ment
of prototype signals of the three colors and a range of types. Extensi
ve photometric design and analysis have been conducted, both under lab
oratory and field conditions. Field installations have been made for h
uman factors testing under controlled conditions, as well as using the
devices for experimental controlled intersections. Many conclusions h
ave been developed, commenting on all significant factors. The researc
h work and these conclusions are summarized in the paper.