The basis for system integration and field testing was developed for assessing a dilemma zone warning system for signalized intersections. The system consists of hardware (an in-vehicle warning device, roadside antenna, and traffic signal controller) and software to operate and test the integrated component warning and communications systems. Field tests were conducted in real traffic situations to test the system's warning initiation time from the signal controller, the activation and duration of the visual and audible signals, and the warning delay, on the basis of relationships between distance variables that include the safe stopping distance and the location of roadside antenna. Findings from the field tests at two signalized intersections indicated that the system could be implemented at signalized intersections to eliminate the dilemma zone, relative to approach speeds, and to reduce red-light violations and intersection collisions by means of an in-vehicle warning device.