ENHANCED REAR LIGHTING AND SIGNALING SYSTEMS TASK 2 REPORT: TESTING AND OPTIMIZATION OF HIGH-LEVEL AND STOPPED/SLOWLY-MOVING VEHICLE REAR SIGNALING SYSTEMS

Rear-end crashes account for approximately 25% of all crashes and result in a substantial number of injuries and fatalities each year. The goal of this research effort is to develop and test a small number of enhanced rear-lighting concepts that have the potential to reduce the number of rear-end collisions, including crashes with stopped or slowly-moving vehicles. This document reports on Task 2 of the research effort, which consisted of two experiments to design and optimize systems with regard to four dependent measures (Attention-Getting Rating, Discomfort-Glare Rating, Horizontal Peripheral Detection Angle, and Diagonal Peripheral Detection Angle) while also taking system complexity into account. In Experiment 1, 12 subjects evaluated 17 configurations. These configurations included variants of the Task 1 recommendations as well as baseline systems, including several highly attention-getting devices. Experiment 1 was conducted using white lights and clear lenses to provide a consistent comparison across all configurations. The results showed that the Traffic Clearing Light (TCL), a lamp with a motorized reflector moving in and "M-sweep" pattern, was the top candidate for a high-level signal (e.g., for imminent crash warning), while a pair of centrally located alternating halogen lamps would be optimal for a stopped/slowly moving vehicle signal. Experiment 2 also used a mixed factors design with 12 subjects to evaluate four configurations, (the TCL, along with three variations of the alternating halogen lamp pair) and three lens tints (clear, amber, and red). The results showed that the TCL was superior to the alternating pair configurations in attention-getting and peripheral detection and would thus be best used as the high-level signal with tinted lenses in either red or amber. The results also suggested that the high-output halogen alternating pair with dispersive lenses represents the best available configuration for the stopped/slowly-moving vehicle signal with tinted lenses in either red or amber. The final system recommendation is for an additional three-lamp bar to be mounted somewhere below the central high mounted signal lamp (CHMSL). The center lamp would be the high-level signal and would consist of the TCL with a nondispersive red lens. The outside signal pair would be the stopped/slowly moving vehicle signal and would consist of the high-output halogen alternating pair with dispersive amber lenses. The recommended final system is fully described in terms of functional requirements and system specifications. The report also contains an appendix describing the algorithms to be used for the activation of each signal type. These two elements combine to completely specify a promising rear signaling system to the point of readiness for further development and field or fleet testing.