The goal of this research was to assist the California Department of Transportation (DOT) in optimizing the message content and presentation within changeable message signs (CMS). Optimized content will improve information transfer while at the same time minimizing the likelihood of congestion owing to slowing by motorists attempting to read the message. The research was restricted to simulated signs displaying 16 characters in each of three lines, representing permanent CMS displays, or signs containing only 8 characters in each of three lines, as is the case for portable CMS displays. While all information can be contained in a single screen for the permanent signs, multiple screens are often required for the portable CMS displays. This study specifically focused on “early vision” which is distinct from “cognitive processes”. Early vision problems are those relating to the limitations of the first several stages of the visual system. An example question of early vision is whether flashing the letters ‘NB’ on a CMS message is more effective than leaving them steadily on. For these questions of recognition, accuracy is used as a measure of intelligibility. Cognitive process limitations, by contrast, involve events that are due to thinking on the part of the observer. An example of a question involving a cognitive limitation is whether observers interpret the abbreviation ‘NB’ as meaning ‘north bound’.

The project was divided into two phases, a laboratory phase and then a field test.

New technologies have enabled the production of traffic signals that have significant advantages over standard incandescent signals, including greater energy efficiency and lower maintenance costs. Before the new signals are installed in the field, it is important to assure that they as visible as the older signals. We have developed a quality index we term the usability factor (UF) which can be used to evaluate the visibility of a new device relative to that of a standard reference lamp. We have measured UF's of a variety of new types of lamps by means of heterochromatic flicker photometry. We have found UF's ranging from 0.55 to 1.35 for centrally-viewed targets under standardized viewing conditions. We also report measurements made under conditions of reduced visibility. We attribute the wide range of UF's to spatial factors in the distribution of light among the various sources. Keywords: Traffic Signals, Energy Efficiency, Usability Factors, Flicker Photometry, LED, Human Factors

The high incidence of accidents associated with work zones suggests that current warning lights and signals have been in need of improvement. In this project we have developed and tested an improved emergency warning light intended specifically for Caltrans work zone vehicles, and an enhanced rear warning light for shadow trucks, both intended to improve visibility and conspicuity, and to reduce reaction times for drivers approaching the work zone.