Driver Understanding of Messages Displayed on Sequential Portable Changeable Message Signs in Work Zones

In this paper, researchers present the results of a Texas Transportation Institute (TTI) driving simulator study of the ability of motorists to capture and process information on two portable changeable message signs (PCMSs) used in sequence (i.e., one PCMS following another along the edge of the roadway such that each PCMS contains part of a single message) to convey information about upcoming traffic situations. The study results indicate the need to keep overall messages at or below the four-unit maximum recommended in existing guidelines. Researchers found that presenting five units of information on sequential PCMSs resulted in low comprehension rates, below what would be acceptable for highway applications. However, by keeping the message length to four units, it does appear that the use of sequential PCMSs will result in comprehension rates comparable to those obtained by presenting the same information at a single location on a large dynamic message sign (DMS). Comprehension may be enhanced by repeating one of the lines of the message on both PCMSs used in sequence.