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Synthesis on the Legibility of Variable Message Signing (VMS) for Readers with Vision Loss

May 14, 2002 Philip M. Garvey The Pennsylvania Transportation Institute The Pennsylvania State University University Park, PA 16802


The use of electronic variable message signs (VMS) to provide traveler information at airports, transit stations, on transit vehicles, along highways, and for pedestrian and driver signaling has increased dramatically over the past 20 years. The accurate and often real-time information that these devices furnish to travelers in highway and transit environments has made substantial improvements to human centered transportation in the late 20th and early part of the 21st century. However, while much is known about optimizing VMS legibility for people with “normal” vision, and about the legibility of printed text for people who have partial sight, there are still no standards that ensure VMS legibility for either the general population of travelers or for those with visual impairments.

In the early to mid 1990’s there were a large number of Federally funded research projects aimed at assessing VMS legibility and developing guidelines for their use (e.g., Dudek, 1991, 1997; Upchurch, Armstrong, Baaj, and Thomas, 1992; Bentzen, Easton, Nolin, and Mitchel, 1994; Bentzen and Easton 1996; and Garvey and Mace, 1996). Dudek (1997) synthesized much of the highway research for the National Cooperative Highway Research Program (NCHRP) and the findings directly related to the legibility of transit VMS for individuals with vision impairments were summarized by Hunter-Zaworski (1994) for the Federal Transit Administration (FTA). While much of this research is still valid, due to recent advances in VMS technology a good deal of it is no longer current.


The goal of this research project was to gather and synthesize existing information on the legibility of VMS for pple with visual impairments with the intent of identifying the features of current and prospective VMS technology that can be improved to better serve the needseo of this user group.

Satisfying Objectives


Unfortunately, most VMS legibility research has been conducted in the highway environment where visual impairment is kept to a minimum by licensure restrictions. Of course, once a driver has a license their vision is rarely retested. There are, therefore, many drivers with visual impairments that have occurred since their initial licensure. Nominally, however, licensed U.S. drivers have high contrast distance visual acuity of 20/40 or better and, because of this restriction, the Federal Highway Administration (FHWA) only requires signs to accommodate relatively high visually functioning individuals.

This is typically not seen as a problem. As vision plays such a large role in driving, the general consensus is that high standards of visual performance are desirable. However, as a result research on highway VMS does not include a visually impaired component. While it is true that most human factors research conducted on highway VMS in the past decade has involved older drivers as subjects to account for age-related losses in vision (e.g., Garvey and Mace, 1996; Upchurch, et al., 1992), the recommendations still do not go beyond visual acuities of about 20/50 and never approach the type or extent of visual impairments that are found in other VMS reading environments such as transit.

Overcoming Obstacles

Despite these limitations, research conducted in the highway environment withnon visually impaired observers can still be used to describe VMS characteristics that contribute to legibility for all readers, regardless of their visual abilities (e.g., increasing letter height and luminance contrast will help almost everybody). However, to accomplish the specific goal of synthesizing VMS legibility requirements for readers with vision impairments, the literature review conducted for this report had to go beyond the evaluation of transportation research to include the more basic visual impairment research being conducted in the fields of psychology, ophthalmology, and psycholinguistics.

To realize the project objectives, an extensive literature search was conducted using the Transportation Research Board’s (TRB) Transportation Research Information Services (TRIS), WinSpirs-TRANSPORT transportation literature database, and PsycINFO (via SilverPlatter) using Pennsylvania State University’s LIAS system. However, as publication of research results often takes several years and as much research goes unpublished, the current knowledge in any field is in the minds and hands of the people working in that field. Therefore, a request for information regarding this topic was sent to the Human Factors and Ergonomics Society’s “Surface Transportation” and “Perception and Performance” Technical Groups’ listservs. Messages sent to these listservs are received by nearly 500 professionals in fields related to this research project.

Note on Usage

With the Millennium edition of the Manual on Uniform Traffic Control Devices (MUTCD, 2000), the highway community officially adopted the term Changeable Message Signs (CMS) for the type of signs researched in this report. The transit community mainly calls these devices Variable Message Signs (VMS) but also uses Passenger (or Customer) Information Systems and Passenger Information Displays, while the intelligent transportation systems (ITS) community commonly uses the term Dynamic Message Signs (DMS). For the purposes of continuity, the term VMS will be used throughout this report unless another source is quoted.

Report Strategy

The remainder of this report begins with a discussion of common visual impairments and how they might affect an individual’s ability to read VMS. This is followed by a detailed review of research on the legibility of VMS in highway and transit applications, and the readability of electronic copy (VMS and non-VMS) for individuals with vision impairments. The final section of this report is an overview of VMS technologies currently used in transit and the highway environment. A brief description of each technology is accompanied by a discussion of their advantages, disadvantages, and use in transit facilities. The scope of the project did not allow for a survey of transit authorities to be conducted, therefore the VMS transit applications were obtained from the literature review. Because of delay in publishing, statements regarding transit authorities’ use of VMS will mainly reflect usage in the mid to late 1990’s, with a small number of references to the early part of the 21st century.

Two sections are appended to the end of the text document. Appendix A contains a detailed bibliography with citations and abstracts. These citations are divided into two sections: Transportation VMS Research, And Electronic Text Readability for Individuals with Vision Impairments. Appendix B contains an annotated bibliography of state, national, and international VMS design and implementation guidelines and draft standards.