Synthesis on the Legibility of Variable Message Signing (VMS) For Readers With Vision Loss: Executive Summary
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 dramaticallyo ver 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.
The US Census Bureau (1997) reported that 3.7% of U.S. citizens (7.7 million people) over 15 years of age “had difficulty seeing words/letters,” this jumps to 12.1% for individuals 65 years of age and older. Based on National Center for Health Statistics data it has been estimated that in the United States there are “6.6 million people unable to read printed signs at normal viewing distances.”
The goal of this research project was to gather and synthesize existing information on the legibility of VMS for people with visual impairments with the intent of identifying the features of current and prospective VMS technology that can be improved to better serve the needs of this user group. 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 However, as publication of research results often takes several years and as much research goes unpublished, a request for information was sent to the Human Factors and Ergonomics Society’s “Surface Transportation” and “Perception and Performance” Technical Groups’ listservs. Messages sent to these listservs go out to nearly 500 professionals in fields related to this research project.
The 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 provides 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 advantages, disadvantages, and use in transit facilities. Two sections are appended to the end of the document. Appendix A contains a detailed bibliography with citations and abstracts. These are divided into two sections: Transportation VMSResearch, and Electronic Text Readability for Individual with Vision Impairments. Appendix B contains an annotated bibliography of state, national, and international VMS design and implementation guidelines and standards.
The research conducted for this report identified the existence of certain design criteria that, if met, will be capable of significantly improving the legibility of VMS for a large percentage of individuals with vision impairments. The question is, are the current findings sufficiently robust to be used to make solid recommendations. In a very recent synthesis on LED/LCD VMS for use on transit vehicles conducted for the Federal Transit Administration (FTA), it was concluded that there was sufficient available guidance on several indices, including: the position of on-vehicle VMS; character height; width-to-height ratio; stroke width-to-height ratio; and inter-character spacing. Conversely, the FTA study stated that there were insufficient data regarding: visibility under varying lighting conditions; streaming and paging style and rate; sign color; relative motion between the sign and the observer; and glare effects.
The present report supports the FTA study conclusions regarding the need for further research to fill the gaps they identified, particularly with regard to paging and streaming rates and time allotted for individuals with vision impairments to read VMS. This report however demonstrates that other issues (e.g., letter height, color, and luminance), alone and in combination, may still benefit from additional study. In particular, appropriate letter heights should be developed using new, brighter light emitting VMS, in combination with streaming text for subjects who have a variety of functional visual impairments (e.g., scotoma, CFL, and PFL). Furthermore, the use of an analytical model to determine letter heights (as suggested in the FTA research and elsewhere) does not address the complexity of VMS reading by individuals with vision impairments in real-world environments. A summary of recommendations regarding the application of current knowledge to future VMS design, and recommendations for future research to fill the gaps in that current knowledge can be found in Table 1.
Table 1.Recommended values for VMS characteristics; issues and future research needs. (Text Version)
| VMS Characteristic | Recommended | Issues and Future Research |
| Letter Height for VMS on Vehicles | Not less than 10 inch | – VMS legibility distance for 8inch letters has been found to be less than 20 feet for people with 20/80 to 20/160 acuity. |
| – Research should be conducted to determine what letter height will optimize reading speed and legibility distance for individuals with vision impairments reading dynamic messages. | |||
| Letter Height for VMS in Facilities | Not less than 6 inch | ||
| Width to Height Ratio | 0.7 to 1.0 | – Existing research on this variable is fairly strong and, at a minimum, supports the use of 5x7 versus a 4x7 character matrix. | |
| Stroke Width to Height Ratio | 0.2 | – Existing research on this variable is fairly strong and supports the use of a 1:5 ratio. | |
| Text Color | Green or Yellow | – Existing research indicates that these two colors provide the best legibility for readers with vision impairments. |
| – Additional research should be conducted to determine if other colors now available in high brightness LEDs provide any benefit to individuals with vision impairments. | ||
| Font | 5x7 for Uppercase |
| 7x9 for Lowercase | – Existing research on this variable is fairly strong. | |
| Luminance | Night: 30cd/m2 |
| Day: >1,000cd/m2 | – Existing research on this variable is fairly strong for individuals without vision impairments. |
– Additional research should be conducted to determine if these levels are sufficient for individuals with vision impairments.
| – European standards currently under development should be tracked to determine measurement methods/recommended levels. | |||
| Luminance Contrast | (Lt-Lb)/Lb = 8 to 12 | –Existing research on this variable is strong for individuals without vision impairments. |
| –Research should be conducted to determine if these levels are sufficient for individuals with vision impairments. | ||
| Inter character Spacing | 25 to 40% |
| letter height | – Existing research on this variable is strong. | |
| Inter word spacing | 75-100% |
| letter height | – Existing research on this variable is strong. | |
| Inter line spacing | 50 to 75% |
| letter height | – Existing research on this variable is strong. | ||
| Case | Uppercase or mixed case for single words | – Existing research on this variable is strong; however attaining high-quality lowercase letterforms using a matrix format is difficult. If this cannot be attained, uppercase letters is preferable. | |
| Lowercase for longer textual messages | |||
| Contrast Orientation | Positive | – Existing research on this variable is strong for individuals without vision impairments. |
| – Research is needed to determine if the findings apply to individuals with vision impairments. | |||
| Sign Width | Dynamic text should be capable of displaying 6-7 characters | – Additional research on this variable should be conducted to determine if this basic research finding holds up in real-world VMS reading by individuals with vision impairments. | |
| Paging or Streaming | Streaming | – Additional research should be conducted. | |
| Static Display Time | 10 Seconds | – This is a very weak recommendation and very much in dispute. |
| – Additional research must be conducted to determine appropriate reading times for sign comprehension by individuals with vision impairments. |
