Table 2. Recommended values for VMS characteristics, issues, and future research needs.

VMS Characteristic: Letter Height for VMS on Vehicles
Recommended Values: Not less than 10 inch
(will allow for 30 ft legibility distance at an LI* of 3 ft/in)

VMS Characteristic: Letter Height for VMS in Facilities
Recommended Values: Not less than 6 inch
(will allow for 18 ft legibility distance at an LI of 3 ft/in)
Issues and Future Research: -- Using 8-inch letters, Bentzen, et. al. (1994) found mean VMS
legibility distance to be less than 20 feet for subjects 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.


VMS Characteristic: Width to Height Ratio
Recommended Values: 0.7 to 1.0

Issues and Future Research: 
-- Existing research on this variable is fairly strong and, at a minimum, supports the use of 5x7
versus a 4x7 character matrix.
VMS Characteristic: Stroke Width to Height Ratio
Recommended Values: 0.2

Issues and Future Research: 
-- Existing research on this variable is fairly strong and supports the use of a 1:5 ratio.
VMS Characteristic: Text Color
Recommended Values: Green or Yellow

Issues and Future Research: 
-- 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 the visually impaired.
VMS Characteristic: Font
Recommended Values: 5x7 for Uppercase
7x9 for Lowercase

Issues and Future Research: 
-- Existing research on this variable is fairly strong.

VMS Characteristic: Luminance
Recommended Values: Night: 30cd/m2
Day: >1,000cd/m2
Issues and Future Research: 
-- 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.
-- New European standards currently under development should be tracked to determine
measurement methods and recommended levels.

VMS Characteristic: Luminance Contrast
Recommended Values: (Lt-Lb)/Lb = 8 to 12
Issues and Future Research: 
-- 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.

VMS Characteristic: Inter character Spacing
Recommended Values: 25 to 40% letter height
Issues and Future Research: 
-- Existing research on this variable is strong.

VMS Characteristic: Inter word spacing
Recommended Values: 75-100% letter height
Issues and Future Research: 
-- Existing research on this variable is strong.

VMS Characteristic: Inter line spacing
Recommended Values: 50 to 75% letter height
Issues and Future Research: 
-- Existing research on this variable is strong.

VMS Characteristic: Case
Recommended Values: Uppercase or mixed case for single words
Lowercase for longer textual messages
Issues and Future Research: 
-- Existing research on this variable is strong; however attaining high-quality lowercase
letterforms using a matrix format is difficult. If this cannot be attained, then all uppercase letters
is preferable.

VMS Characteristic: Contrast Orientation
Recommended Values: Positive
Issues and Future Research: 
-- Existing research on this variable is strong for individuals without vision impairments.
-- Research should be conducted to determine if the findings are the same for individuals with
vision impairments.

VMS Characteristic: Sign Width
Recommended Values: Dynamic text should be capable of displaying 6-7 characters
Issues and Future Research: 
-- 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
Recommended Values: Streaming
VMS Characteristic: Static Display Time
Recommended Values: 10 Seconds
Issues and Future Research: 
-- This is a very weak recommendation and very much in dispute.
-- Additional research must be conducted to determine the appropriate reading time needed for
sign comprehension by individuals with vision impairments.

VMS Characteristic: Streaming RateRecommended Values: 2.74 seconds per frame dwell time
Issues and Future Research: 
-- This is a very weak recommendation as it is based on a single research study (Bentzen and
Easton, 1996).
-- Additional research must be conducted to determine the appropriate streaming rate individuals
with vision impairments.