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The Public Right-of-Way Accessibility Guidelines (PROWAG) rulemaking has concluded. The PROWAG final rule has been published in the Federal Register. Please visit the Access Board’s PROWAG page for the guidelines.

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

MUTCD 2000: Manual on Uniform Traffic Control Devices Millennium Edition. (2000). U.S. DOT Federal Highway Administration.

The following sections were excerpted from the electronic version of the MUTCD Millennium Edition, which can be found at the Federal Highway Administration’s web site at With the exception of formatting and some minor additions (in italics), nothing was changed.

MUTCD Definition of Changeable Message Signs — signs that are capable of displaying more than one message, changeable manually, by remote control, or by automatic control. These signs are referred to as Dynamic Message Signs in the National Intelligent Transportation Systems (ITS) Architecture.

The MUTCD has general guidance for changeable (or dynamic) message signs which is found in Section 2A.07 and 6F.52. The FHWA has approved experimentation projects to study the operational and safety affects of certain dynamic message signs. For example, approval has been given to Maine DOT to experiment with a dynamic message sign under experimental request no. II-409 (Ex) and approval was also given to Virginia DOT under experimental request no. II-261 (Ex) to evaluate an Intersection Collision Countermeasure System that incorporates dynamic message signs. Our goal is to gather enough evaluation data to help determine future dynamic message sign standards for the MUTCD.

Section 2A.07 Changeable Message Signs

Standard: Changeable message signs, which are traffic control devices designed to display variable messages, shall conform to the principles established in this Manual, and to the extent practical, with the design and applications prescribed in Sections 6F.52 and 6F.55.

Guidance: Changeable message signs should not be used to display information other than regulatory, warning, and guidance information related to traffic control.

Support: Changeable message signs, with more sophisticated technologies, are gaining widespread use to inform road users of variable situations, particularly along congested traffic corridors. Highway and transportation organizations are encouraged to develop and experiment (see Section 1A.10) with changeable message signs and to carefully evaluate such installations so that additional standards may be adopted in the future. Information regarding the design and application of portable changeable message signs in temporary traffic control zones is contained in Section 6F.52.

Section 6F.52 Portable Changeable Message Signs

Standard:Portable Changeable Message signs shall be temporary traffic control devices with the flexibility to display a variety of messages. Each message shall consist of either one or two phases. Typically, a phase shall consist of up to three lines of eight characters per line.

Support: Portable Changeable Message signs are used most frequently on high-density urban freeways, but have applications on all types of highways where highway alignment, road user routing problems, or other pertinent conditions require advance warning and information.

Guidance: The components of a Portable Changeable Message sign should include: a message sign panel, control systems, a power source, and mounting and transporting equipment. Portable Changeable Message signs should subscribe to the principles established in this Manual and, to the extent practical, with the design (that is, color, letter size and shape, and borders) and applications prescribed in this Manual, except that the reverse colors for the letters and the background are considered acceptable. The front face of the sign should be covered with a protective material. The color of the elements should be yellow or orange on a black background.

Option: The message sign panel may vary in size.

Standard: Portable Changeable Message signs shall automatically adjust their brightness under varying light conditions, to maintain legibility. The control system shall include a display screen upon which messages can be reviewed before being displayed on the message sign. The control system shall be capable of maintaining memory when power is unavailable. Portable Changeable Message signs shall be equipped with a power source and a battery back-up to provide continuous operation when failure of the primary power source occurs. The mounting of Portable Changeable Message signs shall be such that the bottom of the message sign panel shall be a minimum of 2.1 m (7 ft) above the roadway when it is in the operating mode. The text of the messages shall not scroll or travel horizontally or vertically across the face of the sign.

Support: Portable Changeable Message signs have a wide variety of applications in temporary traffic control zones including: roadway, lane, or ramp closures, crash or emergency incident management, width restriction information, speed reductions, advisories on work scheduling, road user management and diversion, warning of adverse conditions, and operation control.

Guidance: Portable Changeable Message signs should be used as a supplement to and not as a substitute for conventional signs and pavement markings.

Support: The primary purpose of Portable Changeable Message signs in temporary traffic control zones is to advise the road user of unexpected situations. Some typical applications include the following:

  1. Where the speed of motor vehicle traffic is expected to drop substantially;
  2. Where significant queuing and delays are expected;
  3. Where adverse environmental conditions are present;
  4. Where there are changes in alignment or surface conditions;
  5. Where advance notice of ramp, lane, or roadway closures is needed;
  6. Where crash or incident management is needed; and/or
  7. Where changes in the road user pattern occur.

Guidance: When Portable Changeable Message signs are used for route diversion, they should be placed far enough in advance of the diversion to allow road users ample opportunity to exit the affected highway. The Portable Changeable Message signs should be sited and aligned to ensure legibility. Multiple Portable Changeable Message signs should be placed on the same side of the roadway, separated from each other at distances based on Table 6C-1. Portable Changeable Message signs should be placed on the shoulder of the roadway or, if practical, further from the traveled lane. They should be delineated with retroreflective temporary traffic control devices or when within the clear zone, shielded with a barrier or crash cushion. When Portable Changeable Message signs are not being used, they should be removed; if not removed, they should be shielded; or if the previous two options are not feasible, they should be delineated with retroreflective temporary traffic control devices. Portable Changeable Message sign trailers should be delineated on a permanent basis by affixing retroreflective material, known as conspicuity material, in a continuous line on the face of the trailer as seen by oncoming road users.

Messages should be designed taking into account the following factors:

  1. Each phase should convey a single thought.
  2. If the message can be displayed in one phase, the top line should present the problem, the centerline should present the location or distance ahead, and the bottom line should present the recommended driver action.
  3. The message should be as brief as possible.
  4. When a message is longer than two phases, additional Portable Changeable Message signs should be used.
  5. When abbreviations are used, they should be easily understood (see Section 1A.14).

Section 1A.14 Abbreviations Used on Traffic Control Devices (including VMS)

Standard: When abbreviations are needed for traffic control devices, the abbreviations shown in Table 1A-1 shall be used.

Guidance:The abbreviations for the words listed in Table 1A-2 should not be used in connection with traffic control devices unless the prompt word shown in Table 1A-2 either precedes or follows the abbreviation.

Standard: The abbreviations shown in Table 1A-3 shall not be used in connection with traffic control device because of their potential to be misinterpreted by road users.

Table 1A-1.** Acceptable Abbreviations

Word Message: Standard Abbreviation

  • Afternoon/Evening: PM
  • Alternate:ALT
  • Avenue:AVE
  • Bicycle: BIKE
  • Boulevard: BLVD
  • Cannot: CANT
  • CB Radio: CB
  • Center CNTR
  • Civil Defense: CD
  • Compressed Natural Gas: CNG
  • Crossing (other than highway-rail): XING
  • Diesel Fuel: D
  • Do Not: DONT
  • Drive: DR
  • East: E
  • Eastbound: EB
  • Electric Vehicle: EV
  • Emergency: EMER
  • Entrance, Enter: ENT
  • Expressway: EXPWY
  • Feet: FT
  • FM Radio: FM
  • Freeway: FRWY, FWY
  • Friday: FRI
  • Hazardous Material: HAZMAT
  • High Occupancy Vehicle: HOV
  • Highway: HWY
  • Rail Grade Crossing Pavement Marking: RXR
  • Hospital: H
  • Hour(s): HR
  • Information: INFO
  • It Is: ITS
  • Junction / Intersection: JCT
  • Kilogram: kg
  • Kilometer(s): KM
  • KilometersPer Hour: km/h
  • Lane: LN
  • Left:LFT
  • Liquid Propane Gas: LP-GAS
  • Maintenance: MAINT
  • Meter(s): M
  • Metric Ton: t
  • Mile(s): MI
  • MilesPer Hour: MPH or M.P.H.
  • Minute(s): MIN
  • Monday: MON
  • Morning/ Late Night: AM
  • Normal: NORM
  • North: N
  • Northbound: NB
  • Parking: PKING
  • Pedestrian: PED
  • Pounds: LBS
  • Right: RHT
  • Road RD
  • Saturday: SAT
  • Service: SERV
  • Shoulder: SHLDR
  • Slippery: SLIP
  • South: S
  • Southbound: SB
  • Speed: SPD
  • Street: ST
  • Sunday: SUN
  • Telephone: PHONE
  • Temporary: TEMP
  • Thursday: THURS
  • TiresWith Lugs: LUGS
  • Tons of Weight: T
  • Traffic: TRAF
  • Travelers: TRAVLRS
  • Tuesday: TUES
  • Two-Way Intersection: 2-WAY
  • Two-Wheeled Vehicles: CYCLES
  • US Numbered Route: US
  • Vehicles: VEH
  • Warning: WARN
  • Wednesday: WED
  • West: W
  • Westbound: WB
  • Will Not: WONT

Table 1A-2. Abbreviations That Are Acceptable Only with a Prompt Word

Word Message Word/ Abbreviation/ Prompt Word

*These prompt words should precede the abbreviation

  • Access/ ACCS/ Road
  • Ahead/ AHD/ Fog*
  • Blocked/ BLKD/ Lane*
  • Bridge/ BRDG/ [Name]*
  • Condition/ COND/ Traffic*
  • Congested/CONG/Traffic*
  • Construction/ CONST/ Ahead
  • Downtown/ DWNTN/Traffic*
  • Eastbound/ E-BND/ Traffic
  • Exit/ EX, EXT/ Next*
  • Express/ EXP/ Lane
  • Frontage/ FRNTG/ Road
  • Hazardous/ HAZ/ Driving
  • Interstate/ I/[Number]
  • Local/LOC/Traffic
  • Lower/ LWR/ Level
  • Major/ MAJ /Accident
  • Minor/ MNR/ Accident
  • Northbound/N-BND/ Traffic
  • Oversized/ OVRSZ/Load
  • Prepare/PREP/To Stop
  • Pavement/ PVMT/Wet*
  • Quality/ QLTY/ Air*
  • Roadwork/ RDWK/ Ahead [Distance]
  • Route/ RT/Best*
  • Southbound/ S-BND/Traffic
  • Township/ TWNSHP/Limits
  • Turnpike/ TRNPK/[Name]*
  • Upper/ UPR/Level
  • Vehicle/ VEH/Stalled*
  • Westbound/W-BND/Traffic

Table 1A-3.Unacceptable Abbreviations

Abbreviation/ Intended Word/ Common Misinterpretations

  • ACC/Accident/Access (Road)
  • CLRS/Clears/Colors
  • DLY/Delay/Daily
  • FDR/Feeder/Federal
  • L/Left Lane/ (Merge)
  • LT/ Light (Traffic)/Left
  • PARK/Parking/Park
  • POLL/Pollution (Index)/ Poll
  • RED/ Reduce/Red
  • STAD/Stadium/Standard
  • WRNG/Warning/Wrong

The following are from the ADA Accessibility Guidelines for Transportation Vehicles and ADA Standards for Accessible Design. These standards do not directly address VMS or electronic signs in general, but are applied to all signage applications (including VMS) in and on transportation vehicles and in public and commercial facilities. Sections were omitted that did not pertain to sign visibility.

AmericansWith Disabilities Act (ADA) Accessibility Guidelines for Transportation Vehicles Part, 1192

§1192.39 Destination and route signs.

(a) Where destination or route information is displayed on the exterior of a vehicle, each vehicle shall have illuminated signs on the front and boarding side of the vehicle.

(b) Characters on signs required by paragraph (a) of this section shall have a width-to-height ratio between 3:5 and 1:1 and a stroke width-to-height ratio between 1:5 and 1:10, with a minimum character height (using an upper case “X”) of 1 inch for signs on the boarding side and a minimum character height of 2 inches for front “headsigns”, with “wide” spacing (generally, the space between letters shall be 1/16 the height of upper case letters), and shall contrast with the background, either dark-on-light or light-on-dark.

Nondiscrimination on the basis of disability by public accommodations and in commercial facilities (1994). ADA Standards for Accessible Design.Pt. 36 Department of Justice 28 CFR Part 36.

4.30 Signage.

4.30.2 Character Proportion. Letters and numbers on signs shall have a width-to-height ratio between 3:5 and 1:1 and a stroke-width-to- height ratio between 1:5 and 1:10.

4.30.3 Character Height. Characters and numbers on signs shall be sized according to the viewing distance from which they are to be read. The minimum height is measured using an upper case X. Lower case characters are permitted. Minimum character height 3 in (75 mm).

Characters and symbols shall contrast with their background –either light characters on a dark background or dark characters on a light background.

The following guidelines and standards are appended from: Wourms, Cunningham, Self, and Johnson, 2001. Bus signage guidelines for persons with visual impairments: electronic signs. Federal Transit Administration Report FTA-VA-26-7026-02.1.

American Public Transit Association (APTA) Guidelines

The Standard Bus Procurement Guidelines (SBPG) issued by APTA are a model for solicitation of offers and contracts for the supply of transit buses. They are intended to be a starting point for a transit agency assembling a solicitation of offers and to assist in a cost-effective procurement. SBPG Part 5: Technical Specifications defines requirements for a heavy duty transit bus which, by the selection of specifically identified alternative configurations, may be used for both suburban express service and general service on urban arterial streets. It is intended for the widest possible spectrum of passengers, including children, adults, the elderly, and persons with disabilities. The destination sign design guidelines offered within Part 5 of the SBPG document are as follows (emphasis added):

I. An automatic electronic destination sign system shall be furnished on the front, on the right side near the front door, and on the rear of the vehicle. Display areas of destination signs shall be clearly visible in direct sunlight and/or at night. The sign system shall provide optimum visibility of the message display units for passengers and shall meet applicable **ADA requirements defined in 49 CFR, Part 38.39.

II.The front destination sign shall have no less than 1,689 octagonal dot pixels, 16 rows by 105 columns, with a message display area of not less than 9.8 inches high by not less than 63 inches wide.

III.The side destination sign shall have no less than 672 octagonal dot pixels, having at least 8 rows and 84 columns with a message display area of not less than 3.15 inches high by not less than 30 inches wide.

IV.The rear route number sign display area shall have no less than 448 octagonal dot pixels, having at least 8 rows and 28 columns with a message display area of not less than 6.1 inches high by not less than 11 inches wide.

V. Sign displays shall have alternating message capability with programmable blanking time between message lines as may be required. Variable blanking times shall be programmable between 0.5 to 25 seconds in duration.

Transportation Research Board, Transit Cooperative Research Program (TCRP)

The TCRP, proposed by the U. S. Department of Transportation (DOT), authorized as part of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), and established under FTA sponsorship in July 1992, serves as one of the principal means by which the transit industry can develop innovative near-term solutions to meet the demands of upgrading transit systems, expanding service areas, increasing service frequency, and improving transit system efficiency.

The TCRP provides a forum where transit agencies can cooperatively address common operational problems and support and complement other ongoing transit research and training programs. The next sections provide excerpts from two TCRP reports containing relevant transit signage guidelines and recommendations.

Guidelines for Transit Facility Signing and Graphics—TCRP Report 12

This report was designed to assist transit operators in the use of appropriate signs and symbols for their facilities. These guidelines describe the use of signs and symbols that provide for the safe and efficient movement of passengers to and through transit facilities. These guidelines also assist transit operators in providing passenger information systems that encourage the use of transit by new users, infrequent riders, and individuals with disabilities.

While not specific to destination signage, a section of the report devoted to electronic visual information displays describes the characteristics of LED displays (LED size, dot pitch, character formation, and display luminance) that affect their performance as follows (emphasis added):

I.LED Size—The diameter (or width if the display is a matrix of square LED elements) of one LED is referred to as the “dot size” of the display. The prevalent dot size for transit system displays is currently 5 mm (0.197 in.).

II.Dot Pitch—The** dot pitch, or distance between dot centers, which is currently prevalent in transit system displays is 6 mm (.236 in.). Greater spacing between dots produces a reduction in readability. This is due to the loss of a cumulative effect whereby adjacent LEDs act together to form an image, rather than as individual dots.

III.Character Formation—To form a character, a minimum dot matrix of 7 x 9 is preferred. Characters must be double stroke (made up of two adjacent rows of dots).

Display Luminance—The display must be capable of enough brightness to be visible in the intended environment. If lighting conditions are variable, this would make the display too bright for the lower illumination levels. Therefore, dimming controls or sensors should be used for displays with varied ambient conditions. Current indoor, semi-outdoor, and ultra bright versions of LED blocks for different illumination levels are available.

Passenger Information Services: A Guidebook for Transit Systems—TCRP Report 45

The objective of this report is to produce a clear and practical guidebook to assist transit professionals in making transit information more accessible and user friendly for transit systems of varying complexity. The guidelines include a compilation of principles for the design and format details that are part of all passenger information aids. This research did not develop a high-technology, paperless approach to passenger information. Rather, it focused on traditional media for presentation of information, such as schedules, maps, and signage. Therefore, this section first offers recommendations specific to traditional bus header/identifications signs. It then presents general recommendations and guidelines to help make transit information systems easier to read and understand.

I.A* bus header/identification sign is mounted on the bus front* (at least; rear and sides if possible) in static or electronic form, to identify the route number and name (if any) and, if applicable, the direction in which the bus is traveling. The sign should be visible to passengers waiting at the bus stop.

II.Route number must be legible to persons with low vision (20/200), in daylight conditions, at 30 feet *(i.e., six inch high characters and/or symbols, preferably larger*).

III.Placementshould be* high on the bus body, above the window lin*e.

IV.Display may be by changeable message sign. Back illumination or flood illumination should be provided for nighttime operations.

For general application to transit industry information systems, the following suggestions apply:

I.Use all capital letters (upper case)for stop designations, terminals, and other short labels.

II.Usecapital and lower case letters for long legends and instructions.

Given that viewing distances for signs will vary according to where they are placed in relation to the intended reader, this guidebook specifies most sign character sizes in terms of visual angle. This is expressed either in degrees or in radians. The visual angle is the angle that the letter or other object makes up in the visual field of the reader. A person with “normal” vision (20/20) will just be able to make out letters that are 1/12 degrees(0.00145 radian) of arc. ADA requirements call for the major route designators and other essential information to be visible from 30 feet away by individuals with low vision. This translates into a requirement for approximately 1 degree letters(0.017 radian

For signs and printed materials that are not black-on-white (especially for bus stop signs, which may be a unique color for visibility against other street signs), a contrast formula can help determine how well text or other elements will stand out against a background. Contrast for all signs, schedules, and publications should be at least 70 percent.

The Public Service Vehicle Accessibility Regulations 2000

This United Kingdom document is intended to provide guidance for those in the manufacturing and operating industries. The Public Service Vehicles Accessibility Regulations 2000 prescribe the minimum acceptable to meet the needs of people with disabilities. The guidance explains the intention of the regulatory requirements and provides advice on best practice that should be followed, recognizing that there may be circumstances in which design or operational constraints apply.

A regulated public service vehicle shall be fitted with a route number display and a destination display in the following positions:

I. On the front of the vehicle, as close as practicable to the part of the windscreen which is within the driver’s field of vision; and

II.On the near-side of the vehicle adjacent to the entrance which is closest to the front of the vehicle at a height of not less than 1.2 meters to the lower edge of the display characters and not more than 2.5 meters to the upper edge of the display characters measured from the ground and, if fitted with a kneeling system, with the vehicle in the normal condition for vehicle travel.

III.The front display may be fitted above the windscreen or, as low as practicable within the windscreen area, but above the driver’s field of view. It must not be placed in any position that may obscure the driver’s field of view.

IV.A regulated public service vehicle shall be fitted with a route number display on the rear of the vehicle.

Any route number display shall be capable of displaying the following:

I. Characters of not less than 200mm in height on the front and rear of the vehicle and not less than 70mm in height on the side of the vehicle,

II.Characters that contrast with the display background,

III.Characters that are provided with a means of illumination, and

IV.Not less than three characters.

Any destination display shall be capable of displaying the following:

I.Characters of not less than 125mm in height when fitted to the front of a vehicle and not less than 70mm in height when fitted to the side of a vehicle,

II.Characters that contrast with the display background,

III.Characters that are provided with a means of illumination,

IV.Not less than fifteen characters, and

V.White or bright yellow lettering on a black background is most clearly visible.

VI.LED/LCD or other electronically generated characters should only be used if they can offer the same clarity, both night and day, as a conventional roller blind display.

VII. Destination information shall not be written in capital letters only. The use of both upper and lower case text helps ensure that words that are not completely clear and legible to people with a degree of vision impairment or learning disability, are still identifiable through shape recognition of the word.