Manual on Road Traffic Engineering Facilities

道路交通工程设施设置指南

Sign

Section 2A.01 Function and Purpose of Signs

Support:
01 This Manual contains Standards, Guidance, and Options for the signing of all types of highways, and private roads open to public travel. The functions of signs are to provide regulations, warnings, and guidance information for road users. Words, symbols, and arrows are used to convey the messages. Signs are not typically used to confirm rules of the road.

02 Detailed sign requirements are located in the following Chapters of Part 2:

Standard:
03 Because the requirements and standards for signs depend on the particular type of highway upon which they are to be used, the definitions for freeway, expressway, conventional road, and special purpose road given in Section 1A.13 shall apply in Part 2.

Section 2A.02 Definitions

Support:
01 Definitions and acronyms that are applicable to signs are given in Sections 1A.13 and 1A.14.

Section 2A.03 Standardization of Application

Support:
01 It is recognized that urban traffic conditions differ from those in rural environments, and in many instances signs are applied and located differently. Where pertinent and practical, this Manual sets forth separate recommendations for urban and rural conditions.

Guidance:
02 Signs should be used only where justified by engineering judgment or studies, as provided in Section 1A.09.

03 Results from traffic engineering studies of physical and traffic factors should indicate the locations where signs are deemed necessary or desirable.

04 Roadway geometric design and sign application should be coordinated so that signing can be effectively placed to give the road user any necessary regulatory, warning, guidance, and other information.

Standard:
05 Each standard sign shall be displayed only for the specific purpose as prescribed in this Manual. Determination of the particular signs to be applied to a specific condition shall be made in accordance with the provisions set forth in Part 2. Before any new highway, private road open to public travel (see definition in Section 1A.13), detour, or temporary route is opened to public travel, all necessary signs shall be in place. Signs required by road conditions or restrictions shall be removed when those conditions cease to exist or the restrictions are withdrawn.

Section 2A.04 Excessive Use of Signs

Guidance:
01 Regulatory and warning signs should be used conservatively because these signs, if used to excess, tend to lose their effectiveness. If used, route signs and directional guide signs should be used frequently because their use promotes efficient operations by keeping road users informed of their location.

Section 2A.05 Classification of Signs

Standard:
01 Signs shall be defined by their function as follows:

  1. Regulatory signs give notice of traffic laws or regulations.
  2. Warning signs give notice of a situation that might not be readily apparent.
  3. Guide signs show route designations, destinations, directions, distances, services, points of interest, and other geographical, recreational, or cultural information.

Support:
02 Object markers are defined in Section 2C.63.

Section 2A.06 Design of Signs

Support:
01 This Manual shows many typical standard signs and object markers approved for use on streets, highways, bikeways, and pedestrian crossings.

02 In the specifications for individual signs and object markers, the general appearance of the legend, color, and size are shown in the accompanying tables and illustrations, and are not always detailed in the text.

03 Detailed drawings of standard signs, object markers, alphabets, symbols, and arrows (see Figure 2D-2) are shown in the "Standard Highway Signs and Markings" book. Section 1A.11 contains information regarding how to obtain this publication.

04 The basic requirements of a sign are that it be legible to those for whom it is intended and that it be understandable in time to permit a proper response. Desirable attributes include:

  1. High visibility by day and night; and
  2. High legibility (adequately sized letters, symbols, or arrows, and a short legend for quick comprehension by a road user approaching a sign).

05 Standardized colors and shapes are specified so that the several classes of traffic signs can be promptly recognized. Simplicity and uniformity in design, position, and application are important.

Standard:
06 The term legend shall include all word messages and symbol and arrow designs that are intended to convey specific meanings.

07 Uniformity in design shall include shape, color, dimensions, legends, borders, and illumination or retroreflectivity.

08 Standardization of these designs does not preclude further improvement by minor changes in the proportion or orientation of symbols, width of borders, or layout of word messages, but all shapes and colors shall be as indicated.

09 All symbols shall be unmistakably similar to, or mirror images of, the adopted symbol signs, all of which are shown in the "Standard Highway Signs and Markings" book (see Section 1A.11). Symbols and colors shall not be modified unless otherwise provided in this Manual. All symbols and colors for signs not shown in the "Standard Highway Signs and Markings" book shall follow the procedures for experimentation and change described in Section 1A.10.

Option:
10 Although the standard design of symbol signs cannot be modified, the orientation of the symbol may be changed to better reflect the direction of travel, if appropriate.

Standard:
11 Where a standard word message is applicable, the wording shall be as provided in this Manual.

12 In situations where word messages are required other than those provided in this Manual, the signs shall be of the same shape and color as standard signs of the same functional type.

Option:
13 State and local highway agencies may develop special word message signs in situations where roadway conditions make it necessary to provide road users with additional regulatory, warning, or guidance information, such as when road users need to be notified of special regulations or warned about a situation that might not be readily apparent. Unlike colors that have not been assigned or symbols that have not been approved for signs, new word message signs may be used without the need for experimentation.

Standard:
14 Except as provided in Paragraph 16 and except for the Carpool Information (D12-2) sign (see Section 2I.11), Internet addresses and e-mail addresses, including domain names and uniform resource locators (URL), shall not be displayed on any sign, supplemental plaque, sign panel (including logo sign panels on Specific Service signs), or changeable message sign.

Guidance:
15 Unless otherwise provided in this Manual for a specific sign, and except as provided in Paragraph 16, telephone numbers of more than four characters should not be displayed on any sign, supplemental plaque, sign panel (including logo sign panels on specific service signs), or changeable message sign.

Option:
16 Internet addresses, e-mail addresses, or telephone numbers with more than four characters may be displayed on signs, supplemental plaques, sign panels, and changeable message signs that are intended for viewing only by pedestrians, bicyclists, occupants of parked vehicles, or drivers of vehicles on low-speed roadways where engineering judgment indicates that an area is available for drivers to stop out of the traffic flow to read the message.

Standard:
17 Pictographs (see definition in Section 1A.13) shall not be displayed on signs except as specifically provided in this Manual. Pictographs shall be simple, dignified, and devoid of any advertising. When used to represent a political jurisdiction (such as a State, county, or municipal corporation) the pictograph shall be the official designation adopted by the jurisdiction. When used to represent a college or university, the pictograph shall be the official seal adopted by the institution. Pictorial representations of university or college programs shall not be permitted to be displayed on a sign.

Section 2A.07 Retroreflectivity and Illumination

Support:
01 There are many materials currently available for retroreflection and various methods currently available for the illumination of signs and object markers. New materials and methods continue to emerge. New materials and methods can be used as long as the signs and object markers meet the standard requirements for color, both by day and by night.

Standard:
02 Regulatory, warning, and guide signs and object markers shall be retroreflective (see Section 2A.08) or illuminated to show the same shape and similar color by both day and night, unless otherwise provided in the text discussion in this Manual for a particular sign or group of signs.

03 The requirements for sign illumination shall not be considered to be satisfied by street or highway lighting.

Option:
04 Sign elements may be illuminated by the means shown in Table 2A-1.

Table 2A-1. Illumination of Sign Elements
Means of Illumination Sign Element To Be Illuminated
Light behind the sign face
  • Symbol or word message
  • Background
  • Symbol, word message, and background (through a translucent material)
Attached or independently mounted light source designed to direct essentially uniform illumination onto the sign face
  • Entire sign face
Light emitting diodes (LEDs)
  • Symbol or word message
  • Portions of the sign border
Other devices, or treatments that highlight the sign shape, color, or message:
Luminous tubing
Fiber optics
Incandescent light bulbs
Luminescent panels
  • Symbol or word message
  • Entire sign face

05 Retroreflection of sign elements may be accomplished by the means shown in Table 2A-2.

Table 2A-2. Retroreflection of Sign Elements
Means of Retroreflection Sign Element
Reflector "buttons" or similar units Symbol
Word message
Border
A material that has a smooth, sealed outer surface over a microstructure that reflects light Symbol
Word message
Border
Background

06 Light Emitting Diode (LED) units may be used individually within the legend or symbol of a sign and in the border of a sign, except for changeable message signs, to improve the conspicuity, increase the legibility of sign legends and borders, or provide a changeable message.

Standard:
07 Except as provided in Paragraphs 11 and 12, neither individual LEDs nor groups of LEDs shall be placed within the background area of a sign.

08 If used, the LEDs shall have a maximum diameter of 1/4 inch and shall be the following colors based on the type of sign:

  1. White or red, if used with STOP or YIELD signs.
  2. White, if used with regulatory signs other than STOP or YIELD signs.
  3. White or yellow, if used with warning signs.
  4. White, if used with guide signs.
  5. White, yellow, or orange, if used with temporary traffic control signs.
  6. White or yellow, if used with school area signs.

09 If flashed, all LED units shall flash simultaneously at a rate of more than 50 and less than 60 times per minute.

10 The uniformity of the sign design shall be maintained without any decrease in visibility, legibility, or driver comprehension during either daytime or nighttime conditions.

Option:
11 For STOP and YIELD signs, LEDs may be placed within the border or within one border width within the background of the sign.

12 For STOP/SLOW paddles (see Section 6E.03) used by flaggers and the STOP paddles (see Section 7D.05) used by adult crossing guards, individual LEDs or groups of LEDs may be used.

Support:
13 Other methods of enhancing the conspicuity of standard signs are described in Section 2A.15.

14 Information regarding the use of retroreflective material on the sign support is contained in Section 2A.21.

Section 2A.08 Maintaining Minimum Retroreflectivity

Support:
01 Retroreflectivity is one of several factors associated with maintaining nighttime sign visibility (see Section 2A.22).

Standard:
02 Public agencies or officials having jurisdiction shall use an assessment or management method that is designed to maintain sign retroreflectivity at or above the minimum levels in Table 2A-3.

Table 2A-3. Minimum Maintained Retroreflectivity Levels1
Sign Color Sheeting Type (ASTM D4956-04) Additional Criteria
Beaded Sheeting Prismatic Sheeting
I II III III, IV, VI, VII, VIII, IX, X
White on Green W*; G ≥ 7 W*; G ≥ 15 W*; G ≥ 25 W ≥ 250; G ≥ 25 Overhead
W*; G ≥ 7 W ≥ 120; G ≥ 15 Post-mounted
Black on Yellow
or
Black on Orange 		Y*; O* Y ≥ 50; O ≥ 50 2
Y*; O* Y ≥ 75; O ≥ 75 3
White on Red W ≥ 35; R ≥ 7 4
Black on White W ≥ 50 —

Notes:
1 The minimum maintained retroreflectivity levels shown in this table are in units of cd/lx/m2 measured at an observation angle of 0.2° and an entrance angle of -4.0°.
2 For text and fine symbol signs measuring at least 48 inches and for all sizes of bold symbol signs
3 For text and fine symbol signs measuring less than 48 inches
4 Minimum sign contrast ratio ≥ 3:1 (white retroreflectivity ÷ red retroreflectivity)
* This sheeting type shall not be used for this color for this application.

Bold Symbol Signs
  • W1-1, -2 – Turn and Curve
  • W1-3, -4 – Reverse Turn and Curve
  • W1-5 – Winding Road
  • W1-6, -7 – Large Arrow
  • W1-8 – Chevron
  • W1-10 – Intersection in Curve
  • W1-11 – Hairpin Curve
  • W1-15 – 270 Degree Loop
  • W2-1 – Cross Road
  • W2-2, -3 – Side Road
  • W2-4, -5 – T and Y Intersection
  • W2-6 – Circular Intersection
  • W2-7, -8 – Double Side Roads
  • W3-1 – Stop Ahead
  • W3-2 – Yield Ahead
  • W3-3 – Signal Ahead
  • W4-1 – Merge
  • W4-2 – Lane Ends
  • W4-3 – Added Lane
  • W4-5 – Entering Roadway Merge
  • W4-6 – Entering Roadway Added Lane
  • W6-1, -2 – Divided Highway Begins and Ends
  • W6-3 – Two-Way Traffic
  • W10-1, -2, -3, -4, -11, -12 – Grade Crossing Advance Warning
  • W11-2 – Pedestrian Crossing
  • W11-3, -4, -16-22 – Large Animals
  • W11-5 – Farm Equipment
  • W11-6 – Snowmobile Crossing
  • W11-7 – Equestrian Crossing
  • W11-8 – Fire Station
  • W11-10 – Truck Crossing
  • W12-1 – Double Arrow
  • W16-5P, -6P, -7P – Pointing Arrow Plaques
  • W20-7 – Flagger
  • W21-1 – Worker
Fine Symbol Signs (symbol signs not listed as bold symbol signs)
Special Cases
  • W3-1 – Stop Ahead: Red retroreflectivity ≥ 7
  • W3-2 – Yield Ahead: Red retroreflectivity ≥ 7; White retroreflectivity ≥ 35
  • W3-3 – Signal Ahead: Red retroreflectivity ≥ 7; Green retroreflectivity ≥ 7
  • W3-5 – Speed Reduction: White retroreflectivity ≥ 50
  • For non-diamond shaped signs such as W14-3 (No Passing Zone), W4-4P (Cross Traffic Does Not Stop), or W13-1P, -2, -3, -6, -7(Speed Advisory Signs), use largest sign dimension to determine proper minimum retroreflectivity level.

Support:
03 Compliance with the Standard in Paragraph 2 is achieved by having a method in place and using the method to maintain the minimum levels established in Table 2A-3. Provided that an assessment or management method is being used, an agency or official having jurisdiction would be in compliance with the Standard in Paragraph 2 even if there are some individual signs that do not meet the minimum retroreflectivity levels at a particular point in time.

Guidance:
04 Except for those signs specifically identified in Paragraph 6, one or more of the following assessment or management methods should be used to maintain sign retroreflectivity:

  1. Visual Nighttime Inspection—The retroreflectivity of an existing sign is assessed by a trained sign inspector conducting a visual inspection from a moving vehicle during nighttime conditions. Signs that are visually identified by the inspector to have retroreflectivity below the minimum levels should be replaced.
  2. Measured Sign Retroreflectivity—Sign retroreflectivity is measured using a retroreflectometer. Signs with retroreflectivity below the minimum levels should be replaced.
  3. Expected Sign Life—When signs are installed, the installation date is labeled or recorded so that the age of a sign is known. The age of the sign is compared to the expected sign life. The expected sign life is based on the experience of sign retroreflectivity degradation in a geographic area compared to the minimum levels. Signs older than the expected life should be replaced.
  4. Blanket Replacement—All signs in an area/corridor, or of a given type, should be replaced at specified intervals. This eliminates the need to assess retroreflectivity or track the life of individual signs. The replacement interval is based on the expected sign life, compared to the minimum levels, for the shortest-life material used on the affected signs.
  5. Control Signs—Replacement of signs in the field is based on the performance of a sample of control signs. The control signs might be a small sample located in a maintenance yard or a sample of signs in the field. The control signs are monitored to determine the end of retroreflective life for the associated signs. All field signs represented by the control sample should be replaced before the retroreflectivity levels of the control sample reach the minimum levels.
  6. Other Methods—Other methods developed based on engineering studies can be used.

Support:
05 Additional information about these methods is contained in the 2007 Edition of FHWA's "Maintaining Traffic Sign Retroreflectivity" (see Section 1A.11).

Option:
06 Highway agencies may exclude the following signs from the retroreflectivity maintenance guidelines described in this Section:

  1. Parking, Standing, and Stopping signs (R7 and R8 series)
  2. Walking/Hitchhiking/Crossing signs (R9 series, R10-1 through R10-4b)
  3. Acknowledgment signs
  4. All signs with blue or brown backgrounds
  5. Bikeway signs that are intended for exclusive use by bicyclists or pedestrians

Section 2A.09 Shapes

Standard:
01 Particular shapes, as shown in Table 2A-4, shall be used exclusively for specific signs or series of signs, unless otherwise provided in the text discussion in this Manual for a particular sign or class of signs.

Table 2A-4. Use of Sign Shapes
Shape Signs
Octagon Stop*
Equilateral Triangle (1 point down) Yield*
Circle Grade Crossing Advance Warning*
Pennant Shape/ Isosceles Triangle
(longer axis horizontal)		 No Passing*
Pentagon (pointed up) School Advance Warning Sign (squared bottom corners)*
County Route Sign (tapered bottom corners)*
Crossbuck
(two rectangles in an "X" configuration)		 Grade Crossing*
Diamond Warning Series
Rectangle (including square) Regulatory Series
Guide Series**
Warning Series
Trapezoid Recreational and Cultural Interest
Area Series
National Forest Route Sign

* This sign shall be exclusively the shape shown.
** Guide series includes general service, specific service, tourist-oriented directional, general information, recreational and cultural interest area, and emergency management signs.

Section 2A.10 Sign Colors

Standard:
01 The colors to be used on standard signs and their specific use on these signs shall be as provided in the applicable Sections of this Manual. The color coordinates and values shall be as described in 23 CFR, Part 655, Subpart F, Appendix.

Support:
02 As a quick reference, common uses of sign colors are shown in Table 2A-5. Color schemes on specific signs are shown in the illustrations located in each appropriate Chapter.

Table 2A-5. Common Uses of Sign Colors
Type of Sign Legend Background
Black Green Red White Yellow Orange Flourescent Yellow-Green Flourescent Pink Black Blue Brown Green Orange* Red* White Yellow* Purple Fluorescent Yellow-Green Fluorescent Pink
Regulatory Regulatory signs use black for the legend   Regulatory signs use red for the legend Regulatory signs use white for the legend         Regulatory signs use black for the background         Regulatory signs use red for the background Regulatory signs use white for the background        
   Prohibitive     Prohibitive Regulatory signs use red for the legend Prohibitive Regulatory signs use white for the legend                   Prohibitive Regulatory signs use red for the background Prohibitive Regulatory signs use white for the background        
   Permissive   Permissive Regulatory signs use green for the legend                         Permissive Regulatory signs use white for the background        
Warning Warning signs use black for the legend                             Warning signs use yellow for the background      
   Pedestrian Pedestrian warning signs use black for the legend                             Pedestrian Warning signs use yellow for the background   Pedestrian Warning signs use fluorescent yellow-green for the background  
   Bicycle Bicycle warning signs use black for the legend                             Bicycle Warning signs use yellow for the background   Bicycle Warning signs use fluorescent yellow-green for the background  
Guide       Guide signs use white for the legend               Guide signs use green for the background              
   Interstate Route       Interstate Route Guide signs use white for the legend           Interstate Route Guide signs use blue for the background       Interstate Route Guide signs use red for the background          
   State Route Interstate Route Guide signs use black for the legend                           Interstate Route Guide signs use white for the background        
   U.S. Route U.S. Route Guide signs use black for the legend                           U.S. Route Guide signs use white for the background        
   County Route         County Route Guide signs use yellow for the legend         County Route Guide signs use blue for the legend                  
   Forest Route       Forest Route Guide signs use white for the legend             Forest Route Guide signs use brown for the background                
   Street Name       Street Name Guide signs use white for the legend                              
   Destination       Destination Guide signs use white for the legend                              
   Reference Location       Reference Location Guide signs use white for the legend                              
Information       Information Guide signs use white for the legend           Information signs use blue for the background                  
   Evacuation Route Evacuation Route Guide signs use white for the legend     Evacuation Route Information signs use blue for the background  
   Road User Service Road User Service Guide signs use white for the legend     Road User Service Information signs use blue for the background  
   Recreational Recreational Guide signs use white in the legend     Recreational Guide signs use brown for the background Recreational Information signs use green for the background  
Temporary Traffic Control Temporary Traffic Control signs use black for the legend     Temporary Traffic Control signs use orange for the background  
Incident Management Incident Management signs use black for the legend     Incident Management signs uses orange for the background   Incident Management signs use fluorescent pink for the background
School School signs use black for the legend         School signs use flourescent yellow-green for the background
ETC-Account Only ETC-Account Only signs use black for the legend                               ETC-Account Only signs use purple for the legend****    
Changeable Message Signs              
   Regulatory   Regulatory CMS signs use red for the legend*** Regulatory CMS signs use white for the legend     Regulatory CMS signs use black for the background      
   Warning     Warning CMS signs use yellow for the legend     Warning CMS signs use black for the background      
   Temporary Traffic Control   Temporary Traffic Control CMS signs use yellow for the legend Temporary Traffic Control CMS signs use orange for the legend   Temporary Traffic Control CMS signs use black for the background    
   Guide   Guide CMS signs use white for the legend     Guide CMS signs use black for the background Guide CMS signs use green for the background**     Guide CMS signs use flourescent yellow-green for the background
   Motorist Services   Motorist Services Guide signs use white for the legend     Motorist Services CMS signs use black for the background Motorist Services CMS signs use blue for the background**    
   Incident Management   Incident Management CMS signs use yellow for the legend     Incident Management CMS signs uses flourescent pink for the legend Incident Management CMS signs use black for the background    
   School, Pedestrian, Bicycle   School, Pedestrian, and Bicycle CMS signs use yellow for the legend   School, Pedestrian, and Bicycle CMS signs use fluorescent yellow-green for the legend School, Pedestrian, and Bicycle CMS signs use black for the background    

* Fluorescent versions of these background colors may also be used.

** These alternative background colors would be provided by blue or green lighted pixels such that the entire CMS would be lighted, not just the legend.

*** Red is used only for the circle and slash or other red elements of a similar static regulatory sign.

**** The use of the color purple on signs is restricted per the provisions of Paragraph 1 of Section 2F.03.

03 Whenever white is specified in this Manual or in the "Standard Highway Signs and Markings" book (see Section 1A.11) as a color, it is understood to include silver-colored retroreflective coatings or elements that reflect white light.

04 The colors coral and light blue are being reserved for uses that will be determined in the future by the Federal Highway Administration.

05 Information regarding color coding of destinations on guide signs, including community wayfinding signs, is contained in Chapter 2D.

Option:
06 The approved fluorescent version of the standard red, yellow, green, or orange color may be used as an alternative to the corresponding standard color.

Section 2A.11 Dimensions

Support:
01 The "Standard Highway Signs and Markings" book (see Section 1A.11) prescribes design details for up to five different sizes depending on the type of traffic facility, including bikeways. Smaller sizes are designed to be used on bikeways and some other off-road applications. Larger sizes are designed for use on freeways and expressways, and can also be used to enhance road user safety and convenience on other facilities, especially on multi-lane divided highways and on undivided highways having five or more lanes of traffic and/or high speeds. The intermediate sizes are designed to be used on other highway types.

Standard:
02 The sign dimensions prescribed in the sign size tables in the various Parts and Chapters in this Manual and in the "Standard Highway Signs and Markings" book (see Section 1A.11) shall be used unless engineering judgment determines that other sizes are appropriate. Except as provided in Paragraph 3, where engineering judgment determines that sizes smaller than the prescribed dimensions are appropriate for use, the sign dimensions shall not be less than the minimum dimensions specified in this Manual. The sizes shown in the Minimum columns that are smaller than the sizes shown in the Conventional Road columns in the various sign size tables in this Manual shall only be used on low-speed roadways, alleys, and private roads open to public travel where the reduced legend size would be adequate for the regulation or warning or where physical conditions preclude the use of larger sizes.

Option:
03 For alleys with restrictive physical conditions and vehicle usage that limits installation of the minimum size sign (or the Conventional Road size sign if no Minimum size is shown), both the sign height and the sign width may be decreased by up to 6 inches.

Guidance:
04 The sizes shown in the Freeway and Expressway columns in the various sign size tables in this Manual should be used on freeways and expressways, and for other higher-speed applications based upon engineering judgment, to provide larger signs for increased visibility and recognition.

05 The sizes shown in the Oversized columns in the various sign size tables in this Manual size should be used for those special applications where speed, volume, or other factors result in conditions where increased emphasis, improved recognition, or increased legibility is needed, as determined by engineering judgment or study.

06 Increases above the prescribed sizes should be used where greater legibility or emphasis is needed. If signs larger than the prescribed sizes are used, the overall sign dimensions should be increased in 6-inch increments.

Standard:
07 Where engineering judgment determines that sizes that are different than the prescribed dimensions are appropriate for use, standard shapes and colors shall be used and standard proportions shall be retained as much as practical.

Guidance:
08 When supplemental plaques are installed with larger sized signs, a corresponding increase in the size of the plaque and its legend should also be made. The resulting plaque size should be approximately in the same relative proportion to the larger sized sign as the conventional sized plaque is to the conventional sized sign.

Section 2A.12 Symbols

Standard:
01 Symbol designs shall in all cases be unmistakably similar to those shown in this Manual and in the "Standard Highway Signs and Markings" book (see Section 1A.11).

Support:
02 New symbol designs are adopted by the Federal Highway Administration based on research evaluations to determine road user comprehension, sign conspicuity, and sign legibility.

03 Sometimes a change from word messages to symbols requires significant time for public education and transition. Therefore, this Manual sometimes includes the practice of using educational plaques to accompany new symbol signs.

Guidance:
04 New warning or regulatory symbol signs not readily recognizable by the public should be accompanied by an educational plaque.

Option:
05 Educational plaques may be left in place as long as they are in serviceable condition.

06 State and/or local highway agencies may conduct research studies to determine road user comprehension, sign conspicuity, and sign legibility.

Guidance:
07 Although most standard symbols are oriented facing left, mirror images of these symbols should be used where the reverse orientation might better convey to road users a direction of movement.

Standard:
08 A symbol used for a given category of signs (regulatory, warning, or guide) shall not be used for a different category of signs, except as specifically authorized in this Manual.

09 Except as provided in Paragraph 11, a recreational and cultural interest area symbol (see Chapter 2M) shall not be used on streets or highways outside of recreational and cultural interest areas.

10 A recreational and cultural interest area guide sign symbol (see Chapter 2M) shall not be used on any regulatory or warning sign on any street, road, or highway.

Option:
11 A recreational and cultural interest area guide sign symbol (see Section 2M.04) may be used on a highway guide sign outside of a recreational and cultural interest area to supplement a comparable word message for which there is no approved symbol for that message in Chapters 2B through 2I or 2N.

Support:
12 Section 2M.07 contains provisions for the use of recreational and cultural interest area symbols to indicate prohibited activities or items in non-road applications.

Section 2A.13 Word Messages

Standard:
01 Except as provided in Section 2A.06, all word messages shall use standard wording and letters as shown in this Manual and in the "Standard Highway Signs and Markings" book (see Section 1A.11).

Guidance:
02 Word messages should be as brief as possible and the lettering should be large enough to provide the necessary legibility distance. A minimum specific ratio of 1 inch of letter height per 30 feet of legibility distance should be used.

03 Abbreviations (see Section 1A.15) should be kept to a minimum.

04 Word messages should not contain periods, apostrophes, question marks, ampersands, or other punctuation or characters that are not letters, numerals, or hyphens unless necessary to avoid confusion.

05 The solidus (slanted line or forward slash) is intended to be used for fractions only and should not be used to separate words on the same line of legend. Instead, a hyphen should be used for this purpose, such as "TRUCKS - BUSES."

Standard:
06 Fractions shall be displayed with the numerator and denominator diagonally arranged about the solidus (slanted line or forward slash). The overall height of the fraction is measured from the top of the numerator to the bottom of the denominator, each of which is vertically aligned with the upper and lower ends of the solidus. The overall height of the fraction shall be determined by the height of the numerals within the fraction, and shall be 1.5 times the height of an individual numeral within the fraction.

Support:
07 The "Standard Highway Signs and Markings" book (see Section 1A.11) contains details regarding the layouts of fractions on signs.

Guidance:
08 When initials are used to represent an abbreviation for separate words (such as "U S" for a United States route), the initials should be separated by a space of between 1/2 and 3/4 of the letter height of the initials.

09 When an Interstate route is displayed in text form instead of using the route shield, a hyphen should be used for clarity, such as "I-50."

Standard:
10 All sign lettering shall be in upper-case letters as provided in the "Standard Highway Signs and Markings" book (see Section 1A.11), unless otherwise provided in this Manual for a particular sign or type of message.

11 The sign lettering for names of places, streets, and highways shall be composed of a combination of lower-case letters with initial upper-case letters.

Support:
12 Letter height is expressed in terms of the height of an upper-case letter. For mixed-case legends (those composed of an initial upper-case letter followed by lower-case letters), the height of the lower-case letters is derived from the specified height of the initial upper-case letter based on a prescribed ratio. Letter heights for mixed-case legends might be expressed in terms of both the upper- and lower-case letters, or in terms of the initial upper-case letter alone. When the height of a lower-case letter is specified or determined from the prescribed ratio, the reference is to the nominal loop height of the letter. The term loop height refers to the portion of a lower-case letter that excludes any ascending or descending stems or tails of the letter, such as with the letters "d" or "q." The nominal loop height is equal to the actual height of a non-rounded lower-case letter whose form does not include ascending or descending stems or tails, such as the letter "x." The rounded portions of a lower-case letter extend slightly above and below the baselines projected from the top and bottom of such a non-rounded letter so that the appearance of a uniform letter height within a word is achieved. The actual loop height of a rounded lower-case letter is slightly greater than the nominal loop height and this additional height is excluded from the expression of the lower-case letter height.

Standard:
13 When a mixed-case legend is used, the height of the lower-case letters shall be 3/4 of the height of the initial upper-case letter.

14 The unique letter forms for each of the Standard Alphabet series shall not be stretched, compressed, warped, or otherwise manipulated.

Support:
15 Section 2D.04 contains information regarding the acceptable methods of modifying the length of a word for a given letter height and series.

Section 2A.14 Sign Borders

Standard:
01 Unless otherwise provided, each sign illustrated in this Manual shall have a border of the same color as the legend, at or just inside the edge.

02 The corners of all sign borders shall be rounded, except for STOP signs.

Guidance:
03 A dark border on a light background should be set in from the edge, while a light border on a dark background should extend to the edge of the sign. A border for 30-inch signs with a light background should be from 1/2 to 3/4 inch in width, 1/2 inch from the edge. For similar signs with a light border, a width of 1 inch should be used. For other sizes, the border width should be of similar proportions, but should not exceed the stroke-width of the major lettering of the sign. On signs exceeding 72 x 120 inches in size, the border should be 2 inches wide, or on larger signs, 3 inches wide. Except for STOP signs and as otherwise provided in Section 2E.16, the corners of the sign should be rounded to a radius that is concentric with that of the border.

Section 2A.15 Enhanced Conspicuity for Standard Signs

Option:
01 Based upon engineering judgment, where the improvement of the conspicuity of a standard regulatory, warning, or guide sign is desired, any of the following methods may be used, as appropriate, to enhance the sign's conspicuity (see Figure 2A-1):

Figure 2A-1 Examples of Enhanced Conspicuity for Signs

Thumbnail image of Figure 2A-1

  1. Increasing the size of a standard regulatory, warning, or guide sign.
  2. Doubling-up of a standard regulatory, warning, or guide sign by adding a second identical sign on the left-hand side of the roadway.
  3. Adding a solid yellow or fluorescent yellow rectangular "header panel" above a standard regulatory sign, with the width of the panel corresponding to the width of the standard regulatory sign. A legend of "NOTICE," "STATE LAW," or other appropriate text may be added in black letters within the header panel for a period of time determined by engineering judgment.
  4. Adding a NEW plaque (see Section 2C.62) above a new standard regulatory or warning sign, for a period of time determined by engineering judgment, to call attention to the new sign.
  5. Adding one or more red or orange flags (cloth or retroreflective sheeting) above a standard regulatory or warning sign, with the flags oriented so as to be at 45 degrees to the vertical.
  6. Adding a solid yellow, a solid fluorescent yellow, or a diagonally striped black and yellow (or black and fluorescent yellow) strip of retroreflective sheeting at least 3 inches wide around the perimeter of a standard warning sign. This may be accomplished by affixing the standard warning sign on a background that is 6 inches larger than the size of the standard warning sign.
  7. Adding a warning beacon (see Section 4L.03) to a standard regulatory (other than a STOP or a Speed Limit sign), warning, or guide sign.
  8. Adding a speed limit sign beacon (see Section 4L.04) to a standard Speed Limit sign.
  9. Adding a stop beacon (see Section 4L.05) to a STOP sign.
  10. Adding light emitting diode (LED) units within the symbol or legend of a sign or border of a standard regulatory, warning, or guide sign, as provided in Section 2A.07.
  11. Adding a strip of retroreflective material to the sign support in compliance with the provisions of Section 2A.21.
  12. Using other methods that are specifically allowed for certain signs as described elsewhere in this Manual.

Support:
02 Sign conspicuity improvements can also be achieved by removing non-essential and illegal signs from the right-of-way (see Section 1A.08), and by relocating signs to provide better spacing.

Standard:
03 The NEW plaque (see Section 2C.62) shall not be used alone.

04 Strobe lights shall not be used to enhance the conspicuity of highway signs.

Section 2A.16 Standardization of Location

Support:
01 Standardization of position cannot always be attained in practice. Examples of heights and lateral locations of signs for typical installations are illustrated in Figure 2A-2, and examples of locations for some typical signs at intersections are illustrated in Figures 2A-3 and 2A-4.

Figure 2A-2 Examples of Heights and Lateral Locations of Sign Installations

Thumbnail image of Figure 2A-2

Figure 2A-3 Examples of Locations for Some Typical Signs at Intersections

Thumbnail image of Figure 2A-3

02 Examples of advance signing on an intersection approach are illustrated in Figure 2A-4. Chapters 2B, 2C, and 2D contain provisions regarding the application of regulatory, warning, and guide signs, respectively.

Figure 2A-4 Relative Locations of Regulatory, Warning, and Guide Signs on an Intersection Approach

Thumbnail image of Figure 2A-4

Standard:
03 Signs requiring separate decisions by the road user shall be spaced sufficiently far apart for the appropriate decisions to be made. One of the factors considered when determining the appropriate spacing shall be the posted or 85th-percentile speed.

Guidance:
04 Signs should be located on the right-hand side of the roadway where they are easily recognized and understood by road users. Signs in other locations should be considered only as supplementary to signs in the normal locations, except as otherwise provided in this Manual.

05 Signs should be individually installed on separate posts or mountings except where:

  1. One sign supplements another;
  2. Route or directional signs are grouped to clarify information to motorists;
  3. Regulatory signs that do not conflict with each other are grouped, such as turn prohibition signs posted with one way signs or a parking regulation sign posted with a speed limit sign; or
  4. Street name signs are posted with a stop or yield sign.

06 Signs should be located so that they:

  1. Are outside the clear zone unless placed on a breakaway or yielding support (see Section 2A.19),
  2. Optimize nighttime visibility,
  3. Minimize the effects of mud splatter and debris,
  4. Do not obscure each other,
  5. Do not obscure the sight distance to approaching vehicles on the major street for drivers who are stopped on minor-street approaches, and
  6. Are not hidden from view.

Support:
07 The clear zone is the total roadside border area, starting at the edge of the traveled way, available for use by errant vehicles. The width of the clear zone is dependent upon traffic volumes, speeds, and roadside geometry. Additional information can be found in AASHTO's "Roadside Design Guide" (see Section 1A.11).

Guidance:
08 With the increase in traffic volumes and the desire to provide road users regulatory, warning, and guidance information, an order of priority for sign installation should be established.

Support:
09 An order of priority is especially critical where space is limited for sign installation and there is a demand for several different types of signs. Overloading road users with too much information is not desirable.

Guidance:
10 Because regulatory and warning information is more critical to the road user than guidance information, regulatory and warning signing whose location is critical should be displayed rather than guide signing in cases where conflicts occur. Community wayfinding and acknowledgment guide signs should have a lower priority as to placement than other guide signs. Information of a less critical nature should be moved to less critical locations or omitted.

Option:
11 Under some circumstances, such as on curves to the right, signs may be placed on median islands or on the left-hand side of the road. A supplementary sign located on the left-hand side of the roadway may be used on a multi-lane road where traffic in a lane to the right might obstruct the view to the right.

Guidance:
12 In urban areas where crosswalks exist, signs should not be placed within 4 feet in advance of the crosswalk (see Drawing D in Figure 2A-3).

Section 2A.17 Overhead Sign Installations

Guidance:
01 Overhead signs should be used on freeways and expressways, at locations where some degree of lane-use control is desirable, and at locations where space is not available at the roadside.

Support:
02 The operational requirements of the present highway system are such that overhead signs have value at many locations. The factors to be considered for the installation of overhead sign displays are not definable in specific numerical terms.

Option:
03 The following conditions (not in priority order) may be considered in an engineering study to determine if overhead signs would be beneficial:

  1. Traffic volume at or near capacity,
  2. Complex interchange design,
  3. Three or more lanes in each direction,
  4. Restricted sight distance,
  5. Closely-spaced interchanges,
  6. Multi-lane exits,
  7. Large percentage of trucks,
  8. Street lighting background,
  9. High-speed traffic,
  10. Consistency of sign message location through a series of interchanges,
  11. Insufficient space for post-mounted signs,
  12. Junction of two freeways, and
  13. Left exit ramps.

04 Over-crossing structures may be used to support overhead signs.

Support:
05 Under some circumstances, the use of over-crossing structures as sign supports might be the only practical solution that will provide adequate viewing distance. The use of such structures as sign supports might eliminate the need for the foundations and sign supports along the roadside.

Section 2A.18 Mounting Height

Standard:
01 The provisions of this Section shall apply unless specifically stated otherwise for a particular sign or object marker elsewhere in this Manual.

Support:
02 The mounting height requirements for object markers are provided in Chapter 2C.

03 In addition to the provisions of this Section, information affecting the minimum mounting height of signs as a function of crash performance can be found in AASHTO's "Roadside Design Guide" (see Section 1A.11).

Standard:
04 The minimum height, measured vertically from the bottom of the sign to the elevation of the near edge of the pavement, of signs installed at the side of the road in rural areas shall be 5 feet (see Figure 2A-2).

05 The minimum height, measured vertically from the bottom of the sign to the top of the curb, or in the absence of curb, measured vertically from the bottom of the sign to the elevation of the near edge of the traveled way, of signs installed at the side of the road in business, commercial, or residential areas where parking or pedestrian movements are likely to occur, or where the view of the sign might be obstructed, shall be 7 feet (see Figure 2A-2).

Option:
06 The height to the bottom of a secondary sign mounted below another sign may be 1 foot less than the height specified in Paragraphs 4 and 5.

Standard:
07 The minimum height, measured vertically from the bottom of the sign to the sidewalk, of signs installed above sidewalks shall be 7 feet.

08 If the bottom of a secondary sign that is mounted below another sign is mounted lower than 7 feet above a pedestrian sidewalk or pathway (see Section 6D.02), the secondary sign shall not project more than 4 inches into the pedestrian facility.

Option:
09 Signs that are placed 30 feet or more from the edge of the traveled way may be installed with a minimum height of 5 feet, measured vertically from the bottom of the sign to the elevation of the near edge of the pavement.

Standard:
10 Directional signs on freeways and expressways shall be installed with a minimum height of 7 feet, measured vertically from the bottom of the sign to the elevation of the near edge of the pavement. All route signs, warning signs, and regulatory signs on freeways and expressways shall be installed with a minimum height of 7 feet, measured vertically from the bottom of the sign to the elevation of the near edge of the pavement. If a secondary sign is mounted below another sign on a freeway or expressway, the major sign shall be installed with a minimum height of 8 feet and the secondary sign shall be installed with a minimum height of 5 feet, measured vertically from the bottom of the sign to the elevation of the near edge of the pavement.

11 Where large signs having an area exceeding 50 square feet are installed on multiple breakaway posts, the clearance from the ground to the bottom of the sign shall be at least 7 feet.

Option:
12 A route sign assembly consisting of a route sign and auxiliary signs (see Section 2D.31) may be treated as a single sign for the purposes of this Section.

13 The mounting height may be adjusted when supports are located near the edge of the right-of-way on a steep backslope in order to avoid the sometimes less desirable alternative of placing the sign closer to the roadway.

Standard:
14 Overhead signs shall provide a vertical clearance of not less than 17 feet to the sign, light fixture, or sign bridge over the entire width of the pavement and shoulders except where the structure on which the overhead signs are to be mounted or other structures along the roadway near the sign structure have a lesser vertical clearance.

Option:
15 If the vertical clearance of other structures along the roadway near the sign structure is less than 16 feet, the vertical clearance to an overhead sign structure or support may be as low as 1 foot higher than the vertical clearance of the other structures in order to improve the visibility of the overhead signs.

16 In special cases it may be necessary to reduce the clearance to overhead signs because of substandard dimensions in tunnels and other major structures such as double-deck bridges.

Support:
17 Figure 2A-2 illustrates some examples of the mounting height requirements contained in this Section.

Section 2A.19 Lateral Offset

Standard:
01 For overhead sign supports, the minimum lateral offset from the edge of the shoulder (or if no shoulder exists, from the edge of the pavement) to the near edge of overhead sign supports (cantilever or sign bridges) shall be 6 feet. Overhead sign supports shall have a barrier or crash cushion to shield them if they are within the clear zone.

02 Post-mounted sign and object marker supports shall be crashworthy (breakaway, yielding, or shielded with a longitudinal barrier or crash cushion) if within the clear zone.

Guidance:
03 For post-mounted signs, the minimum lateral offset should be 12 feet from the edge of the traveled way. If a shoulder wider than 6 feet exists, the minimum lateral offset for post-mounted signs should be 6 feet from the edge of the shoulder.

Support:
04 The minimum lateral offset requirements for object markers are provided in Chapter 2C.

05 The minimum lateral offset is intended to keep trucks and cars that use the shoulders from striking the signs or supports.

Guidance:
06 All supports should be located as far as practical from the edge of the shoulder. Advantage should be taken to place signs behind existing roadside barriers, on over-crossing structures, or other locations that minimize the exposure of the traffic to sign supports.

Option:
07 Where permitted, signs may be placed on existing supports used for other purposes, such as highway traffic signal supports, highway lighting supports, and utility poles.

Standard:
08 If signs are placed on existing supports, they shall meet other placement criteria contained in this Manual.

Option:
09 Lesser lateral offsets may be used on connecting roadways or ramps at interchanges, but not less than 6 feet from the edge of the traveled way.

10 On conventional roads in areas where it is impractical to locate a sign with the lateral offset prescribed by this Section, a lateral offset of at least 2 feet may be used.

11 A lateral offset of at least 1 foot from the face of the curb may be used in business, commercial or residential areas where sidewalk width is limited or where existing poles are close to the curb.

Guidance:
12 Overhead sign supports and post-mounted sign and object marker supports should not intrude into the usable width of a sidewalk or other pedestrian facility.

Support:
13 Figures 2A-2 and 2A-3 illustrate some examples of the lateral offset requirements contained in this Section.

Section 2A.20 Orientation

Guidance:
01 Unless otherwise provided in this Manual, signs should be vertically mounted at right angles to the direction of, and facing, the traffic that they are intended to serve.

02 Where mirror reflection from the sign face is encountered to such a degree as to reduce legibility, the sign should be turned slightly away from the road. Signs that are placed 30 feet or more from the pavement edge should be turned toward the road. On curved alignments, the angle of placement should be determined by the direction of approaching traffic rather than by the roadway edge at the point where the sign is located.

Option:
03 On grades, sign faces may be tilted forward or back from the vertical position to improve the viewing angle.

Section 2A.21 Posts and Mountings

Standard:
01 Sign posts, foundations, and mountings shall be so constructed as to hold signs in a proper and permanent position, and to resist swaying in the wind or displacement by vandalism.

Support:
02 The latest edition of AASHTO's "Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals" contains additional information regarding posts and mounting (see Page i for AASHTO's address).

Option:
03 Where engineering judgment indicates a need to draw attention to the sign during nighttime conditions, a strip of retroreflective material may be used on regulatory and warning sign supports.

Standard:
04 If a strip of retroreflective material is used on the sign support, it shall be at least 2 inches in width, it shall be placed for the full length of the support from the sign to within 2 feet above the edge of the roadway, and its color shall match the background color of the sign, except that the color of the strip for the YIELD and DO NOT ENTER signs shall be red.

Section 2A.22 Maintenance

Guidance:
01 Maintenance activities should consider proper position, cleanliness, legibility, and daytime and nighttime visibility (see Section 2A.09). Damaged or deteriorated signs, gates, or object markers should be replaced.

02 To assure adequate maintenance, a schedule for inspecting (both day and night), cleaning, and replacing signs, gates, and object markers should be established. Employees of highway, law enforcement, and other public agencies whose duties require that they travel on the roadways should be encouraged to report any damaged, deteriorated, or obscured signs, gates, or object markers at the first opportunity.

03 Steps should be taken to see that weeds, trees, shrubbery, and construction, maintenance, and utility materials and equipment do not obscure the face of any sign or object marker.

04 A regular schedule of replacement of lighting elements for illuminated signs should be maintained.

Section 2A.23 Median Opening Treatments for Divided Highways with Wide Medians

Guidance:
01 Where divided highways are separated by median widths at the median opening itself of 30 feet or more, median openings should be signed as two separate intersections.

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