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Minimum Retroreflectivity Levels for Overhead Guide Signs and Street-Name Signs

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CHAPTER 3. CURRENT PRACTICES

This chapter describes the activities and findings associated with a review of current State and local agency practices related to overhead guide signs and street-name signs. This task was conducted to establish a fundamental understanding of the design and application practices for those types of signs.

ACTIVITIES

The activities associated with this effort included a review of State and national versions of the MUTCD and a survey of State and local agency personnel. The results of the MUTCD reviews and the survey of transportation agencies are divided by subject into overhead signs and street-name signs.

Review of National and State MUTCDs

The MUTCD establishes the guiding principles for the use of traffic control devices, including overhead and street-name signs. When this review was conducted, the 1988 MUTCD was the current edition of the national manual. However, FHWA has since developed and published a new edition. In the first effort of this task, the researchers reviewed the applicable portions of the 1988 MUTCD and then proposed a Millennium Manual (it had not been published when this review occurred) to establish the basic principles for the design and placement of overhead signs and street-name signs.

The MUTCD issued by the Federal Government is referred to as the national MUTCD and it is intended to promote national uniformity of traffic control devices. However, because the Federal Government does not build and maintain roadways (with a few exceptions, such as forest roads), the Federal Government is not responsible for placing and maintaining traffic control devices. Federal and State laws require each State to adopt a traffic control device manual that meets or exceeds the requirements of the national manual. These State manuals can take one of three different forms: the national MUTCD, the national MUTCD with a State supplement, or a State manual. Almost half of the States have adopted the national MUTCD as a complete document without any changes. But more than half of the States have made changes to the national MUTCD through a State supplement or a State version of the MUTCD. Despite the existence of a national MUTCD, the fact that there are different versions of the MUTCD in the various States can lead to important differences from one part of the United States to another. Therefore, as part of this activity, the researchers also reviewed several State MUTCDs for information regarding the design of overhead and street-name signs. The State MUTCDs, or their equivalents, that were reviewed included:

• Caltrans Traffic Manual.⁽⁵²⁾
• Maryland Supplement to the Manual on Uniform Traffic Control Devices.⁽⁵³⁾
• Minnesota Manual on Uniform Traffic Control Devices.⁽⁵⁴⁾
• PennDOT Handbook of Approved Signs.⁽⁵⁵⁾
• Texas Manual on Uniform Traffic Control Devices.⁽⁵⁶⁾

Survey of Practitioners

The MUTCD establishes minimum standards and guidelines, which are often exceeded in common practices. Furthermore, other than the courtroom, there Is no enforcement mechanism for the MUTCD. Therefore, it is not uncommon for MUTCD principles to be violated (knowingly or unknowingly) in actual practice. In order to assess the differences between the MUTCD principles and actual practices, researchers conducted an e-mail survey of practitioners at State and local transportation agencies.

The survey was distributed to five State and five local agencies. Table 9 lists the nine agencies that responded. Figure 1 presents the questions submitted to the practitioners. The complete survey as sent to the practitioners is included in appendix A. Appendix A also contains the complete responses as received from the agencies for overhead signs and street-name signs. The results from the surveys are summarized and discussed in the sections addressing overhead signs and street-name signs.

Table 9. List of Transportation Agencies That Responded

OVERHEAD SIGNS

Overhead signs are any signs that are mounted in a manner that allows vehicles to drive under the signs. These signs are typically placed on sign bridges or cantilever sign supports. Overhead signs can also be placed on traffic signal mast arms. The most common type of overhead sign is the freeway guide sign. For this research study, the researchers were concerned about overhead guide signs, overhead street-name signs, and post-mounted street-name signs.

Other types of signs may also be placed overhead. The researchers have observed regulatory, warning, construction, and services signs mounted overhead. Commonly used overhead regulatory signs include signal-related signs (LEFT TURN SIGNAL, LEFT TURN YIELD ON [green ball], NO LEFT TURN, etc.), lane-use control signs, hazardous cargo signs, and others. Examples of warning signs that may be mounted overhead include a LANE ENDS sign, an advisory exit speed sign, an EXIT ONLY panel, and others. The Initial minimum levels published by FHWA did not address yellow, orange, or red signs mounted in the overhead position.

There are a number of factors that have a significant effect on the nighttime visibility of overhead signs. The most significant of these Is the lower level of illumination reaching signs in the overhead position. Other factors include, but are not limited to, variations in signing materials (including button copy), variations in legend size and design, and variations in mounting height.

Previous Efforts on MR Levels

MR levels for overhead signs were Included in the original FHWA recommendations for white background signs and green background signs only. There were no levels proposed for yellow or red background overhead signs. When the MR levels were revised, the levels for overhead signs were eliminated. The original MR recommendations for white-and-green overhead signs are shown in tables 6 and 7. These tables also include the revised levels where the minimum levels for the overhead signs were eliminated.

Review of MUTCD Principles

As indicated previously, the overhead sign portion of this project is focusing upon overhead guide signs. In conducting the review of MUTCD principles for overhead guide signs, the researchers reviewed the expressway and freeway chapters of the MUTCD. MUTCDs, or the equivalent manuals, were evaluated from the following States: California, Maryland, Minnesota, and Texas. The following provides some of the key findings from the review as they relate to the visibility or retroreflectivity aspects of overhead signs:

• Overhead Sign Height
  • 1988 National MUTCD: Overhead signs should be mounted to provide a vertical clearance of at least 17 ft over the entire length of the roadway (including the shoulders). This height may change where other structures use lower clearances and under special circumstances (tunnels, double-decker bridges, etc.).
  • Other States: Same as the national MUTCD except as noted below:
  • Overhead signs are to have a minimum vertical clearance of 18 ft. Overhead signs shall be placed 30 ft from any light standards.
  • Overhead signs are to be mounted with a minimum vertical clearance of 17 ft-6 inches over the entire length of the roadway. The height of the sign should not initially exceed 23 ft. When the height is reduced to less than 16 ft-6 inches, consider raising the sign.
• Mounting Issues (number of sign panels)
  • 1988 National MUTCD: No more than three overhead signs at one location.
  • Other State MUTCDs: Same as the national MUTCD.
• Amount of Legend
  • 1988 National MUTCD: Legend is fixed at a maximum of two destination names or street names. Directional copy should not exceed three lines. When two or more signs are used together, it is desirable to limit destinations or names to one per sign.
  • Other State MUTCDs: Same as the national MUTCD.
• Legend Size
  • 1988 National MUTCD: For both rural and urban areas, lettering should be a minimum of 8 inches high. Uppercase letters are used for all word legends. Lowercase letters with an initial uppercase letter are used for all places, streets, and highways. The uppercase lettering shall be 1.33 times the loop height of the lowercase lettering. Table 10 contains letter heights based on the type of overhead sign. These range from 10 to 18 inches on overhead signs. For example, numerals (15 inches) are larger than words (10 inches) and single letters are also 15 inches.
  • Other State MUTCDs: Same as the national MUTCD.
• Type of Alphabet
  • 1988 National MUTCD: Not specified for expressways; however, for freeways, the Initial alphabet will be Series E (Modified).
  • Other State MUTCDs: Same as the national MUTCD.

Survey of Agency Practices

As mentioned previously, the researchers also conducted a survey of five State and five local agencies to identify the actual practices related to overhead signs. Table 9 lists the agencies that responded to the survey. Figure 1 presents the questions that were part of the survey. The complete responses to the overhead sign questions from each agency are contained in appendix A. Tables 10 and 11 provide a capsule summary of the survey responses from each agency.

STREET-NAME SIGNS

There are several different types of street-name signs. The most common is the post-mounted horizontal rectangular sign. This type of street-name sign is often mounted above another type of sign, such as a STOP sign. Another common type of street-name sign is mounted on traffic signal mast arms or span wire. Street-name signs are also used in advance of intersections, alone or in combination with other types of signs (such as a crossroad warning sign, W2-1).

There are great variations in the type, design, and placement of street-name signs. The most common is the white on green with 6-inch letters. There are also great variations in the type of legend used on street-name signs. Some agencies simply provide the street name. Others include the street classification (Rd, St, Blvd, Ave, etc.) and/or a block number. The legend may be In capitals or in uppercase/lowercase letters. There are many agencies that use colors other than white on green.

Table 10. State Agency Responses to Overhead Sign Questions

Table 11. Local Agency Responses to Overhead Sign Questions

There are a number of factors that have a significant effect on the nighttime visibility of street-name signs. These signs are often mounted on only one corner of an intersection, presenting a disadvantaged (left side) position for two of the four approaches. They may also be as high as 10 ft or more If they are mounted above a STOP or YIELD sign. These factors reduce the Illumination reaching the signs, thereby reducing the luminance of the signs. Because of the length of many street names, a narrow stroke-width alphabet (Series B or C) is often used, reducing the legibility of the signs.

Previous Efforts on MR Levels

MR levels for street-name signs were not specifically excluded from the original FHWA recommendations. However, a review of the CARTS model indicates that street-name signs were not in the sign library and were therefore probably not addressed in the development of MR levels. Street-name signs were specifically excluded when the MR levels were revised.

Review of MUTCD Principles

In conducting the review of MUTCD principles for street-name signs, the researchers reviewed the conventional guide sign chapter of the MUTCD. MUTCDs, or the equivalent manuals, were evaluated from the following States: California, Maryland, Minnesota, Pennsylvania, and Texas. The following provides some of the key findings from the review as they relate to the visibility or retroreflectivity aspects of street-name signs:

• Sign Color
• • 1988 National MUTCD: Legend and background shall be of contrasting colors, specifically a white legend and border on a green background. The sign should also be reflectorized or illuminated. When paired with an advance warning sign, colors will be black on a yellow background.
  • Other State MUTCDs: Same as the national MUTCD except as noted below:
  • Post-mounted signs are to have color combinations visible to 150 ft during the day and under normal weather conditions.
  • Legend and background shall be of contrasting colors.
  • White legend on a green background, black legend on a white background, or other contrasting combination.
• Sign Legend (street name, block number, direction, symbol)
• • 1988 National MUTCD: Legend consists of street name and street designation (avenue, street, etc.). The legend may also have cardinal directions and a symbol identifying the governmental jurisdiction. The sign may use conventional abbreviations; however, the street name may not be abbreviated.
  • Other States: Same as the national MUTCD.
• Legend Size
  • 1988 National MUTCD: The legend shall be a minimum of 4-inch lettering. Supplemental lettering shall be at least 2 inches in height. Any symbols will be to the left of the street name and will be less than or equal to the height of the sign.
  • 1988 National MUTCD Revision 5: The 1988 MUTCD was revised to require the legend on street-name signs to be at least 6 inches high. If uppercase and lowercase letters are used, then the uppercase letters should be 6 inches, with 4.5-inch lowercase letters. Abbreviated lettering to indicate the type of street or section of the city (e.g., Ave., N.W., etc.) may be In smaller lettering (at least 3 inches high). However, for local roads with speed limits 25 mph or less, the lettering may be a minimum of 4 inches, with 2-inch letters for street abbreviations or city sections.
  • Other State MUTCDs: Same as the national MUTCD except as noted below:
  • The lettering for urban streets and less important rural roads shall be 4 inches high. When using lowercase letters, the uppercase letter height will be 1.33 times the loop height of the lowercase letters. Supplemental lettering shall be at least 2 inches high. Any symbols will be to the left of the street name and will be less than or equal to the height of the sign.
  • Open capital letters shall be no greater than 4 inches high. Capital letters are to be 4 inches high when used with 3-inch lowercase lettering. The street designation shall be no greater than 2 inches high. Mast-arm-mounted signs are to use a minimum height of 6 inches for uppercase letters and 4.5 inches for lowercase letters.
  • In rural districts, the letter height is 6 inches or more on the principal legend. On urban streets and less important rural roads, the letter height is 4 inches or greater.
  • Use lettering at least 4 inches high. Supplementary lettering uses a 3-inch height.
• Legend Alphabet
• • 1988 National MUTCD: Sign lettering shall be In uppercase letters. The Series B alphabet shall be restricted to limited breadth and width signs (street-name signs).
  • Other State MUTCDs: Same as the national MUTCD.
• Sign Placement
• • 1988 National MUTCD: In business districts and on principal arterial streets, at a minimum, signs shall be placed on diagonally opposite corners such that they are on the far right-hand side of the major traffic flow. In residential areas, there shall be a minimum of one street-name sign at each intersection. There shall also be signs naming both streets at each location. The sign face should be parallel to the street it names.
  • Other State MUTCDs: Same as the national MUTCD except as noted below:
  • Street-name signs at all street intersections in urban areas.
  • At signalized intersections along State highways with mast arms or span wires, street-name signs shall be Installed on the mast arm or span wire for all approaches. At all other signalized intersections, street-name signs should be Installed. All intersections without overhead signs shall have at least one street-type D-3 name sign facing each major approach. Also, there shall be one sign facing each major approach and nonmajor approaches that are not the only exits from private streets, cul-de-sacs, and residential developments. These other approaches should have a street-name sign facing them.
  • Street-name signs are required at all signalized intersections and must be visible from all directions. Two street-name signs, visible from each approach, are required in retail business districts. Signs may be post- or mast-arm-mounted.
  • Street-name signs shall be placed at all street intersections regardless of other route markings already present. In business districts, signs are to be placed on diagonally opposite corners so that the sign will be on the far right-hand side of the major traffic. In residential districts, there will be a single sign for each intersection. Signs may also be placed in a vertical position on a wooden post.
• Sign Height
• • 1988 National MUTCD: Minimum of 5 ft from the bottom of the sign to the near edge of the pavement. Minimum of 7 ft when pedestrians and vehicles may cause a sight obstruction.
  • Other State MUTCDs: Same as the national MUTCD except as noted below:
  • Minimum height of 7 ft over the top of the curb. Two street-name signs on the same pole are to be mounted in the cross position, one over the other. On wooden post signs, the legend is to be at least 5 ft above the road surface.

Survey of Agency Practices

As mentioned, the researchers also conducted a survey of State and local agencies to identify the actual practices related to street-name signs. Table 9 lists the agencies that responded to the survey. Figure 1 presents the questions that were part of the survey. The complete responses to the overhead sign questions from each agency are contained in appendix A. Tables 12 and 13 provide a capsule summary of the survey responses from each agency.

SUMMARY

Based on the activities associated with the review of current practices, the researchers developed the following findings and scenarios related to the overhead signs and street-name signs that were later used in the development of the MR levels.

Findings

The review of MUTCD principles and the survey of agency practices led to the following findings related to the current use of overhead signs and street-name signs:

• Overhead Signs
  • The minimum clearance to the bottom of the overhead signs varies by agency; however, it is typically 17 to 21 ft.
  • There should be no more than three sign panels at a single overhead sign location.
  • There should be no more than two destinations or three lines of legend on a single sign panel.
  • The minimum legend size for destinations is 16-inch uppercase and 12-inch lowercase Series E (Modified) alphabet. The minimum legend for cardinal directions, distances, and other information ranges from 10 to 18 inches.
  • High-intensity (type III) or microprismatic (type IV or Visual Impact Performance (VIP)) sheeting is typically used in new overhead signs. While button-copy legend was once the most common type of legend for overhead signs, it is not being used on new signs to any significant extent. However, there are still many button-copy signs in the field.
  • The use of sign lighting with overhead signs is decreasing.
• Mast-Arm Street-Name Signs
• • Both State and local agencies use mast-arm-mounted street-name signs at major signalized intersections.
  • The height of these signs ranges from 16 to 19 ft.
  • The legend size ranges from 6 to 10 inches.
  • Several different alphabets are used for mast-arm street-name signs, ranging from Series B to E (Modified).
  • These signs are white on green.
  • High-intensity (type III) or microprismatic (type IV or VIP) sheeting is typically used in mast-arm street-name signs.
• Post-Mounted Street-Name Signs
  • Street-name signs are located on both the right and left sides of the road. On major roads, street-name signs are more likely to be found on the right side of the major road at opposing corners.
  • Post-mounted street-name signs are often 9 to 10 ft high because of their being mounted above STOP and YIELD signs.
  • While a recent revision of the 1988 MUTCD increased the minimum size of the legend on street-name signs to 6 inches, there are many existing signs with 4-inch legends and agencies that still use 4-inch legends. Some of the 6-inch legends use the Series E (Modified) alphabet, with a 4-inch loop height for the lowercase letters.
  • Street-name signs commonly use Series C and D alphabets. Some local agencies use Series E (Modified) uppercase/lowercase letters. Local agencies also use the Series B alphabet in some cases. The choice of an alphabet to be used is often based on the size of the street name. A long street name will use a narrower stroke-width alphabet.
  • White on green is the most common color. Other colors are allowed; however, the use of other colors does not appear to be widespread.
  • Retroreflective sheeting used on street-name signs ranges from type I to microprismatic.

 Table 13. Local Agency Responses to Street-Name Sign Questions

Scenarios

Based on these findings, the researchers developed the following scenarios that represent best-case, typical, and worst-case situations for nighttime visual performance of overhead guide signs and street-name signs:

• Overhead Signs
  • Best Case: 17 ft high, 16-inch uppercase and 12-inch lowercase Series E (Modified) legend, single sign panel with minimal copy, appropriate sign lighting.
  • Typical Case: 18 ft high, 16-inch uppercase and 12-inch lowercase Series E (Modified) legend, two sign panels with one or two destinations per sign panel, no sign lighting, and panel is located directly ahead or to the right of the vehicle.
  • Worst Case: 21 ft high, 16-inch uppercase and 12-inch lowercase Series E (Modified) legend, three sign panels with complicated copy, no sign lighting, and sign panel of interest is located to the left of the vehicle.
• Mast-Arm Street-Name Signs
  • Best Case: Right side, 16 ft high, 10-inch Series E (Modified) legend, white on green.
  • Typical Case: Right edge of lane, 17 ft high, 8-inch Series E (Modified) legend, white on green.
  • Worst Case: Head on, 19 ft high, 6-inch Series C legend, white on green.
• Post-Mounted Street-Name Sign
  • Best Case: Right side, 7 ft high, 6-inch Series E (Modified) legend, white on green.
  • Typical Case: Right side, 9 ft high, 6-inch Series C or D legend, white on green.
  • Worst Case: Left side, 10 ft high, 4-inch Series B legend,white on brown.

   

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