APPENDIX A. SURVEY OF CURRENT PRACTICES

Figure 23 presents the complete e-mail message sent to the State and local transportation agencies. The survey was sent to five State agencies, three city agencies, and two county agencies. All but one responded. In the detailed responses below, "State" refers to a comment from a State agency, "city" refers to a city response, and "county" refers to a county response.

OVERHEAD SIGN SURVEY RESPONSES

This section provides the detailed responses submitted by respondents to each question in the overhead sign portion of the e-mail survey.

General Comments

1. State: None.
2. State: None.
3. State: None.
4. State: None.
5. State: None.
6. City: With the exception of signs on signal mast arms, we rarely install overhead signs. Answers to this category of questions are based on street-name signs on signal poles.
7. County: None.
8. County: None.
9. City: We do not use "overhead signs" in the usual sense. The only overhead signs installed in the city would be those installed on our overhead traffic signal mast-arm poles. These would include street-name signs, ONE WAY signs, and lane-use control signs. We generally use standard layouts for these and historically have used engineering-grade sheeting (except as noted below).

1. What size is the legend (typical letter height)?
   1. State: Typical letter height for the legend is 16-inch uppercase and 12-inch lowercase.
   2. State: We use the table in section 2F of the MUTCD.
   3. State: 16-inch uppercase and 12-inch lowercase. The legend on freeway-to-freeway guide signs and freeway exit direction signs is 20-inch uppercase and 15-inch lowercase.
   4. State: Standard legend (letter height) sizes specified in the Federal MUTCD.
   5. State: 16-inch uppercase and 12-inch lowercase.
   6. City: 10 inches.
   7. County: 8-inch uppercase and 6-inch lowercase.
   8. County: 6 inches.
   9. City: See general comment.
2. 2. What alphabet is used for the legend (Series E (Modified), other)?
   1. State: Alphabet is Federal alphabet Series E (Modified).
   2. State: Series E (Modified) since this is the only series with uppercase/lowercase lettering. What happen to the 3M research for the new letter series (Clearview or something like that)?
   3. State: Series E (Modified).
   4. State: Series E (Modified).
   5. State: Series E (Modified).
   6. City: Series B and C.
   7. County: Series C.
   8. County: Series E (Modified).
   9. City: See general comment.
3. What sheeting material(s) do you use for overhead signs (background and legend)?
   1. State: Materials for legend and background are high-intensity, type III or IV.
   2. State: Type III.
   3. State: Type III for both.
   4. State: On March 1, 1999, our agency adopted the Wide-Angle Prismatic Retroreflective Sheeting for Visual Impact Performance (VIP) manufactured by 3M (sole-source specification) for ALL permanent regulatory, warning, guide, and supplemental guide signs, except for Adopt-A-Highway signs, snowplow markers, and the blue background of logo signs (Federal Specific Service signs). These three exceptions use type III (high-intensity reflective sheeting). Note: VIP sheeting requires that any overhead signs made of extruded aluminum need to be covered with 0.063-inch sheet aluminum with Direct Applied sheeting for legends and backgrounds. Note: Since brown is not available in VIP sheeting, we specify white VIP sheeting for the background material and brown electronic cuttable (EC) film manufactured by 3M (with the legend cut out of the EC film. Also: On route markers attached to overhead guide signs, the sign legend materials for colors other than black may be screen-processed painted legend. Black legend may be either screen-processed painted legend or pigmented plastic film legend.
   5. State: Type III for both.
   6. City: Green EC film on white high-intensity sheeting.
   7. County: High-intensity.
   8. County: VIP for both.
   9. City: See general comment.
4. Do you use a higher grade of sheeting for overhead signs compared to ground-mounted signs?
   1. State: Same material is used on all guide signs, both overhead and ground-mounted.
   2. State: No.
   3. State: No, however it is our policy to light all overhead signs.
   4. State: See response to question 3.
   5. State: No.
   6. City: No.
   7. County: We are experimenting with diamond-grade and VIP sheeting.
   8. County: Yes, we use high-intensity on red/yellow background ground mount, and engineering grade for white/green/blue ground mount.
   9. City: See general comment.
5. 5. What is the typical height to the bottom of an overhead sign?
   1. State: Typical height to bottom of sign is 18 ft.
   2. State: Our minimum height is 17 ft-6 inches.
   3. State: 20 ft-9 inches from the high-point elevation of the traveled roadway
   4. State: 17 ft-4 inches to the bottom of the low steel of the sign truss or to the bottom of the tallest sign panel (on monotube unlit sign structures).
   5. State: 17 ft.
   6. City: 17 ft-6 inches.
   7. County: Minimum 16 ft, preferred 19 ft.
   8. County: 16 ft-6 inches to 17 ft-0 inches.
   9. ity: See general comment.
6. Do you have any agency guidelines for the design of overhead signs that are different from that contained in your State's MUTCD? (If so, please send us a copy at your convenience.)
   1. State: No, we conform to the Federal MUTCD.
   2. State: No
   3. State: No other than as noted in question 1 above. The only other related design guideline is the application of message dividers.
   4. State: We developed (in conjunction with a private vendor) and beta tested the SignCAD guide sign design program. The SignCAD guide sign design program is Windows^®-based and was designed using the parameters from an old (FORTRAN-based) design program from the 1960s. At this time, more than 25 State DOTs have adopted SignCAD as their guide sign design program (States are dropping GuideSign and replacing it with SignCAD.) DOT has purchased more than 100 copies of SignCAD.
   5. State: Our manual (not a State MUTCD) references other standards.
   6. City: No.
   7. County: Our policies are generally consistent with our State agency.
   8. County: No.
   9. City: See general comment.

STREET-NAME SIGN SURVEY RESPONSES

This section provides the detailed responses submitted by respondents to each question in the street-name sign portion of the e-mail survey.

General Comments

1. State: None.
2. State: None.
3. State: None.
4. State: None.
5. State: None.              
6. City: None.              
7. County: Incidentally, we estimate as much as 40 percent of our total number of signs are street-name signs, so take it easy on us when it comes to any proposed changes or retroreflectivity requirements!
8. City: None.

7. What is your agency's policy for providing street-name signs (under what conditions are street-names signs provided and where are they located)?

1. State: We provide advance street-name sign for all intersections. We place street-name signs only at signalized intersections. Local agencies will install ground-mounted street-name signs at nonsignalized intersections under the encroachment permit.
2. State: For all signalized intersections, we place street-name signs on the signal support over the roadway between the support pole and the right-lane signal for each direction. If it intersects a road with two names, one to the right and one to the left, we mount the left street-name sign on the left side of our highway and the right street-name sign on the right side of our highway. For nonsignalized intersections, we replace the existing street-name signs installed by the local agency and replace "in kind" what was existing.
3. State: All roads have corner street-name signs typically installed by the local jurisdiction (located near left and far right corners of an intersection). This was a statewide initiative effort by the 911 emergency coordinators. All signalized intersections, multilane streets, and/or streets leading to major traffic generators have additional advance and/or overhead street-name signs.
4. State: Our agency does not fabricate or install "slat" street-name signs. These signs are installed by local road authorities within incorporated areas. In rural areas where street-name signs are installed for the 911 emergency telephone system, the authority in charge of the road intersecting the State highway is responsible for fabricating, installing, and maintaining the signs (we have a written guideline for 911 signing). Street-name signs (slat signs) may be made from type I, type III, or VIP sheeting, depending on how progressive communities are and how tight their budgets are. The size of the lettering varies from community to community. DOT does not regulate legend size, although the Federal MUTCD adopted (in a final rule) the 6-inch capital or 6-inch uppercase/4.5-inch lowercase FULLY REFLECTORIZED sign guidelines more than 2 years ago. The only street-name signs at intersections that our agency installs are overhead traffic signal mast-arm-mounted signs. These signs use VIP reflective sheeting with 8-inch uppercase and 6-inch lowercase Series E (Modified) letters. We use an 18-inch-high sign panel when the posted speed is less than 45 mph and a 24-inch-high sign panel for posted speeds of 45 mph or greater.
5. State: Street-name signs are a local responsibility.
6. City: Provided at all intersections at one corner of the intersection or on signal mast-arm poles.
7. County: In residential areas, we install a combination street-name sign assembly on the far right-hand quadrant in one direction of the major street. At major intersections, we often install street-name signs on two quadrants diagonally opposite.
8. County: Street-name signs are provided at intersections and along roads where name changes occur. On our local roads (non-arterials), we typically only install the street-name sign for the intersecting street, not the street you are traveling on if you have already seen that street name. This minimizes the amount of double street-name signing at intersections. We are complying with the MUTCD requirement for 6-inch letters on roads with speed limits greater than 25 mph. We are also using 6-inch letters on 25-mph arterials, but are still using 4-inch letters for local (non-arterial) roads.
9. City: We require that street-name signs be installed at every intersection. At signalized intersections, we install 18-inch-deep signs on the mast arm. The length varies with the number of letters. At nonsignalized intersections, we try to install the signs over the STOP signs to eliminate the intrusion of an extra post on a person's property and to help us out by saving a post. We install 12-inch-deep signs at all of these locations. We now use diamond-grade VIP sheeting on all street-name signs. They are made in our shop by cutting green vinyl over silver sheeting.

1. State: Street-name signs at signalized intersections are overhead, at a minimum height of 15 ft. Ground-mounted advance street-name signs are 7 ft where pedestrians may be present, otherwise 5 ft. Street-name signs placed by the locals are approximately 11 to 12 ft.
2. State: Minimum of 17 ft for signalized intersections. For nonsignalized intersections, used the MUTCD requirements.
3. State: 7-ft minimum for ground-mounted signs. Height may vary depending on whether the corner signs are combined with STOP signs on the same support. 17-ft minimum for overhead applications on signal structures.
4. State: See response to question 7.
5. State: 7 ft above the sidewalk or pavement.
6. C ity: 7 ft.
7. County: Approximately at a 10-ft mounting height.
8. County: 7 ft nominal to bottom of sign.
9. City: A minimum of 7 ft, if installed alone on a separate post. If above a STOP sign, the minimum height would be approximately 9.5 ft, and if on a mast arm, approximately 20 ft.

1. State: The standard color is a green background with a white border and legend.
2. State: Our agency uses a green background for signalized intersections. For nonsignalized intersections, we use the existing color. Green or blue background, or special color for historical areas.
3. State: Typically, a white legend on a green background. They are black legend on yellow background when placed in combination with advance warning signs.
4. State: See response to question 7.
5. State: Our regulations allow white on green, black on white, or other contrasting colors. I'd have to say that most are white on green.
6. City: White legend on green background.
7. County: White on green.
8. County: White letters on green background.
9. City: Green background with white border and letters.

1. State: Standard blank size for overhead street-name sign is 18 by 96 inches (maximum width).
2. State: For signalized intersections, the maximum sign panel height is 18 inches and the length is 7 ft.
3. State: Typically 8 inches high by a variable width depending on the street name for the corner blades. Typically 16 inches high by a variable width for advance and overhead street-name signs on signal structures.
4. State: See response to question 7.
5. State: 36 by 10 inches.
6. City: 9 inches (18 inches on signal mast arm).
7. County: 9 inches.
8. County: 24 by 6 inches and 30 by 6 inches on local/residential roads, 30 by 9 inches and 36 by 12 inches on arterials and all roads intersecting with arterials.
9. City: 12 inches for ground mount, 18 inches for mast-arm mount (24 inches if two street names). We just changed to the 12-inch minimum standard last year. Prior to that, we used 9 inches for arterials and 6 inches for locals.

1. State: The legend letter height is 6-inch uppercase and 4.5-inch lowercase.
2. State: Depends upon the length of the street name to fit the panel size.
3. State: Typically 4 inches for corner street blades. Typically 8-inch uppercase and 6-inch lowercase for advance and overhead street-name signs.
4. State: See response to question 7.
5. State: 6 inches.
6. City: 6 inches (10 inches).
7. County: 5-inch uppercase and 3.75-inch lowercase (will be modified to 6-inch uppercase in near future).
8. County: 4 inches on 6-inch blanks, 6 inches on 9-inch blanks, 5 inches on 12-inch blanks that require two lines of text.
9. City: The legend is usually 8-inch capital letters and 6-inch lowercase letters. We always use uppercase and lowercase layouts. The size will be reduced approximately 1 inch if the street name contains a drop in letter.

1. State: The alphabet is the Federal alphabet, Series E (Modified).
2. State: Overhead use Series E (Modified). Ground-mounted street-name signs typically use Series D.
3. State: Series C for the corner blades. Series D for the advance and overhead street-name signs.
4. State: See response to question 7.
5. State: Varies, generally Series D.
6. City: Series B and C.
7. County: Series C.
8. County: Series B or C.
9. City: We use Series C. (We did experiment with the Clearview font; however, we saw no significant difference in appearance or legibility and decided not to pursue FHWA permission.)

1. State: The background and legend reflective sheeting is high intensity, type III or IV.
2. State: Type III
3. State: Type III
4. State: See response to question 7.
5. State: Varies, but personally I believe the bulk of them are type I.
6. Ciity: Green electronic cuttable (EC) film on white high-intensity sheeting
7. County: High intensity.
8. County: Engineering grade.
9. City: When we adopted a 12-inch panel size standard, we also adopted a diamond-grade VIP sheeting standard with green acrylic overlay film.

14. Do you have any agency guidelines for the design of street-name signs that are different from that contained in your State's MUTCD? (If so, please send us a copy at your convenience.)

1. State: No, we conform to the current Federal MUTCD.
2. State: Elder Road User Program requires use of 18-inch height panel, so the letter height varies depending upon the length of the street name. Common for overhead-mounted street names. Not sure how common or practical this practice is for ground-mounted street-name signs.
3. State: Yes. Standard street-name sign details from the agency's Sign Book will be forwarded to you.
4. State: See response to question 7.
5. State: No, except we require a larger size for overhead street-name signs at signalized intersections.
6. City: No response.
7. County: Policy of 1988 is being updated.
8. County: No.
9. City: No.

APPENDIX B. MODELING PROCESS

This section of the report was provided to further document the details pertaining to the development of the MR levels. By going through the process, this section also provides a good example of why different sheeting types require different MR levels.

For ease of explanation, it is helpful to consider a specific example. For instance, table 40 shows the MR levels for overhead guide signs. For the white sheeting, there are sheeting types that are not allowed, and of the sheeting types that do have MR numbers, the levels depend on the sheeting type. The development of these findings is detailed in the following discussion.

The first issue to be considered is the position of the sign relative to the driver. For the conditions under which the MR levels were developed, the overhead guide sign was 640 ft from the vehicle. The centroid of the sign was located 25 ft above the pavement surface and was centered above the left adjacent lane of the travel lanes (both lanes were 12 ft wide). The vehicle used was a passenger car. Both the right and left headlamps were the CARTS50 headlamps.

Table 41. Overhead Sign Example

This is enough information to determine the angles and the amount of light reaching the sign. Table 41 shows the important levels.

As seen from table 41, the observation angle for the left headlamp is 0.152° and the entrance angle is 2.24°. These are obviously not the same as the standard measurement geometry of 0.2° and -4.0° (for the observation and entrance angles, respectively). Instead, these are the exact angles of the scenario defined above. In other words, they can be considered nonstandard geometry.

As noted in chapter 4, there are only two basic equations needed to determine the MR. They are shown below:

                                                           (3)

                                                       (4)

where,.

Minimum R_A           =          MR at standard measurement geometry ( = 0.2°, = -4.0°) needed to produce assumed threshold luminance, cd/lx/m²

New R_A,SG                  =          Averaged retroreflectivity of new sheeting at standard geometry, cd/lx/m²

Demand R_A,NSG =          Retroreflectivity needed to produce the minimum luminance at the nonstandard geometry (backcalculated and determined for each scenario), cd/lx/m²

Supply R_A,NSG =          Retroreflectivity of new sheeting at nonstandard geometry (determined for each scenario), cd/lx/m².

One of the most significant unknowns prior to this research was the minimum luminance needed in equation 3. The field evaluations conducted as part of this study were designed to determine the minimum luminance for overhead guide signs and street-name signs, with an emphasis on accommodating older drivers. The results are summarized in table 18. For the 50^th percentile accommodation level, the minimum luminance for overhead signs was 2.3 cd/m².

The next step is to determine how much retroreflectivity is needed to produce a luminance of 2.3 cd/m². There are two key issues to be considered. First, the vehicle in this scenario is 640 ft from the sign and, as shown, the angles associated with the scenario do not correspond to the standard measurement geometry. Therefore, the retroreflectivity needed to produce a luminance value of 2.3 cd/m² at 640 ft from the sign is termed the demand retroreflectivity at the nonstandard measurement geometry (Demand R_A,NSG).

Second, the minimum luminance (which can also be thought of as the demand luminance because that is what is being demanded of the sheeting) is really the total luminance. In other words, it is a combination of the luminance provided by both the left and right headlamps. However, it cannot be simply halved for each headlamp because each headlamp contributes differently to the total luminance. The difference is explained by the different angles for each headlamp, which impact the following factors:

1. Amount of light directed to the sign (luminous intensity).
2. Amount of light reaching the sign (illuminance).
3. Performance of the sheeting (retroreflectivity).

To determine the contribution that each headlamp makes toward the demand luminance, the supplied luminance of the sign is determined for new sheeting. First, the luminance provided by each headlamp is determined (row 3 of table 42), then the total luminance is found by summing the luminance of each headlamp (row 4 of table 42). Using these values, the contribution of each headlamp can be determined. This is shown in row 5 of table 42.

Using the contribution from each headlamp and the demanded luminance value (2.3 cd/m² in this case), one can determine the demand retroreflectivity at the nonstandard measurement geometry (Demand R_A,NSG). This is done using equation 3. The results are shown in row 6 of table 38.

The next step is to determine the supplied retroreflectivity at the nonstandard geometry. Using the angles shown in table 41 and the large databases of sheeting performance (one for each type of sheeting), it is possible to determine the retroreflectivity levels of each type of sheeting at the nonstandard geometry. This was done for each headlamp geometry. The values are shown in row 7 of table 42. The next step is to determine whether the sheeting provides enough luminance to meet the desired or demanded luminance (in this case, 2.3 cd/m²). This step includes several substeps. The first is to use the luminance produced by each type of new sheeting (row 8 of table 42). The summed luminance can be considered the raw luminance. This is the ideal luminance. However, at least two factors reduce the luminance as viewed by a driver. The first is the windshield. A typical value for windshield transmissivity is 0.72, although this can vary slightly with different windshields. The second reduction factor is caused by the atmosphere. An atmospheric transmissivity of 0.86/km was used here, which represents a typical dry day. The result of these reductions in luminance is the luminance supplied to the driver (row 10 of table 42). Finally, in row 11 of table 42, a check is made to ensure that the different types of sheeting supply enough luminance to meet the demand. If a particular type of sheeting does not meet the demand luminance, then it cannot provide sufficient luminance for the scenario even when unweathered. In this case, sheeting types I and II cannot supply enough luminance to meet the demand of 2.3 cd/m².

Now that the adequate sheeting types are identified, the next step is to determine the MR needed for each sheeting type. This is accomplished using equation 4. The results are shown in row 13 of table 42. Because headlamp contribution was accounted for earlier in the process, the retroreflectivity for each headlamp is the same.

The final step was a simple rounding of the numbers to the nearest value divisible by five. The results, shown in row 14 of table 42, are the MR levels for overhead guide signs at the standard measurement geometry. When the sheeting falls to these values, the luminance provided to a motorist at 640 ft from an overhead sign positioned as indicated will be 2.3 cd/m².

Retroreflectivity values higher than those shown in row 14 of table 42 will produce luminance values higher than 2.3 cd/m². The highest luminance value a sheeting can supply a driver when the sheeting is unweathered is shown in row 10 of table 42 (for the conditions given in this example).

Table 42. Example MR Calculations

1	ASTM sheeting designation	Type I		Type II		Type III		Type VII		Type VIII		Type IX
2	Headlamp position	Left	Right	Left	Right	Left	Right	Left	Right	Left	Right	Left	Right
3	Luminance per headlamp with new sheeting (cd/m2)	1.13	0.77	1.97	1.26	3.66	2.30	13.21	7.45	11.31	7.75	7.30	4.68
4	Total RAW supplied luminance (cd/m2)	1.90		3.23		5.97		20.66		19.06		11.98
5	Contribution from each headlamp (%)	59.4	40.6	61.1	38.9	61.4	38.6	64.0	36.0	59.3	40.7	60.9	39.1
6	Demand RA @ NSG (cd/lx/m2)	125.1	87.4	128.8	83.6	129.4	83.0	134.8	77.5	125.0	87.5	128.3	84.1
7	Supply RA @ NSG (cd/lx/m2)	104.2	72.86	182.1	118.1	337.8	216.8	1218.2	701.0	1043	730.0	672.7	440.9
8	Total RAW supplied luminance (cd/m2)	1.90		3.23		5.97		20.66		19.06		11.98
9	Reduction: Windshield transmissivity (0.724) and atmospheric transmissivity (0.86/km)	0.74		1.26		2.34		8.08		7.45		4.69
10	Total supplied luminance (cd/m2)	1.16		1.97		3.63		12.58		11.61		7.29
11	Check: Luminance adequacy (2.3 vs. row 10)	Inadequate		Inadequate		Adequate		Adequate		Adequate		Adequate
12	New RA @ SG (cd/lx/m2)	97.1	97.1	169.6	169.6	314.4	314.4	1190.1	1190.1	822.6	822.6	433	433
13	Minimum RA @ SG (cd/lx/m2)					120.4	120.4	131.6	131.6	98.6	98.6	82.6	82.6
14	Rounded Minimum RA @ SG (cd/lx/m2)					120		130		100		85
NSG = nonstandard measurement geometry ( ≠ 0.2° and ≠ -4.0°) SG = standard measurement geometry ( = 0.2° and = -4.0°)

REFERENCES

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