Retroreflectivity (MUTCD Table 2A-3)
The MUTCD provides suggestions for methods to be used:
- 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 acceptable level should be replaced.
- Measured Sign Retroreflectivity - Sign retroreflectivity is measured using a retroreflectometer. Signs with retroreflectivity below the minimum acceptable level should be replaced.
- 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 acceptable level. Signs older than the expected life should be replaced.
- 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.
- 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 acceptable level.
Other Methods - Other methods developed based on engineering studies can be used.
Roadside Placement (MUTCD, Figure 2A-2)
For a typical rural road with no shoulder, the sign should be placed on the right side of the roadway, 12 feet laterally from the edge of the traveled way. In terms of vertical height, the bottom of the sign should be installed 5 feet above the ground elevation at the edge of pavement.
Enhancing Sign Conspicuity Cost Effectively (MUTCD Figure 2A-1)
In a situation where it is desirable to enhance a sign's conspicuity, any of the following methods may be used:
- Increasing the size of the sign;
- Doubling-up by adding a second identical sign on the left hand side of the roadway; or
- Adding a strip of retroreflective material to the sign support.
Regulatory Signs and Markings
Stop Sign (R1-1)
The minimum size for a STOP sign shall be 30" x 30" for a typical rural, two-lane facility.
Stop bars shall be a solid white line.
Stop bars should be 12-24" wide.
The stop line should be placed at the desired stopping or yielding point, but should not be placed more than 30 feet or less than 4 feet from the nearest edge of the intersecting traveled way.
Markings should be visible at night by use of retroreflectivity or ambient illumination (Section 3A.03).
The MUTCD specifies allowable colors for pavement markings and the function of each color. (Section 3A.05).
To avoid confusion to the road user, pavement markings should be placed according to the MUTCD, and pavement markings which are no longer applicable should be removed (Section 3A.02)
When to use
The use of warning signs shall be based on an engineering study or on engineering judgment.
Warning signs should be installed in advanced of the intersection in accordance with Table 2C-4, which provides placement distances based on speed.
Stop Ahead (W3-1)
30" x 30" minimum
These signs shall be installed on an approach to a STOP sign that is not visible for a sufficient distance to permit the road user to respond to the device.
To be used only on the "side road" that must come to a stop.
Intersection Ahead (W2-1, W2-2, W2-3, W2-4)
30" x 30" minimum
The Intersection Warning sign should illustrate and depict the general configuration of the intersecting roadway, such as cross road, side road, T-intersection, or Y-intersection.
Advisory Speed Plaque (W13-1P)
18" x 18"
The sign height changes when a speed plaque is added. See Figure 2A-2, Page 38, for details.
Two-Direction Large Arrow (W1-7)
48" x 24"
The two-direction large arrow shall be installed on the far side of a T-Intersection in line with, and at approximately a right angle to, traffic approaching from the stem of the T-intersection.