2 Del. Admin. Code § 4D.12
Current through Register Vol. 28, No. 5, November 1, 2024
Section 4D.12 - Visibility, Aiming, and Shielding of Signal FacesStandard:
01 The primary consideration in signal face placement, aiming, and adjustment shall be to optimize the visibility of signal indications to approaching traffic.02 Road users approaching a signalized intersection or other signalized area, such as a midblock crosswalk, shall be given a clear and unmistakable indication of their right-of-way assignment.03 The geometry of each intersection to be signalized, including vertical grades, horizontal curves, and obstructions as well as the lateral and vertical angles of sight toward a signal face, as determined by typical driver-eye position, shall be considered in determining the vertical, longitudinal, and lateral position of the signal face. Guidance:
04 The two primary signal faces required as a minimum for each approach should be continuously visible to traffic approaching the traffic control signal, from a point at least the minimum sight distance provided in Table 4D-2 in advance of and measured to the stop line. This range of continuous visibility should be provided unless precluded by a physical obstruction or unless another signalized location is within this range.05 There should be legal authority to prohibit the display of any unauthorized sign, signal, marking, or device that interferes with the effectiveness of any official traffic control device (see Section 11-205 of the "Uniform Vehicle Code").06 At signalized midblock crosswalks, at least one of the signal faces should be over the traveled way for each approach. Standard:
07 If approaching traffic does not have a continuous view of at least two signal faces for at least the minimum sight distance shown in Table 4D-2, a sign (see Section 2C.36) shall be installed to warn approaching traffic of the traffic control signal. Option:
08 If a sign is installed to warn approaching road users of the traffic control signal, the sign may be supplemented by a Warning Beacon (see Section 4L.03).09 A Warning Beacon used in this manner may be interconnected with the traffic signal controller assembly in such a manner as to flash yellow during the period when road users passing this beacon at the legal speed for the roadway might encounter a red signal indication (or a queue resulting from the display of the red signal indication) upon arrival at the signalized location. | Table 4D-2. Minimum Sight Distance for Signal Visibility |
| 85th-Percentile Speed | Minimum Sight Distance | |
| 20 mph | 175 feet | |
| 25 mph | 215 feet | |
| 30 mph | 270 feet | |
| 35 mph | 325 feet | |
| 40 mph | 390 feet | |
| 45 mph | 460 feet | |
| 50 mph | 540 feet | |
| 55 mph | 625 feet | |
| 60 mph | 715 feet | |
| Note: Distances in this table are derived from stopping sight distance plus an assumed queue length for shorter cycle lengths (60 to 75 seconds). | |
10 If the sight distance to the signal faces for an approach is limited by horizontal or vertical alignment, supplemental signal faces aimed at a point on the approach at which the signal indications first become visible may be used. Guidance:
11 Supplemental signal faces should be used if engineering judgment has shown that they are needed to achieve intersection visibility both in advance and immediately before the signalized location.12 If supplemental signal faces are used, they should be located to provide optimum visibility for the movement to be controlled. Standard:
13 In cases where irregular street design necessitates placing signal faces for different street approaches with a comparatively small angle between their respective signal indications, each signal indication shall, to the extent practical, be visibility-limited by signal visors, signal louvers, or other means so that an approaching road user's view of the signal indication(s) controlling movements on other approaches is minimized.14 Signal visors exceeding 12 inches in length shall not be used on free-swinging signal faces. Guidance:
15 Signal visors should be used on signal faces to aid in directing the signal indication specifically to approaching traffic, as well as to reduce "sun phantom," which can result when external light enters the lens.16 The use of signal visors, or the use of signal faces or devices that direct the light without a reduction in intensity, should be considered as an alternative to signal louvers because of the reduction in light output caused by signal louvers. Option:
17 Special signal faces, such as visibility-limited signal faces, may be used such that the road user does not see signal indications intended for other approaches before seeing the signal indications for their own approach, if simultaneous viewing of both signal indications could cause the road user to be misdirected. Guidance:
18 (DE Revision) Backplates should be used to supplement all vehicular signal heads mounted on mast arms and where an engineering study indicates their need to resolve a problem such as where sun glare, bright sky, and/or complex or confusing backgrounds indicate a need for enhanced signal face conspicuity. Support:
19 (DE Revision) The use of backplates enhances the contrast between the traffic signal indications and their surroundings for both day and night conditions, which is also helpful to older drivers. Signal backplates with a retroreflective border provide additional conspicuity for signal heads and providing backplates on mast-arm-mounted signal heads does not require additional tethering. Standard:
19A 19A (DE Revision) If backplates are installed, they shall include a two-inch wide yellow retroreflective border.19B 19B (DE Revision) If backplates are installed on a span wire, a tether wire shall also be used.20 The inside of signal visors (hoods), the entire surface of louvers and fins, and the front surface of backplates shall have a dull black finish to minimize light reflection and to increase contrast between the signal indication and its background. Option:
21 A yellow retroreflective strip with a minimum width of 1 inch and a maximum width of 3 inches may be placed along the perimeter of the face of a signal backplate to project a rectangular appearance at night.2 Del. Admin. Code § 4D.12
21 DE Reg. 905 (5/1/2018) (Final)