Flashing-Light Signals

The fundamental active warning device is the flashing ‑light signal, refer to Figure 21, which shows the unit combined with an automatic crossing gate. Flashing-light signals consist of two light units that flash alternately at a rate of 35 to 65 times per minute. The signal lens is red and comes in a variety of designs that direct the light toward the motorist. The lamp consists of a low-wattage bulb (legacy units) or LED assembly (current practice) used to ensure operation on stand-by battery power should commercial power fail. The LED units used in new installations offer many advantages over conventional incandescent lamps including the following:

•Higher visibility at greater distances for in-line observations

•Greater visibility on angles

•Wider beam pattern and therefore easier beam alignment

•Pure red signal with fast on/off transition, which improves conspicuity

•Lower current consumption at nominal voltage, thereby suitable for solar-powered applications

•Longer life expectancy Figure 21. Illustrative Example Showing Cantilever with Flashing-Light Devices Source: Brent Ogden. 56Key MUTCD requirements (refer to Part 8C.02) include the following:

•If used, the flashing ‑light signal assembly on the side of the highway shall include a standard Crossbuck (R15-1) sign, and, where there exists more than one track, a supplemental Number of Tracks (R15-2P) plaque, all of which indicate to motorists, bicyclists, and pedestrians the location of a crossing.

•The flashing ‑light signal shall display toward approaching highway traffic two red lights mounted in a horizontal line flashing alternately.

•Flashing ‑light signals shall be placed to the right of approaching highway traffic on all highway approaches to a crossing. They shall be located laterally with respect to the highway in compliance with MUTCD Figure 8C-1 except where such location would adversely affect signal visibility.

•If used at a crossing with highway traffic in both directions, back ‑to‑back pairs of lights shall be placed on each side of the tracks. On multi ‑lane one ‑way streets and divided highways, flashing ‑ light signals shall be placed on the approach side of the crossing on both sides of the roadway or shall be placed above the highway.

•MUTCD requires 12-inch lenses for all new installations excepting signals controlling pedestrian movements; however, where 8-inch units are already in place they may be retained for the remainder of their useful service life. Other MUTCD guidance includes the following:

•At highway-rail crossings, bells or other audible warning devices may be included in the assembly as determined by a Diagnostic Team and may be operated in conjunction with the flashing ‑lights to provide additional warning for pedestrians, bicyclists, and/or other non ‑ motorized road users.

•If determined by a Diagnostic Team, flashing ‑light signals may be installed on overhead structures or cantilevered supports, as shown in Figure 21, where needed for additional emphasis, or for better visibility to approaching traffic, particularly along multi ‑lane approaches or highways with profile restrictions. If it is determined by a Diagnostic Team that one set of flashing ‑lights on the cantilever arm is not sufficiently visible to road users, one or more additional sets of flashing ‑ lights may be mounted on the supporting post and/or on the cantilever arm. Current practice is to provide one flashing ‑light signal directed at each approach lane which may require use of an overhead cantilever and to provide supplemental flashing ‑light units aimed at frontage road approaches, as discussed below. Proper alignment of the light is essential. The following guidance on aiming lights was developed originally for highly directional 12 ‑volt bulbs and reflectors. Current LED equipment, however, is more tolerant on the precision of aiming. Nevertheless, the aiming principles described should be followed. The flashing ‑light unit on the right ‑hand side of the highway is usually aligned to cover a distance far from the crossing. The light units mounted on the back of the signals on the opposing approach and, thus, on the left, are usually aligned to cover the near approach to the crossing. Figure 22 shows typical alignment patterns for a two-lane, two-way highway and for a multilane highway. Figure 22. Typical Alignment Pattern for Flashing-Light Signals with 30–15 Degree Roundel, Two-Lane, Two-Way Roadway Source: Communications & Signals Manual, Figure 335-1, Lanham, MD, AREMA, 2018.

Cantilevered Flashing-Light Signals

Flashing ‑light signals are post ‑mounted, but where improved visibility to approaching traffic is required, cantilevered flashing ‑light signals are used. Cantilevered flashing ‑lights may be appropriate when any of the following conditions exist:

•Multilane highways (two or more lanes in one direction)

•Highways with paved shoulders or a parking lane that would require a post-mounted light to be more than 10 feet from the edge of the travel lane

•Roadside foliage obstructing the view of post ‑mounted flashing ‑light signals

•A line of roadside obstacles such as utility poles (when minor lateral adjustment of the poles would not solve the problem)

•Distracting backgrounds such as an excessive number of neon signs (conversely, cantilevered flashing ‑lights should not distract from nearby highway traffic signals)

•Horizontal or vertical curves at locations where the extension of flashing ‑lights over the traffic lane will provide sufficient visibility for the required stopping sight distance 58A typical installation consists of one pair of cantilevered lights on each highway approach, supplemented with a pair of lights mounted on the supporting mast. However, two or more pairs of cantilevered flashing ‑lights may be desirable for multilane approaches, as determined by an engineering study. The cantilevered lights can be placed over each lane so that the lights are mutually visible from adjacent driving lanes. Most current installations utilize walkout cantilevers. The inclusion of a ladder and access walkway allows for easier maintenance with less impact to highway traffic. Standard cantilevers for mounting flashing ‑lights are made with arm lengths up to 40 feet. Where cantilever arm length is more than 35 feet, a bridge structure is preferred.

Supplemental Flashing-Light Signals

Additional pairs of light units, sometimes referred to as “side lights” may also be installed for side roads intersecting the approach highway near the crossing or for horizontal curves. Figure 23 shows the use of multiple pairs of lights to cover a horizontal curve to the left on the approach highway. A horizontal curve to the right may be covered by placing another roadside flashing ‑light unit on the opposite side of the highway, as shown in Figure 24. Figure 25 shows the use of side lights to provide warning to road users approaching from frontage roadways parallel the railroad. Mounting of angled side light units should maintain the 30-inch spacing indicated in MUTCD Figure 8C-1 from the vantage point of the road user. Figure 23. Use of Multiple Flashing-Light Signals for

Adequate Visibility Horizontal Curve to the Left

Source: Institute of Transportation Engineers. Figure 24. Use of Multiple Flashing-Light Signals for

Adequate Visibility Horizontal Curve to the Right

Source: Institute of Transportation Engineers. Figure 25. Use of Sidelights for Frontage Roads Source: Institute of Transportation Engineers.