Audible Warning
A crossing bell is an audible warning device used to supplement other active traffic control devices. A bell is most effective as a warning to pedestrians and bicyclists. When used, the bell is usually mounted on top of one of the signal support masts. Alternatively, the bell may be separately mounted on an arm attached to the signal mast. The bell is usually activated whenever the flashing ‑light signals are operating. Bell circuitry may be designed so that the bell stops ringing when the lead end of the train reaches the crossing. When gates are used, the bell may be silenced when the gate arms descend to within 10 degrees of the horizontal position. Silencing the bell when the train reaches the crossing or when the gates are down may be desired to accommodate residents of suburban areas. Crossing bell specifications indicate a range of a minimum of 75 dB(A) and a maximum of 105 dB(A). AREMA specifications detail how these measurements are taken, including the following:
•Bell should operate between 100 and 325 strokes per minute.
•Electronic bells should emulate the sound of electro-mechanical bells.
•Practitioners should decide as to whether one audible device is adequate to serve the entire crossing or if a second bell should be added at large crossings. In addition to the audible device(s) provided at the crossing, FRA requires the sounding of locomotive mounted horns in advance of crossing occupancy by a train. Refer to “Requirement to Sound the Locomotive Horn” within the “Quiet Zones” topic in Chapter 6 for additional guidance.
Wayside Horn
Another form of audible warning is the wayside horn. The wayside horn system consists of a horn or series of horns located at a public highway-rail crossing and directed at oncoming motorists. (Refer to Figure 26 which shows a typical installation using two horns to alert road users approaching from each direction.) The system is designed on fail-safe principles and provides a means to verify sound output. The wayside horn system does the following:
•Simulates the sound and pattern of a train horn
•Provides similar response from road users
•Minimizes the audible footprint in comparison to a locomotive horn sounding when approaching a highway-rail crossing Figure 26. Automated Wayside Horn Source: Campbell Technology Corporation. A wayside horn system can be used as an adjunct to train-activated crossing warning systems to provide audible warning of an approaching train for traffic on each approach to the highway ‑rail crossing. Wayside horns provide a directional sound which is aimed at approaching roadway users and pedestrians while minimizing the noise impact to properties adjacent to the railroad beyond the immediate crossing zone. (The wayside horn system does not need to be directed toward approaching roadway users on roadways adjacent to the railroad if a ST OP sign or traffic signal control device controls roadway traffic.) When a wayside horn system is used at highway-rail crossings where the locomotive-mounted horn is not sounded, the highway ‑rail crossings should be equipped with flashing ‑lights and gates, power ‑ out indicator, and constant warning circuitry—where practical. In such instances, the wayside horn should also provide a “confirmation” indication to the locomotive engineer; in the absence of a confirmation signal, the engineer would need to activate the locomotive ‑mounted horn. The wayside horn system simulates a train horn and sounds at a minimum of 15 seconds prior to the train’s arrival at the highway-rail crossing, until the lead locomotive has traversed the crossing. Where multiple tracks are present, the wayside horn system is immediately reactivated when another train is detected before the previous train clears the crossing. Wayside horn systems should include a 3 ‑ to 5‑second delay after activation of flashing ‑lights signals before sounding. Section 8C.07 of the MUTCD discusses the installation of wayside horn systems in compliance with 49 CFR 222. (5) These systems provide audible warning directed toward the road users at a highway-rail or highway-LRT crossing, or at a pathway crossing. Additional information regarding Quiet Zones can be found in this Handbook in the section regarding Quiet Zones.