CEMP-E
TI 850-02
AFMAN 32-1125(I)
1 MARCH 2000
(3) Traffic Character and Volume. Additional protection may be desirable at crossings that
experience two or more train movements per day and the product of train movements and average daily
vehicle traffic exceeds 3,000. This traffic threshold drops to 1,000 for crossings that are considered
visually obstructed, as defined above. Flashing lights (or even gates) should be considered for crossings
that experience several daily train movements, have heavy truck traffic or frequent hazardous material
traffic, and where clear visibility criteria are not met.
(4) Crossing Geometry. Crossings with a road to track angle of less than 45 degrees, or where the
road approaches the track at a steep grade, may call for additional protection.
(5) Accident and Incident History. Crossings that have experienced at least one serious accident,
some close-call incidents, and/or where incidents of motorists not obeying existing warnings are common,
should at least receive consideration for flashing lights, or gates if flashing lights are already present.
i. Whistle Posts.
(1) General. Whistle posts are signs located adjacent to the track to indicate that a road crossing is
ahead. They mark the point at which the standard horn signal for crossing approach must begin. Whistle
posts commonly show just a large letter "W" on their face, but various designs have been used. The
installation's operating rules may designate the type of sign required.
(2) Location. Whistle posts are usually located on the right side of the track (when viewed facing the
crossing) at a distance that allows sufficient time to warn motorists that an engine, train, or track machine
is approaching the crossing. Designers should consult the state Department of Transportation and the
installation for requirements on whistle post location. The appropriate location will depend on factors that
include the speed of railroad traffic, speed of vehicle traffic, and the visibility at the crossing. A commonly
used guideline is that the crossing warning signal must begin sounding at least 20 seconds before an
engine, car, or track machine reaches the nearest end of the crossing.
2. BRIDGES.
a. Types. Railroad bridges may be classified by deck type: open deck or ballast deck. In a typical open
deck bridge, every fourth tie is bolted directly to the structure; thus in effect, the track becomes part of the
bridge. In a ballast deck bridge, a standard track and ballast section are supported on a solid floor. The
ballast deck has the advantage of allowing the track across the bridge to be lined and surfaced in the
same fashion as standard track.
b. Design Procedures. When a bridge is required, the bridge structure will be designed by a practicing
railroad bridge engineer in accordance with the AREMA Manual: chapter 7 for timber structures, chapter
8 for concrete structures, or chapter 15 for steel structures. Part 9 of AREMA chapter 15 provides
background and commentary on railroad bridge design practices.
c. Basis for Design. The design of railroad bridges is based on two main factors: the magnitude of
loads applied to the bridge and the expected level of traffic (or number of stress cycles) over the design
life of the bridge. One stress (or load) cycle is defined by one application and release of loading on a
bridge member.
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