CEMP-E
TI 850-02
AFMAN 32-1125(I)
1 MARCH 2000
f. Track Design.
(1) As with other crossing surfaces, prefabricated concrete crossings do not act alone - their
performance depends on adequate support from the ballast and subgrade. Unless recently done, the
track, ballast section, and drainage system must first be rebuilt on a well-prepared subgrade before
installing the crossing. The drainage system must effectively transmit water outside the crossing limits.
(2) When crossings are built or rebuilt, all the ties in the crossing itself and for at least 20 ft beyond
each end of the crossing should be replaced. It is recommended that wood ties used in road crossings
be 7 x 9-in. in cross section. When prefabricated road crossings are installed, tie length and spacing
should conform with the installation requirements provided by the crossing manufacturer.
(3) For road crossings having heavy volumes of rail traffic and heavy vehicle traffic, it may be
desirable to install tie pads beneath the tie plates in the crossing area, as shown in figure 7-15. With
concrete panel crossings, full length pads should always be nailed to the ties with 1-in. roof nails to
properly support the panels; most manufacturers recommend this and supply the pads with the crossing
panels.
Figure 7-15. Recommended Track Construction for Road Crossings
(4) In crossings on main running tracks, rail of 115 lb per yd or greater is preferred.
(5) As bolted rail joints in road crossings are often a maintenance problem, it is recommended that all
joints through the crossing and for 20 ft from either end of the crossing be welded. As an alternative, 80-ft
rails are readily available and may be used to eliminate joints in the crossing area.
7-18
Previous Page
