1 MARCH 2000
(13) Type 4A Cast-in-Place Concrete Crossing. These may be best suited for track through paved
areas as for truck delivery areas along warehouses or through concrete material storage areas. This type
of crossing, though more durable than asphalt, is the most difficult of all types to remove if access to the
track is needed for maintenance.
(14) Type 4B Prefabricated Concrete Panel Crossing.
(a) General Characteristics. These are now being produced by a number of manufacturers and are
being widely adopted due to their relative strength and expected durability, ease of installation and
removal for track maintenance, and moderate cost. These crossings are not subject to decay as are
standard timber crossings and are much less subject to damage from plow blades during snow removal
operations, compared to timber, rubber, or gravel crossings. In addition, they may be most suitable to
accommodate traffic from tracked vehicles. When either track or adjacent road maintenance is required,
these crossings can be removed relatively easily, in part or whole, and replaced without damage to the
crossing material or track, and without loss of original evenness of surface. Like other crossings, though,
these require solid support to prevent panel breakage or loss of crossing surface evenness. Due to the
stiffness of the panels, these crossings are not recommended for locations where there is a pronounced
vertical curve in the track.
(b) Specifications. Design of these crossings varies with manufacturer. It is suggested that a type
be chosen with a minimum concrete strength of 5,000 psi, with guaranteed panel thickness variation
within +/- 1/8 in., with a waterproof and chemical resistant seal on panels, and with the option of epoxy
coated rebar. A warranty of crossing performance should also be obtained.
(c) Installation Options. In a standard or lagged installation, the panels are "lagged" (attached) to
wood ties with lag bolts, with no fastening between adjacent panels - similar to the way a conventional
timber crossing is installed. With a lagless installation, the field panels and gage panels are fastened
lengthwise to form three monolithic panels for the length of the crossing, with no fastening into the ties.
Different methods are used for panel-to-panel fastening. End angles or other end restraint devices must
be used to secure the crossing longitudinally. Vertical and lateral movement is prevented by the weight of
the fastened panels combined with confinement between the adjacent roadway and the rail for field
panels, and confinement between the rails for gage panels. With a lagless installation, flangeway fillers
must be used to keep gage panels secured away from the running rails. For most military applications,
lagless installation is suggested. Figure 7-12 shows a lagless concrete panel crossing in which adjacent
panels are fastened by a series of short welds.