1. The following conditions will reduce the ratings from those given above. The
bridge commander must monitor bow and roadway freeboard as well as trim
to ensure that safe crossing conditions are maintained in the following
BRIDGE OPERATION (Contd)
(a) Rough, choppy, or turbulent water in current speeds above 4 feet/sec (1.2
meters/sec) will reduce ratings from those given in the preceding chart.
(b) Shallow fast water of less than 6 ft 7 in (2.0 m) water depth combined with
current speeds above 4 feet/sec (1.2 meters/sec) will reduce the ratings from
those given the preceding chart.
(c) Accumulations of snow, mud, or ice will reduce the ratings from those given
2. Bridge commander must observe leading edge of bridge and decrease crossing
rating (Normal to Caution to Risk) or halt operations, as necessary, if
continuous water is coming over bow dam.
3. These ratings apply for a bridge held in place with Mk I/II bridge erection boats
BEBs). The number of bays that boats are to be spaced apart is based on the
current speed and is as follows:
Note: If the bridge is to remain in place for long periods or time, an anchorage
system shall also be used.
4. Vehicle spacing:
Normal and two-lane (each lane): 100 ft (30 m) front to back
170 ft (52 m) front to back
Only one vehicle on bridge at a time
NUMBER OF BAYS PER MK I/II BEB
0.05.0 feet/sec (0.01.5 meters/sec)
5.08.0 feet/sec (1.52.4 meters/sec)
8.09.0 feet/sec (2.42.7 meters/sec)
9.010.0 feet/sec (2.73.0 meters/sec)
Anchorage system necessary
Table 4. Improved Ribbon Bridge Operation BEB Spacing.