(6) In certain circumstances, the engineers may decide to use
special signs. This is often the case in bridges over class 50, since those
may be used by the larger tracked vehicles.
In those cases, a separate
classification is indicated for wheeled and tracked vehicles. For a one-way
bridge, the circle will be divided horizontally. The upper half will tell
you the wheeled classification and the lower the tracked.
They normally
contain a silhouette of a wheeled and tracked vehicle, respectively, to
prevent confusion.
In some cases, it may be desirable to show different
classifications for wheeled and tracked vehicles on a two-way bridge. This
is done by using two circles, one above the other. The top symbol provides
the information for wheeled vehicles and the lower for tracked.
(7) You have spent a great deal of time dealing with bridge
symbols. This is because they are normally the weakest link in the route.
Therefore, in the route classification formula, the lowest bridge
classification number is entered. This is regardless of the vehicle type or
condition of traffic flow. The smallest number provides the classification
for the entire route.
When there are no bridges on the route, the worst
section of the road sets the route classification.
(8) Classifying the route this way keeps it from being
overloaded. When vehicles have a higher load classification than the route,
the engineers conduct a special recon to determine if it can still be used.
They might determine that a two-way route could be used at a higher
classification if it was changed to one-way. They may also determine that a
risk crossing is possible.
(9) Posting of the bridge signs needed for proper control of
traffic across a bridge is an engineer responsibility.
Special signs are
used when necessary to warn vehicles of unusual conditions. When necessary,
holding areas, turnouts for parking and unloading, and checkpoints are
installed near bridges.
Traffic control measures are outlined in the
traffic circulation plan and the traffic control plan of the area commander.
e.
Overhead Clearance.
The next entry in the route classification
formula indicates the overhead clearance.
The overhead clearance is the
distance between the road surface and any obstruction above it that
restricts traffic flow. It is the clearance that you often see on bridges
and overpasses. Vehicles over a certain height, cannot use the road. Some
examples are overpasses, tunnels, overhead wires, overhanging buildings, and
old city gates. If the clearance on the route is unlimited, the symbol is
used.
Overhead clearance is considered an obstruction if it is less than
4.3 meters (14 feet).
Whatever the overhead clearance, it is noted.
As
with the other categories of information, the lowest clearance on the route
is the one which is listed.
f.
Obstructions. If there are any obstructions on the route, they
are indicated in the formula by the symbol "OB." Anything that restricts the
type, amount, or speed of the traffic flow is considered an obstruction.
The only exception is bridges.
Bridges are considered only in the route
classification.
Recon symbols are used to show the nature of the
obstruction
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MP1028
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