HIGHWAY BKIDGE LOCATION 31 
strong cross currents prevail at any boating stage or where any 
natural or artificial constriction causes a heavy tidal current and the 
necessity for additional horizontal clearance for the same degree of 
navigability is apparent. 
WIND CONDITIONS AS AFFECTING HORIZONTAL CLEARANCE REQUIRED 
Certain portions of a bay or broad river are observed as being 
comparatively quiet at nearly all seasons of the year, while other 
portions of the same waterway immediately adjacent will run white 
caps under the slightest wind. The difference in behavior at these 
points is doubtless the result of natural wind currents, and is con- 
trolled by the adjacent topography. It does not need to be empha- 
sized that greater horizontal leeway will be needed in the rough water 
to provide the same degree of safety for navigation. 
ALIGNMENT OF STREAM OR WATERWAY AS AFFECTING SIGHT DISTANCE FOR 
NAVIGATION 
The location of any bridge structure, whether over navigable 
waters or not, should avoid sudden bends or changes in the direction 
of the river channel. In the case of movable bridge spans, however, 
such a procedure is doubly essential in order to permit water craft 
sufficient sight distance so that they may be able to observe signals 
from the drawbridge operator while they are still at a considerable 
distance from the bridge. A long, straight approach is also neces- 
sary in order to enable any tug with a long tow to straighten out 
before having to attempt the crossing. 
DOCK AND WHARF RIGHTS AT THE BRIDGE HEAD 
The location should be such as to afford a minimum obstruction to 
the use of the river front for docks and wharfage. 
ANCHORAGE ABOVE THE BRIDGE SITE 
If it is possible to place the bridge structure above rather than 
below any large anchorage or group of docking facilities, there will 
result a great saving in time to both river and land traffic, a small 
saving in operation cost, and a gain as regards safety to the bridge 
structure itself. River traffic progressing up the ordinary waterway 
drops off at each point of dockage. By moving the location of any 
bridge just above any point of principal dockage, the number of 
openings is decreased and traffic over both waterway and highway is 
thus better served. Moreover, if barges are anchored at any point 
along the stream a location above them obviously eliminates the 
danger to the bridge structure, should any of these break their moor- 
ings during a flood stage on the river (this being an accident which 
happens with uncomfortable frequency). 
CONSTRICTION OF WATERWAY BY FILLED APPROACHES 
For any bridge structure constriction of the waterway is to be 
avoided on account of the tendency to increase current erosion. 
For navigable waters it has the further undesirable effect of producing 
swift water in the channel, rendering navigation that much more 
