HIGHWAY BRIDGE LOCATION 
25 
HORIZONTAL ALIGNMENT 
The above has to do with vertical alignment only. As regards 
horizontal alignment, bridge structures should always be located on 
tangent unless absolutely unavoidable. 
The building of handrails on curved alignment either in concrete or in timber 
requires more difficult framing, more difficult and expensive form work, and is 
consequently more costly. For timber rails, it is also much more difficult to 
maintain true alignment on account of the buckling tendency owing to the 
shrinkage and warping of the timber. 
For concrete structures, superelevation on curves necessitates that the form 
work for each panel be different, thus increasing the labor cost and resulting 
in a higher unit price. 
For covered truss spans, the question of sight distance enters. Under no 
circumstances should a covered bridge be built on any alignment which is not 
tangent entirely across the structure and for a distance of preferably not less 
than 200 feet, and in no case less than 100 feet at either end of the bridge. 
END OF BRIDGE 
CHORD GRADE 
END Of BRIDGE 
CHORD GRADE 
Fig. 23.— Treatment of bridge rails where horizontal curvature requires super- 
elevation. The treatment shown in A is the most desirable if the camber per- 
mits, but that shown in B may be necessary if fhe camber is small. 
STRUCTURES ON CURVES 
The maximum length for the individual spans in any bridge which 
should be built on any curve is given by the expression L=-t=T 
where L = length of span and D = degree of curvature. 
Where it is impossible to eliminate curvature on a bridge and where 
superelevation must be provided, each side should be treated sepa- 
rately, as shown in Figure 23, A, in such manner that both rails will 
take a continuous convex curve from end to end. Where there is 
sufficient camber to allow it, the treatment shown (fig. 23, A) is to 
be used. Where there is not sufficient camber, the treatment shown 
in Figure 23, B will be necessary in order to avoid the concave line 
shown in Figure 24, A. 
The superelevation is increased from the zero point (either at the 
vertex, as shown in Figure 23, A, or at the far end of the structure, 
as shown in Figure 23, B, to a maximum value at the end of the 
