Horizontal Alignment Considerations. It is best to avoid locating an intersection on
a curve. Since this is often impossible, it is recommended that intersection sites be
selected where the curve superelevation is 1⁄2 in/ft (22 mm/m) or less. It is also recommended
that intersections be located where the grade on the major roadway is 6 percent
or less, with 3 percent the desirable maximum. Intersection angles of 70° to 90°
are provided on new or relocated roadways. An angle of 60° may be satisfactory if
right-of-way is to be purchased for a future grade separation and the smaller angle will
avoid reconstruction of the intersecting road. In such cases, it may be desirable to
locate the intersection so the separation structure can be constructed in the future
without disrupting the intersection operation.
Relocation of the minor road is often required to meet the desired intersection
location, to avoid roadway segments with undesirable vertical alignments, and to
adjust intersection angles. Horizontal curves on the minor roads should be designed
to meet the design speed of the road. The minor road alignment should be as
straight as possible. Figure 2.31 shows the alignment for a typical rural crossroad
relocation.