The intersections created by the projection of a minor road from the tangent of a major road at a curve allow drivers to make an unusual form of left-turn movement and engender some operational patterns that may lead to difficulties in assigning right-of-way. These curved-tangential intersections appear to be more common on secondary or local rural roads, but they are not confined to those settings. Special design issues may arise at these skewed intersections at the beginning or end of the curve. Horizontal sight restrictions and middle ordinate values that would define an adequate line of sight through a curve are considered. At locations where curved roadways intersect with tangential roadways, using stopping sight distance alone to evaluate the adequacy of sight distance around the curve does not appear to be sufficient; a sight distance adequate for stopping may not satisfy intersection sight needs. Current intersection sight-distance design criteria may not fully address the operational behaviours found at these curved intersections. After relevant issues and special needs are considered, conceptual design criteria for intersections of curved roadways with projecting tangential roadways are developed. An example application of the method indicated that this intersection type needs a much larger roadside area clear of sight obstructions than that required solely by criteria for stopping sight distance. These intersections with projecting tangential roads at curves will require more attention when new projects are designed and when old roads are retrofitted.
Abstract