FIGURE 2.7 Intersection sight triangles. (a) Sight triangles. (b) Vertical components. a1 the distance,
along the minor road, from the decision point to 1⁄2 the lane width of the approaching vehicle on the major
road. a2 the distance, along the minor road, from the decision point to 11⁄2 the lane width of the approaching
vehicle on the major road. b intersection sight distance (ISD). d the distance from the edge of the traveled
way of the major road to the decision point; the distance should be a minimum of 14.4 ft (4.39 m) and 17.8 ft
(5.43 m) preferred. (From Location and Design Manual, Vol. 1, Roadway Design, Ohio Department of
Transportation, with permission)