Sight Distance at Undercrossings

Daylight sight distances on highway vertical curves in sag may be limited by a structure crossing the right of way. Conventional formulas for the determination of this sight distance are based on the special case in which the critical edge of the structure is directly above the vertex of the vertical curve. Despite this limitation, these equations are considered to be applicable regardless of the position of the critical edge with respect to the vertex of the vertical curve. Specific formulas are derived which are correct for any position of the structure; the results obtained by use of the conventional equations are compared with those using the specific formulas.