DESIGN REQUIREMENTS OF EQUAL-ARC UNSYMMETRICAL VERTICAL CURVES

Highway designers occasionally use unsymmetrical vertical curves in lo cations where the vertical clearance controls, In this case, the symme trical curve, which has a constant rate of change of grade, is replace d with two arcs, which have two different rates of change of grade and a common point of tangency. Traditional unsymmetrical curves are desi gned so that the point of common tangency (point of compound curve, PC C) is at the same station of the point of intersection between the cur ve's two tangents. However, a better unsymmetrical curve can be achiev ed by locating the PCC in the middle of the curve. The resulting curve , called the equal-arc unsymmetrical (EAU) curve, enhances sight dista nce, highway aesthetics, driver comfort, and vertical clearance. In th is paper, the sight distance profile on the EAU curve is analyzed and compared to that of the traditional curve. The EAU curve was found to improve the minimum available sight distance compared to the tradition al curve, and thus the required length of an EAU curve to satisfy a sp ecific sight distance would be shorter than that of a traditional curv e. Also, design length requirements for the EAU curve that satisfy sto pping (daytime and nighttime), passing, and decision sight distances a re developed.