Discussion of 'Optimal Vertical Alignment Analysis for Highway Design' by T. F. Fwa, W. T. Chan, and Y. P. Sim

摘要

The optimization algorithm presented by the authors to design vertical alignment is correct, although based on an erroneous requirement. Nonoverlapping of horizontal and vertical curves is precisely not a common constraint in the vertical alignment design of roads. Highways have always been designed as separate 2D horizontal and vertical alignments, and certain criteria have been recommended within general guidelines to enhance the coordination of horizontal and vertical alignments. Excellence in the design of their combination increases usefulness and safety, encourages uniform speed, and improves appearance, nearly always without additional cost (AASHTO 2001).