For safe and efficient highway operation, sight distance has been of great interest to researchers in the field of highway geometric design. Several formulas have been developed to relate the available sight distance to the horizontal and vertical alignment of the highway and the existing obstructions. Among these formulas is the one presented by (AASHTO) to determine the available sight distance on a simple horizontal curve with a length greater than the sight distance. For shorter curves in which the sight distance is greater than the curve length, other methods have been developed. However, none of these methods considered the case of continuous lateral obstructions or complicated horizontal alignments. Consequently, it has been recommended that the available sight distance be checked graphically or in the field. For this study, general analytical procedures were developed to check the available sight distance on horizontal alignments with single and continuous obstructions. A horizontal alignment may consist of any combination of horizontal components, such as straight segments, circular curves, and spiral curves. Based on the analytical procedure, a computer software program was developed to establish the no-passing zones on two-lane highways, according to the specifications used by the Ministry of Transportation of Ontario, Canada. The developed procedures and computer software proved to be very accurate. Using them would save time and effort and would avoid possible human errors when the sight distance is checked using current graphical or field techniques. The computer software can also be used to develop design tables and charts for the available sight distance on different horizontal alignments.

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Journal Transportation Research Record
Hassan, Y, Easa, Said M. (Said M.), & Halim, A.O. (1995). Sight distance on horizontal alignments with continuous lateral obstructions. Transportation Research Record, (1500), 31–42.