Citation

Easa SM. Transp. Res. Rec. 1994; 1445: 1-11.

Copyright

(Copyright © 1994, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Existing sight distance models of highway horizontal (vertical) curves are applicable only to simple circular (parabolic) curves. These simple models may greatly overestimate the lateral clearance needs for reverse horizontal curves and the curve length requirements for reverse vertical curves. No available analytical model quantifies the effects of the alignment reversal on sight distance characteristics. The geometric and sight distance characteristics of reverse horizontal and vertical curves are presented. For reverse horizontal curves the available sight distance is related to the parameters of the two circular arcs, the length of the common tangent, the locations of the driver and object, and the location of the vision-limiting obstacle. The obstacle may be located within the circular arcs or the common tangent. For reverse vertical curves the available sight distance is related to the parameters of the crest and sag arcs, the length of the common tangent, the locations of the driver and object, and their heights. The sight-hidden zone (dip) that may exist on a reverse horizontal (vertical) curve is examined. The sight distance profiles and minimum sight distances of reverse and simple curves are compared.

Language: en

Keywords

Accident prevention; Mathematical models; Alignment; Curves (road); Highway systems; Geometry; Transportation personnel; Structural design