Innovative Roadside Design Curve of Lateral Clearance: Roadway Spiraled Horizontal Curves

Abstract

This paper presents an innovative design method for determining lateral clearance needs on a spiraled horizontal curve to satisfy sight distance requirements. The roadside lateral clearance is represented by a spiraled horizontal curve that is easy to implement in practice. The design parameters were determined. The characteristics of the corresponding lateral offsets were explored for the influential roadway factors, including required sight distance or design speed, curve radius, curve length, spiral curve length, and station location expressed in fraction of sight distance. The results show that ratio of spiral curve length to required sight distance is the major factor that affects the ratio of the lateral offset to the maximum offset at a circular curve. A single design chart and a design table also are provided as alternative design tools to determine the offset for a specific obstruction location. The proposed design method not only greatly improves the AASHTO approximate approach, but also provides an alternative approach to improving design consistency on horizontal alignments. This paper complements another paper on lateral clearance needs for simple horizontal curves.