Design Consistency of Horizontal Alignments on Two - Lane Trunk Roads
No Thumbnail Available
Date
2007-02
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Design consistency is the conformance of highway’s geometric and
operational features with driver’s expectancy. A technique to evaluate the
consistency of a design is to evaluate changes in operating speeds along an
alignment. To use operating speed as a consistency tool requires the ability
to accurately predict speeds as a function of the roadway geometry. The
current Ethiopian Roads Authority geometric design manual is based on the
design speed concept. However, due to the constraints resulting from
roadway elements, right-of-way, and environmental features, consistency in
operating speed cannot be guaranteed. In order to make informed decisions
to ensure highway geometric design consistency, the consistency of
geometric design of operating speed on simple curve and tangent section was
studied. Forty three sections for both of horizontal curve sections and
tangent sections were selected, within easy reach of Addis Ababa. Roadway
geometric design variables were obtained from design documents and
through field measurements. The speeds of passenger cars, buses, and
trucks were measured on each curve and its approaching tangent, under dry
day time condition. This study was focused on two major issues, in
evaluating the geometric design consistency of the selected alignments and
in developing operating speed predicting models for the selected sections.
Therefore, the results obtained from consistency evaluation shows that four
sections between simple curves and tangents were in poor conditions.
Whereas, consistency evaluation between design speed and operating speed
shows that thirty seven sections in horizontal curves and thirty four sections
in tangents sections was in a poor conditions. Two models were found for
horizontal curves and tangents. Model found for the horizontal curves were
governed by the combination of grade and superelevation. Furthermore
model for tangent section were governed by grade.
Description
Keywords
Trunk Roads