ABSTRACT
The Ghana Highway Authority Road Design Guide (GHA RDG) is
over two decades old since it was published as a draft document in 1991. It was
expected to be periodically updated and revised based on observations,
comments, suggestions and criticisms from stakeholders as they utilised it. As
of October 2015 however, no update or revision has been carried out.
Increasingly, designers undertaking projects for the Ministry of Roads and
Highways, in-house design engineers in the Ghana Highway Authority, consultants
and other expatriate designers of projects in Ghana are resorting to the use of
several other manuals as references for highway designs. As a result of this
highway design in Ghana has become more laborious; it is difficult to ensure
uniformity of design, consistency of designs across the trunk road network and
also vetting of consultants’ design presentations has become very laborious.
The aim of this study was to make an appraisal with a view to modifying the
Guide. The specific objectives of this study were first to critically assess
the suitability of the GHA RDG and its contents regarding capacity, safety and
economy for the geometric design of elements for modern trunk and urban roads.
Secondly, the study was also to make an assessment of commonly used sources and
standards for road element design in Ghana over the last ten years and thirdly
to provide a theoretical basis for inclusion or otherwise in the GHA RDG. In
order to achieve the objectives of the study views of experienced highway
designers regarding the suitability of the GHA RDG for current highway design
were sought through the administration of questionnaire. The GHA RDG was also
compared with some current highway design manuals in Africa and the United
States of America for suitability. The results indicate that the GHA RDG does
not meet several of the requirements for current highway design in Ghana.
Because of its deficiencies, highway designers in Ghana are resorting to other
standards including the Green Book, AASHTO’s A Policy on Geometric Design of
Highways and Streets, and the Ugandan Geometric Design Manual, to mention a
few, as references for geometric design. It is therefore necessary to revise
several aspects of the Guide to ensure its suitability for modern highway
designs in Ghana. Also, many areas would require revision and the inclusion of
several topics which are not covered. A recommended table of contents for a
revised GHA Road Design Guide has been proposed.
CHAPTER 1: INTRODUCTION
1.1 Background
The
use of highway design standards, often presented as highway design guides or
manuals, is to fulfil a number of objectives, key amongst which are:
1. To ensure minimum levels of safety and
comfort of road users
2.
To arrive at an economic design
3.
To maintain uniformity in
alignments, drainage and other road facilities
4.
To ensure sufficient capacity of
road sections, intersections and other road related
facilities
in order to cater for design traffic demand
In 1991 the Ghana Highway
Authority (GHA), drawing from unwritten Ghanaian standards and some standards
or guidelines for design in use in countries like Japan, Britain, USA and Malawi
amongst others, put together a draft Road Design Guide (RDG) to be primarily
used by road designers in GHA and also some local and foreign consultants. This
was a period when most designs were carried out in-house. It was intended to
also serve the needs of the Department of Feeder Roads and the Department of
Urban Roads. The Road Design Guide was a draft document expected to be
periodically updated and revised based on practice, observations, comments,
suggestions and criticisms from all stakeholders (GHA, 1991). As at October
2015 however no update or revision had been carried out. Over two decades after
its publication vehicle standards have improved, concepts for safe design
roadways have seen tremendous improvement. Also, the use of computers has
dramatically changed how designs are carried out and also the level of accuracy
that can be achieved.
1.2 Problem
Statement
In Ghana an urban area is
defined as any settlement inhabited by 5,000 or more persons. Between the years
1948 and 2000 the number of urban areas has increased from 41 to 364 (UNEP et
al., 2012). The vehicle population in 2005 was 767,067 and this increased to
1,127,986 in
2009 resulting in an annual average growth rate of 8.3% during that period (MRH
et al., 2011).
In recent times, elevated highways, grade-separated
intersections, multi-modal intersection designs, forgiving road environment and
smoother alignments are being employed more for better traffic management and
safety. This has resulted in the implementation of infrastructure projects such
as the Tetteh Quarshie interchange (Accra), the George Walker Bush Highway
(Accra), the Achimota – Ofankor multi-lane ‘segregated’ with varied access
controls highway (Accra), the Sofoline Interchange (Kumasi), the Asokwa
Interchange (Kumasi), the Nkawkaw by-pass, the Nsawam by-pass, and Suhum
Interchange, to mention a few. There is therefore an increased need for designs
to handle higher levels of traffic and traffic conflicts with a view to safety
and economy. In other words there is the need to design roads which allow for
greater mobility and speed without endangering the safety of pedestrians and
other road users.
The GHA Road Design Guide
provides some level of uniformity of design where designs fall within its
scope. However, it is deficient in solutions such as roundabouts,
grade-separated intersections and certain other aspects of geometric design
like ‘broken-back’ alignment situations and number of curves per kilometre.
These and others are reasons necessitating its revision.
Increasingly, in-house GHA
highway geometric designers, and consultants undertaking designs for the
Ministry of Roads and Highways are resorting to the use of several other
manuals as references for highway designs in Ghana, and as a result:
i)
Highway design in the Ghana has
become more laborious for the designer
ii)
It is difficult to ensure uniformity
of design across the trunk road network
iii)
Vetting of consultants’ designs has become very
laborious for road agency staff
It is not even clear which manuals are most frequently
utilised and for what purposes or elements of design. Should the GHA RDG be
revised? What additional content might be necessary to be included and for what
purposes or design elements? This study sought to find answers
to some of these searching questions by engaging stakeholders and undertaking a
review of literature.
1.3 Study
Justification
The results of the
study would achieve the following:
i)
Establish the strengths and deficiencies
in the GHA Road Design Guide (1991).
ii)
Improve upon the understanding of
what manuals and guidelines are being used for designs in Ghana.
iii)
Recommend modifications to be
considered in the revision of the GHA Road Design Guide (1991).
1.4 Study
Objectives
The objectives of
the study were:
i)
Assess the suitability or otherwise
of the GHA Road Design Guide (1991) for the geometric design of elements for
modern trunk and urban roads.
ii)
Make an assessment of commonly used
sources and standards for road element design in the last ten years and provide
a basis for inclusion or otherwise in the
GHA
RDG.
iii)
Propose a detailed Table of Contents
for a revised Manual, highlighting the main elements and requirements.
1.5 Scope
of Study
The
focus of the research was the geometric design of trunk and urban roads. The
study therefore covered the following:
i)
Theoretical assessment of geometric
design criteria, controls and elements in the GHA Road Design Guide.
ii)
Comparison between GHA Road Design
Guide and other geometric design manuals.
1.6 Study
Limitation
The study was conducted within
a relatively short period of time. Consultations with stakeholders, based on
which analysis was done, was therefore conducted within limited time. Views and
comments of a broad spectrum of stakeholders could therefore not be solicited.
Hence although the findings, conclusions and recommendations of this study are
a result of thorough analysis they may not be exhaustive.
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