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8/17/2019 QHDM Vol1 Part02 Planning OctFinal
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Volume 1
Part 2Planning
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VOLUME
1
PART
2
PLANNING
VOLUME
1
Disclaimer
The
State
of
Qatar
Ministry
of
Transport
(MOT)
provides
access
to
the
Qatar
Highway
Design
Manual
(QHDM)
and
Qatar
Traffic
Control
Manual
(QTCM)
on
the
web
and
as
hard
copies
as
Version
(1.0)
of
these
manuals,
without
any
minimum
liability
to
MOT.
Under
no
circumstances
does
MOT
warrant
or
certify
the
information
to
be
free
of
errors
or
deficiencies
of
any
kind.
The
use
of
these
manuals
for
any
work
does
not
relieve
the
user
from
exercising
due
diligence
and
sound
engineering
practice,
nor
does
it
entitle
the
user
to
claim
or
receive
any
kind
of
compensation for damages or loss that might be attributed to such use.
Any future changes and amendments will be made available on the MOT web site. Users of these
manuals
should
check
that
they
have
the
most
current
version.
Note:
New
findings,
technologies,
and
topics
related
to
transportation
planning,
design,
operation,
and
maintenance
will
be
used
by
MOT
to
update
the
manuals.
Users
are
encouraged
to
provide
feedback through the MOT website within a year of publishing the manuals, which will be
reviewed, assessed, and possibly included in the next version.
Copyright © 2015. All rights reserved.
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ويه
ة ار
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ز
‐ Qatar Highway Design Manualدو ط ر د اطق و ط)ات و QHDMدو (
) ير
و
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Qatar Traffic Control Manual ‐ QTCMر
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Contents Page
Acronyms and Abbreviations .................................................................................................... vii
1 Highway Strategy .............................................................................................................. 1
1.1 Introduction .................................................................................................................... 1
1.2 Vision, Goals, and Objectives.......................................................................................... 1
1.3 Project Types and Scope ................................................................................................. 3
1.4 Transportation Planning Process in Qatar ...................................................................... 4
1.5 Land Use Considerations ................................................................................................ 5
1.5.1 Land Acquisition .............................................................................................. 5
1.6 Appraisal ......................................................................................................................... 7
2 Projects Involving New Roads ........................................................................................... 9
2.1 Planning and Design Objectives: Provide Mobility and Accessibility ............................. 92.2 Planning Development Access for New Roads ............................................................... 9
2.3 Project Development Process......................................................................................... 9
2.3.1 Development Process for New Road Projects ............................................... 10
2.3.2 Project Development Process: Design and Build (D&B) ................................ 12
3 Project Development Process for Interchange Design Studies (Existing Reconstruction or
New) ............................................................................................................................... 15
3.1 Step 1: Establish Data Collection Requirements and Obtain Data ............................... 15
3.1.1 Develop Interchange Planning and Design Framework ................................ 16
3.1.2 Stakeholder Involvement .............................................................................. 16
3.1.3 Develop Project Planning and Design Criteria ............................................... 17
3.2 Step 2: Confirm Study Approach, Evaluation Criteria, and Decision Process ............... 17
3.2.1 Determine Evaluation Criteria and Technical Approach ............................... 17
3.2.2 Develop Design Year Traffic and Select Most Likely Alternatives ................. 18
3.3 Step 3: Conduct Interchange Type Studies ................................................................... 18
3.3.1 Concept Engineering Design.......................................................................... 18
3.3.2 Stakeholder Review and Screening ............................................................... 19
3.4 Step 4: Functional Geometric Design of Screened Alternatives ................................... 19
3.5 Step 5: Select Preferred Alternative, Document and Develop Final Engineering
Plans .............................................................................................................................. 20
4 Projects Involving Existing Roads .................................................................................... 21
4.1 Unique Characteristics of Projects Involving Existing Roads ........................................ 22
4.2 Design of Reconstruction Projects ................................................................................ 22
4.2.1 Relationship of Safety Performance to Design Elements .............................. 23
4.2.2 Risk Management Guidelines ........................................................................ 25
4.2.3 Reconstruction Design Approach .................................................................. 26
4.3 Designation of Eligibility for 3R Treatment .................................................................. 27
4.4 Design of 3R Projects .................................................................................................... 28
4.4.1 Context Sensitive Safety Enhancements for 3R Projects .............................. 29
4.4.2 3R Safety Enhancements for Rural Highways ............................................... 294.4.3 3R Safety Enhancements for Urban Roads ................................................... 32
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5 Functional Classification as a Primary Design Control...................................................... 33
5.1 Qatar Road Classification ............................................................................................. 33
5.2 Definition of Urban and Rural Roads ........................................................................... 34
5.3 Functional Classification in Urban Areas ..................................................................... 345.3.1 Expressways .................................................................................................. 34
5.3.2 Arterials ........................................................................................................ 35
5.3.3 Collector-Distributor Roads .......................................................................... 36
5.3.4 Collector Roads ............................................................................................. 36
5.3.5 Local .............................................................................................................. 38
5.4 Functional Classification in Rural Areas ....................................................................... 38
5.5 Special Corridors .......................................................................................................... 39
5.6 Temporary Roads ......................................................................................................... 40
5.7 Application of Functional Classification in Design ....................................................... 40
5.7.1 Key Parameters ............................................................................................. 405.7.2 Network Connections ................................................................................... 46
5.7.3 Transport Provisions for Non-car Users ....................................................... 50
6 Design Vehicles............................................................................................................... 53
6.1 Introduction ................................................................................................................. 53
6.2 Vehicle Weights and Dimensions ................................................................................. 53
6.2.1 Abnormal Loads and High Load Routes ........................................................ 53
6.3 Typical Design Vehicles ................................................................................................ 54
6.3.1 Definitions and Principles ............................................................................. 54
6.3.2 Design Vehicles ............................................................................................. 54
6.3.3 Swept Path Analysis ...................................................................................... 55
7 Driver Performance and Human Factors ......................................................................... 59
7.1 Introduction ................................................................................................................. 59
7.2 Qatar Driver Characteristics ......................................................................................... 59
7.3 The Task of Driving ....................................................................................................... 60
7.4 Vehicle Guidance ......................................................................................................... 61
7.4.1 Road Following ............................................................................................. 61
7.4.2 Car Following ................................................................................................ 61
7.4.3 Passing Maneuvers ....................................................................................... 61
7.4.4 Gap Acceptance, Merging, and Other Guidance Activities .......................... 617.5 Information System ..................................................................................................... 61
7.5.1 Traffic Control Devices ................................................................................. 61
7.5.2 Road Environment ........................................................................................ 62
7.6 Information Handling ................................................................................................... 62
7.6.1 Reaction Time ............................................................................................... 62
7.6.2 Primacy ......................................................................................................... 62
7.6.3 Expectancy .................................................................................................... 62
7.7 Driver Error .................................................................................................................. 63
7.8 Speed and Design ......................................................................................................... 64
7.9 Design Assessment ...................................................................................................... 66
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8 Traffic Characteristics...................................................................................................... 67
8.1 Introduction .................................................................................................................. 67
8.2 Traffic Volume .............................................................................................................. 67
8.2.1 Annual Average Daily Traffic ......................................................................... 678.2.2 Design Hour Traffic ........................................................................................ 67
8.3 Highway Capacity Concepts .......................................................................................... 69
8.3.1 Capacity Definition ....................................................................................... 69
8.3.2 General Characteristics and Application ....................................................... 70
8.3.3 Level of Service .............................................................................................. 71
8.3.4 Traffic Operations Analysis ............................................................................ 72
8.3.5 Level of Service as a Design Control .............................................................. 72
8.3.6 Influence of Design Features on Capacity ..................................................... 73
9 Access Control and Access Management ......................................................................... 75 9.1 General Conditions ....................................................................................................... 75
9.2 Access Management ..................................................................................................... 76
9.2.1 Basic Principles of Access Management ....................................................... 76
9.2.2 Access Classifications .................................................................................... 77
9.2.3 Methods of Controlling Access ................................................................... 77
9.2.4 Access Management and Safety Performance ............................................. 78
10 Speed and Design ........................................................................................................... 79
10.1 Introduction .................................................................................................................. 79
10.2 Operating Speed ........................................................................................................... 79
10.3 Speed Variations ........................................................................................................... 79
10.4 Design Speed ................................................................................................................ 80
10.5 Posted Speed ................................................................................................................ 80
11 Facilities for Pedestrians ................................................................................................. 81
11.1 General Considerations ................................................................................................ 81
11.2 Designing for Pedestrians ............................................................................................. 81
11.3 Pedestrian Capacity and Pedestrian Facilities .............................................................. 81
12 Facilities for Cyclists ........................................................................................................ 85
13 Parking ........................................................................................................................... 87
References ............................................................................................................................... 89
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Tables
Table 3.1 Typical Stakeholders and Their Issues for Interchange Projects ....................... 16
Table 4.1 Relative Relationship of Geometric Design Features to Crash Frequency or
Severity by Type of Road ................................................................................... 24
Table 5.1 Key Characteristics of Urban Roads ................................................................... 41
Table 5.2 Key Characteristics of Rural Roads .................................................................... 43
Table 5.3 Network Connections for Urban Roads ............................................................. 47
Table 5.4 Network Connections for Rural Roads .............................................................. 48
Table 5.5 Transport Provisions for Multimodal Users on Urban Roads ............................ 51
Table 5.6 Transport Provision for Non-car Users on Rural Roads ..................................... 52
Table 6.1 Maximum Vehicle Weights and Dimensions ..................................................... 53
Table 6.2 Typical Design Vehicles ...................................................................................... 55
Table 8.1 General Definitions of Levels of Service (Uninterrupted Flow) ......................... 71
Table 8.2 Level of Service and Volume to Capacity (v/c) .................................................. 73
Table 8.3 Average Control Delay Criteria for Signalized Intersection Levels of Service.... 73
Table 9.1 Potential Crash Effects of Reducing Access Point Density ................................ 78
Table 10.1 Relation Between Design and Posted Speeds ................................................... 80
Table 11.1 Level of Service, Pedestrian Area and Flow Rates ............................................. 82
Figures
Figure 3.1 Example Single-line Concept Plan View over Aerial .......................................... 19
Figure 4.1 Conceptual Relationship between Available Sight Distance and Safety at Crest
Vertical Curves ................................................................................................... 25
Figure 4.2 Safety Edge ........................................................................................................ 29
Figure 4.3 Paved Shoulder and Rumble Strip Example ...................................................... 30
Figure 4.4 Horizontal Curve Treatments ............................................................................ 31
Figure 5.1 Urban Road Network ......................................................................................... 34
Figure 5.2 Expressway with CD Roads ................................................................................ 35
Figure 5.3 Arterial ............................................................................................................... 36
Figure 5.4 Collector Road ................................................................................................... 37
Figure 5.5 Local Road .......................................................................................................... 38
Figure 5.6 Rural Road Network .......................................................................................... 39
Figure 5.7 Illustration of a Road’s Mobility Versus Access Functions ................................ 45
Figure 5.8 Freeway to Freeway Connection ....................................................................... 49
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Figure 5.9 Expressway to Urban Arterial Connection ........................................................ 49
Figure 5.10 Rural Freeway to Rural Arterial Connection...................................................... 50
Figure 6.1 Swept Path Parameters for Typical Tractor-Semitrailer Combination .............. 57Figure 7.1 Crash Types and Indicative Fatality Risks at Various Speeds ............................ 65
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Acronyms and Abbreviations
AADT annual average daily traffic
AASHTO American Association of State Highway and Transportation Officials
ADT average daily traffic
D&B design and build
DHV design hour volume
HCM Highway Capacity Manual (2010)
HSM Highway Safety Manual (2010)
HV hourly volume
ITS intelligent transportation system
km kilometer
kph kilometers per hour
LARISA Land Acquisition and Roadway Improvement Strategic Approach
LOS level of service
m meter
MMUP Ministry of Municipality and Urban Planning
PPD Public Parks Department
QHDM Qatar Highway Design Manual
QNRSS Qatar National Road Safety Strategy
s second
3R Resurfacing, Restoration, and Rehabilitation
TMPQ Transportation Master Plan for Qatar
v/c volume to capacity
vpd vehicles per day
vph vehicles per hour
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1 Highway Strategy
1.1 IntroductionPlanning for new cities or for transportation projects requires close cooperation among
town planners, transport planning specialists, and highway engineers. Transportation
infrastructure serves as the lifeline for the movement of people and goods, and is
therefore an essential component of good national and town planning practice.
Transportation infrastructure requires time and resources to construct, but if
effectively managed, it can promote economic growth and the well-being of Qatar’spopulation. Before construction of any transportation infrastructure, transport
specialists and town planners should confirm that the facilities will aid the vision and
goals of Qatar’s growth while adhering to the current and future expansion policies.
Transportation infrastructure is intended for use by the public, who will have an
interest in the type of infrastructure provided, its features and characteristics, and the
timing and schedule of its implementation. The public includes road users, adjacent
property owners, businesses and local residents, all of whom will have different
interests and concerns about the project. It is important to identify and involve all such
stakeholders during the planning stage. This will allow interested parties to express
their views and concerns, and thus to benefit the users of transportation facilities.
This section states the vision and objectives of Qatar’s transport strategy, (based on the
latest Transportation Master Plan for Qatar (TMPQ), Transport Objectives for Qatar) and
provides planners and engineers with guidelines to enable the appropriate planning of
infrastructure projects. In line with the intent of the Qatar Highway Design Manual
(QHDM), it promotes the design and construction of highway infrastructure in Qatar to a
high and common standard, which is a basic component of good planning practice.
1.2 Vision, Goals, and ObjectivesQatar’s Transport Strategy vision is to “Promote safe, efficient and environmentally
sustainable transport for people and goods, responding to individuals’ needs for
mobility and supporting economic growth.”
The transportation goals for Qatar are categorized into five areas:
1. Quality of life and community
2. Economy
3. Mobility
4. Environment
5. Finance and governance
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Goals for each area are translated into objectives and described as follows.
Quality of Life and Community
• Provide an attractive and integrated multi-modal transport system to accomplishthe following:
− Serve the anticipated increase in population.
− Provide adequate mobility options for people of all social sectors.
− Increase transport network access for remote and disadvantaged zones and
communities.
• Implement a transport system with minimum adverse effects on quality of life, such
as air pollution, noise emission, or barrier effect of infrastructure.
• Integrate land use and transport planning.
• Respect cultural heritage in alignment and design of transport facilities.
• Improve safety by reducing the number and severity of crashes.
Economy
• A smart integrated transport system and an appropriate infrastructure is vital to
accomplishing the following:
− Support the existing and future massive economic and industrial growth.
− Implement an efficient movement of goods, services, and passengers.
• Provide attractive and equivalent access to education sites by all modes of
transport.
Mobility
• Identify corridors for large-scale transport of passengers and goods.
• Use an integrated transport system to respond to all travel demands.
• Employ phased development of transport networks for all modes as the long-range
forecast transport demand evolves.
• Provide an effective traffic management system to eliminate current congestion
and delays and help avoid over-saturation in the future.
• Improve safety (and security) of Qatar’s road transport system as part of the QatarNational Road Safety Strategy (QNRSS)
• Achieve high transport awareness and education.
• Move away from only meeting demand by provision of additional infrastructure
and start with managing demand more effectively.
• Balance transport modes and minimize conflicts between them.
• Improve efficiency and reliability of traffic conditions for motorist and public
transport users by better information systems.
•
Provide accessibility to all highway and transport users.
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Environment
• Consider principles of sustainability when developing Qatar’s integrated transport
system, now and in the future, particularly an integration of transport development
with land use development.
• Reduce or minimize energy consumption in transport.
• Increase awareness of decisions makers and planners about environmental impacts
of different transport modes.
• Raise awareness with general transport users about the impacts of their mobility
behavior on the natural, manmade, and social environments.
• Provide more sustainable options for mobility of Qatar’s residents, such as
improved public transport services and more attractive bike and pedestrian
facilities.
• Change transport behavior of residents and visitors to more sustainable modes,
adequate trip lengths, or other preferred options.
Finance and Governance
• Minimize the adverse economic impacts of the car; that is, minimize the costs
resulting from today’s car-dominated transport system on environment, health,
and social life.
• Achieve a reasonable cost-benefit ratio of investments in the transport system.
1.3 Project Types and ScopeThere are three basic types of projects that involve highway and transportation
infrastructure:
• New roads
• Reconstruction of existing roads
• Rehabilitation, restoration, or resurfacing of existing roads (3R)
New roads may include service roads, minor arterials, or major arterials, any of which
may involve new intersections with the existing road network. Reconstruction may
include improvements to existing roads, such as addition of motor vehicle capacity,addition or enhancement of facilities for nonmotorized users, or a combination of
these. 3R projects are those for which the basic roadway remains, but major repairs to
the pavement, bridges, or other infrastructure are necessary. Both reconstruction and
3R projects typically will include replacement or major repair of highway infrastructure
that has reached the end of its service life or has been damaged by an external event.
Reconstruction projects may include capacity or other similar improvements.
All project types require preplanning, but because they all differ in scope and purpose,
some require greater planning and scrutiny.
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Road and highway projects that require planning approvals include:
• Highway widening
• Access to new developments• Intersection improvements
• Proposed new pedestrian and bicycle facilities
• New service roads, local roads, and arterials in a new, mixed development, for
example, retail, commercial, residential, and recreational
1.4 Transportation Planning Process in QatarQatar is undergoing tremendous economic and industrial growth. That growth has
resulted in a rapid population increase and the urgent need to develop infrastructure
projects and major transport projects. The economic and industrial growth are linked
to the National Vision that aims at transforming Qatar into an advanced country by
2030, capable of sustaining its own development and providing for a high standard of
living for all of its people for generations to come.
The transport strategy developed from the transport master plan provides direction for
the planning authority for a systematic approach in the implementation of transport
infrastructure on the road network. It also calls for the development of an adequate,
modern, and innovative public transport system to accommodate the future transport
needs of Qatar.
The transportation planning process identifies parts of the transport network wherenew investments in transport infrastructure or redesign of existing facilities would be
beneficial. Proposals are usually developed within the context of master plans.
The Overseeing Organization’s focus is to deliver transport infrastructure in ways that
promote sustainable travel and safeguard the efficient and safe functioning of the
transport system.
A typical planning process considered by the Overseeing Organization for a transport
infrastructure project proposed by a developer will involve the following:
• Receipt of developer’s application.
• Initial review of the project carried out to make sure that local communities are not
adversely affected by development. This could involve a preapplication meeting
with the developer to discuss the project details.
• Submitting of a formal application by the developer to the Overseeing Organization
with the supporting information.
• Meeting with the developer and agreeing upon the terms of reference and the
scope of work for the project.
• Examination of the project by the Overseeing Organization, which then will advise
the developer to undertake a transport or traffic impact study for the project.
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• Obtaining formal comments from the Overseeing Organizations regarding the
project and the transport report.
• Assessing the proposed land use and the impact of the development on its
surroundings by considering the impact on transport and the highway network. For
the planning process, consideration will be given to such, but limited to factors as
road classification, level of service (LOS), highway design, increased traffic and
congestion that may harm the economy, and increased crashes.
• Reviewing the transport report and, for the final planning approval, achieving
developer agreement with the appropriate highway infrastructure design.
• There is an appeal period and process if an application is refused on technical
grounds. Further information regarding different types of appeals should be
addressed to the Overseeing Organization. Scheduling highway planning
conditions—that is, agreeing upon a time scale in which to implement—will be the
responsibility of the Overseeing Organization for highway and traffic works.
1.5 Land Use ConsiderationsThe designer needs to be aware of land ownership issues when developing highway
plans. The variety of land uses and landowners in Qatar can make the acquisition of
land for road infrastructure difficult, costly, or not in the interest of the public. In
particular, the acquisition of areas of special-category lands, such as burial grounds and
military facilities, will involve additional procedures and may require replacement land
to be provided.
It is thus important that, in preparing feasibility studies and concept designs, the
designer becomes familiar with the land ownership and associated issues near the
proposed program of work.
Land uses surrounding a road corridor fundamentally affect the design choices for road
projects and similarly affect the expected impact of implementation of such a project.
Consequently, traffic impact studies covering all modes of transport are required for
new developments in order to assess the following:
• The overall transport and environment implications• The impact of additional traffic on the adjoining highway network
• The internal/external site access arrangements
• Any need for mitigation measures in support of new development
1.5.1 Land Acquisition
As a general practice, the designer should attempt to maintain the existing right-of-way
corridor when planning for road improvement and design solutions. If design solutions
cannot be arrived within the existing right-of-way corridor, then additional land may be
required. In such instance, the acquisition of adjacent properties may assist in
achieving, geometric improvement solutions for roads and the surrounding links,
interchanges and intersections, in order to provide a continuation of proposed design
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solutions. Land acquisition may also assist in meeting project goals of an improved
vehicular and pedestrian circulation network and meet future demands where poor
and acceptable conditions are identified.
A Land Acquisition and Roadway Improvement Strategic Approach (LARISA) can be
developed to indicate sides of roads where land acquisition should be concentrated
and to minimize the impact of road corridors to one side versus both sides. This
approach will efficiently lead the design process in road improvements and design
solutions.
LARISA is based on the site survey, existing land and building assessments, and
identifying project constraints and recommendations.
1. Existing Land and Building Survey
The principles of the site survey are subjective in nature and relative to surrounding
land uses, building conditions, and heights in comparison to adjacent properties,
incompatibility, heritage, or cultural landmarks. The site survey may identify the
following features, and others:
• Towers, residential and commercial
• Single and multi-family residential
• Heritage sites
• Rail and metro stations
• Vacant land
2. Existing Land and Building Assessment
The building survey shall seek opportunities for parcel acquisition of and vacant lands
and demolishing buildings that are old or in poor condition. A strategic approach was
formulated to identify the methods of land acquisition and demolition of structures
within the corridors. The demolition of adjacent properties should provide sufficient
room for widening and realigning the road. On the other hand, various constraints may
limit land acquisition and indicate structures to be avoided. The following are criteria
to be considered during the assessment:
• Likely to be avoided:
− Native single-family properties, which should have precedence over the leased
residential and commercial sites as constrained properties
− Buildings that cannot be acquired because of cultural, historical, religious, or
economic restrictions
− Multi-family residential buildings that preserve the character of the residential
area
− Buildings in good condition, developments under construction, or new
commercial buildings
− Sites or buildings that have architectural character suitable for the area
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− Shopping malls and large business areas
− Parks and recreational areas.
− Small strips or sections of land impact on rows of buildings
• Likely to be acquired:
− Substandard buildings, which are old or in poor condition, and large vacant
land, which are prime candidates for acquisition to accommodate road
improvements.
− Buildings where land use or occupation compatibilities conflict with
surrounding uses and are not applicable to the land use plan
− Land acquisition on one side of the road only to avoid or minimize impacts to
the opposite side
− Optimal use of buffer zones to avoid land takes on private properties,
especially with buildings
3. Constraints and Recommendations:
The field investigations shall yield specific recommendations for important buildings,
significant sites, and strategic existing utilities, which are categorized as constraints.
Land acquisition and removal of various stretches of roads confined to one side shall
be considered as part of value engineering approach during strategic planning stage.
Constraint plans should be developed in the early stages of the project. Restricted
buildings and sites should be avoided if possible in determining final roadway alignmentoptions or be used as an analysis tool for option development.
Considerable roadway improvements are needed not only to enhance vehicular and
pedestrian corridors but also to provide the minimum required space needed to make
roadway improvements.
The latest versions of the Ministry of Municipality and Urban Planning (MMUP)
documents, Guidelines and Procedures for Transport Studies and Land Acquisition
Process, outline procedures to be followed for assessing the transport impact of new
developments and the MMUP land acquisition process in Qatar.
1.6 AppraisalAs part of the planning process, the highway project appraisal reflects the need for
balanced improvement across the network. An appraisal is the method of assessing
whether investing financially in construction of a highway provides value to the
highway and transport users.
The planning process identifies parts of the transport network where investments in
new transport infrastructure or redesign of existing facilities would be beneficial.
Proposals are usually developed within the context of development plans. The purpose
of the appraisal is to compare the advantages and disadvantages of various transport
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infrastructure improvement proposals. Proposals are prioritized based on the costs and
benefits arising from traffic, economic, environmental, social, and safety effects on the
community, both in the short and long term.
The following are the key steps involved in carrying out an appraisal:
1. Define objectives and constraints.
2. Identify problems.
3. Identify solutions and designs. Develop policies or solutions to meet the objectives
and solve problems.
4. Perform measurement and forecasting. Forecasting the outcome for alternative
plans or scenarios over the life of the project using performance indicators.
Indicators should be operational (e.g., travel time), environmental (e.g., emissionsand social benefits), or economical (e.g., cost and benefit to the community during
the life of the project). Benefits are usually referred to as net present benefits,
which are the total project benefits minus costs of construction, maintenance, land
acquisition, and other costs.
5. Evaluate the process of applying weights to the indicators identified in step 4.
Weighting should reflect the Overseeing Organization’s policies, with input from
stakeholders.
6. Select a best-value solution. The highest total benefit that may be approved for
design completion and construction as appropriate.
The three levels of appraisal hierarchy are as follows:
1. Strategic: The focus is on developing broad options for consideration. Several
alternative strategic plans should be considered. For example, if a new town is
being built to provide residential housing, it is at this stage that the planner should
consider the orientation and the layout of the town’s road network.
2. Packages: A package is an alternative means of dealing with particular identified
problems. The package approach requires the planner to do the following:
− Consider the nature of problems and objectives for a particular area.
− Relate proposed solutions to the defined problems and objectives− Consider the impact the solutions have on the area as a whole.
3. Alternative: Alternative designs should be conceived within the context of defined
objectives and objectively identified and described transportation problems.
Sound appraisals require sound and defensible traffic forecasts. In making these
choices, reference should be made to the latest version of MMUP’s Guidelines and
Procedures for Traffic Studies.
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2 Projects Involving New Roads
2.1 Planning and Design Objectives: Provide Mobilityand AccessibilityA new road will have one of two basic purposes: to enable new development by making
the land accessible to the transportation road network, or to enhance the ability to
travel between two areas or destinations by providing an alternative route to an
existing route.
The planning of new roads to serve new development zones should take into account
the proposed land uses of the new development. The amount of road capacity and the
types and volume of travel, including pedestrian and cyclist, will be a function of the
type and density of the development. New road planning and design entails
development of a suitable road hierarchy classification that can be assigned to roads
serving both existing and new land uses. A key objective is the designation and ultimate
acquisition of right-of-way width.
2.2 Planning Development Access for New RoadsThis section provides planning and design considerations for planning access to
development by new roads and other transport infrastructure in Qatar to be approved
by Overseeing Organization for planning and eventually adopted by the Overseeing
Organization for road works. It includes guidance on the information required to satisfy
the transport and highway aspects of planning applications with particular regard to
safety, pedestrians, cyclists, public transport, service and private vehicles, and parking
standards.
2.3 Project Development ProcessRoad projects are undertaken to address specific transportation problems, such assafety, capacity, physical features, or accessibility. Generally, road problems fall into
three categories:
• Safety: There is a frequency and pattern of crashes well in excess of what should
be expected for the location, with such crash experience potentially treatable by
proven effective countermeasures.
• Demand exceeds capacity: Existing facilities do not meet current or projected
traffic demand as measured by the desired level of service for the facility.
• New development: Access needs to be provided to new developments.
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These types of problems may be observed for potential road users, be they motorists,
pedestrians, and cyclists. The problems that a project is intended to address should be
clearly defined and agreed upon by all stakeholders early in the project development
process. Therefore, it is important to actively involve stakeholders and seek their inputearly in the project. See also Chapter 1, of Part 20, Context Sensitive Design and
Solutions,
2.3.1 Development Process for New Road Projects
Once a project is planned and recommended for implementation, it goes through the
following major design phases with specific milestones before implementation:
scoping, concept design, preliminary design, detailed design, and tenders.
Construction, operation, and maintenance phases of projects are discussed in other
manuals. An exception to this process is design and build (D&B) project delivery, in
which detailed design and construction are combined into a single phase in the project
development process. See Section 2.3.2 regarding the D&B process.
1. Scoping Phase: The project purpose and need, goals, and objectives are defined in
the scoping phase. Stakeholders are identified, and a project manager is assigned
to assemble the project team based on the relevant disciplines involved in the
project. The project team defines project deliverables, estimated budget, and
schedule for completion of the study and design of the project. The team conducts
a field investigation of the project to identify potential problems including impacts
to sensitive sites, constructability issues, level of outreach, and method of project
delivery.
2. Conceptual Design: During the conceptual design, strategies that could address the
problem including traffic management, alternative transportation routes and
modes, physical improvements, and other measures are identified, studied,
analyzed, and evaluated. If all strategies other than physical improvement prove
insufficient to address the problem, physical improvement will be recommended.
Relevant information including forecast traffic data and topographic survey
information will be obtained. Alternative improvement concepts will be
developed, analyzed, and evaluated based on project goals and objectives, and
presented to stakeholders. The alternative that meets the project objectives will
be submitted for approval and advanced to preliminary design.
The conceptual engineering design phase will include the following:
− Gathering available information on location, size, use of the road, and
pedestrian, bike, and landscape features; visiting the project site to locate
sensitive environmental features; and conducting topographic and utility
surveys.
− Conducting traffic counts and analysis and developing design year traffic
projections.
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− Developing and analyzing alternative conceptual solutions (including
multimodal opportunities) in coordination with stakeholders; preparing
conceptual engineering drawings; evaluating concepts; and identifying the
preferred alternative.
− Establishing a workable geometric design for the preferred alternative that will
work through the final design without major revisions to the horizontal and
vertical geometry; preparing typical cross sections of structures and other
features; and identifying landscaping constraints and opportunities.
− Establishing the type, size, and length of structures, including bridges, retaining
walls, box culverts, and other major structures that may be needed.
− Performing conceptual design of drainage systems, including watershed
delineation, storm sewer system layout, culverts, waterway bridges, and
stormwater management facilities, and utility conflict and mitigationmeasures.
− Performing analysis of constructability and maintenance of traffic and
conceptual design of traffic management and intelligent transportation system
(ITS) plans.
− Establishing limits of right-of-way, identifying land and parcels that need to be
acquired.
− Assessing the environmental impacts of the preferred alternative, obtaining
stakeholders’ approval, and securing the required permits and approvals.
−
Conducting a value engineering review and incorporating its finding into thedesign.
− Developing quantities and estimated construction cost for the project, and
documenting pros and cons of the preferred alternative.
− Conducting mandatory reviews and quality controls subject to approval from
the Overseeing Organization.
3. Preliminary Design: Once the preferred alternative is selected and approved, the
project will be advanced to preliminary design. The preliminary design phase is very
important. Sufficient engineering design details of the selected concept will be
developed and evaluated to verify that there are no unforeseen problems in thedesign. Departures and required permits will be identified and the application
process will begin. A detailed cost estimate and construction schedule will be
developed based on the preliminary design plans. The project delivery method, e.g.,
design, tender, and construct or design and build, will also be decided during the
preliminary design phase. Engineering activities in this phase include the following:
− Design and further refinement of roadway geometry
− Design of drainage systems, erosion and sediment controls, and storm water
management facilities
−
Design of structures and bridges, traffic control features, and ITS− Design of landscaping features and multi-use paths and trails
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− Identification of utility conflicts and relocations options, utility designs, and
utility field inspection
− Conducting constructability analysis, and preparing maintenance of traffic and
construction staging plans
− Conducting and documenting mandatory reviews and quality controls
− Obtaining approval for right-of-way expropriations
− Revising and updating quantities, cost estimates, and schedule
− Applying for and obtaining required permits from the Overseeing Organization
4. Detailed Design: Final design comprises the following activities:
− Finalizing the design and producing final plans for roadways, drainage systems,
erosion and sedimentation control, and stormwater management systems.
− Finalizing the design for and producing final plans for structures and bridges,
traffic control devices/ITS, landscaping, and multi-use facilities, and so on.
− Finalizing right-of-way plans; preparing utility impacts analysis, and producing
utility composite plans for existing utility relocations and for proposed utilities.
− Obtaining all required permits.
− Performing constructability and maintenance of traffic analyses, and preparing
construction staging and traffic management plans.
− Authorizing right-of-way expropriation and utility relocation or installation, or
both
− Making necessary preparations for construction advertisement and tender.
5. Pre-tender Phase: The pre-tender phase includes the following activities:
− Prepare construction cost estimate, specifications, and construction schedule
for the project with sufficient details and milestones based on the final plans
and quantities.
− Secure required permits, certifications, and approvals.
− Prepare an overview of the project for the contract department including
general information, factors considered in preparing cost and schedule, andknown issues that could affect the project, along with supporting
documentation for cost and schedule.
2.3.2 Project Development Process: Design and Build (D&B)
The process for developing plans up to the end of the conceptual design stage for D&B
projects is generally the same as that for a design, tender, and construct project.
Limited investigation and engineering and design can be necessary to identify key risks
and opportunities to be included in the D&B tender. More detailed engineering and
design is not required prior to tender for a D&B project, as it limits the D&B team’s
scope for innovation. However, a value engineering study is recommended for large
projects.
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Once a decision is made to use the D&B delivery method, the project team will use the
conceptual engineering plans to develop the tender documents, including project
limits, scope of work, outline schedule, employer’s requirements, and special
provisions. A cost estimate will need to be prepared to assess tenders. Rights-of-wayneed to be conservative, within reason, at the concept phase for a D&B project to
provide bidders scope for innovation.
Following the concept design, the process for D&B projects differs from the design,
tender, and construct process. Development of preliminary design and construction
plans and construction of the project will be the responsibility of the successful D&B
tenderer’s team. The D&B team will begin mobilization and construction work before
completion of the design stages.
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3 Project Development Processfor Interchange Design Studies(Existing Reconstruction orNew)
Selecting and designing the best-value interchange combines application of the
technical background described above with site- or location-specific knowledge and
data. The importance of interchanges to the functionality of the overall highway
network demands careful study to determine the best solution. The design process
starts with an understanding of the basic goals, objectives, and need for the
interchange project.
3.1 Step 1: Establish Data Collection Requirements andObtain Data
At a minimum, the following data and information are necessary to conduct a study to
determine the appropriate interchange type and to advance it through final
engineering design:
• Design year average daily and design hour traffic forecast for freeway approaches,
crossroad, ramps, and all peak hours turning movements. If the new interchange is
within 4 kilometers (km) of an adjacent interchange, traffic forecast data for that
interchange should be obtained to understand the operational effects on it.
• Aerial photography and base-mapping allowing for planning studies at suitable
scales of typically 1:2500 for concept planning and eventual preliminary
engineering at 1:1000 and 1:500 scales.
• Ownership of land in all quadrants of the proposed location and along the
crossroad.
• Knowledge of important cultural, historic, environmental, mosques, schools, parks
and public safety facilities, or other lands and land uses near the interchange. Note
that awareness of these goes beyond potential right-of-way needs and
encompasses such factors as noise, visual effects, and presence of pedestrians.
• Plans and inspection reports for existing highway and bridge infrastructure at the
proposed location.
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• Plans of known utilities, both above and below ground.
• Data on soil conditions.
3.1.1 Develop Interchange Planning and Design Framework
Key early decisions and actions will affect the progress of the study. The nature of
interchange projects is that many public, governmental, and private stakeholders may
have a direct interest in one or more aspects of the study, including regulatory
permissions and approvals.
3.1.2 Stakeholder Involvement
Key stakeholders are any agency or individual with a direct interest because of the
location of the study, or because of their role in providing information and data, in
reviewing, in issuing permits, or in accepting and approving the project. Early notice to
such stakeholders facilitates their input when needed, thus reducing the time and costto complete the project. Early notice and engagement avoids problems associated with
unforeseen conflicts.
For major interchange projects or projects in urban areas affecting many stakeholders,
best practice is to formally engage them in early meetings and dialogue, referred to as
chartering. Table 3.1 summarizes suggested representative stakeholders and both the
issues and potential inputs they may provide to the project.
Table 3.1 Typical Stakeholders and Their Issues for Interchange Projects
Stakeholder Issue or Concern
Overseeing Organization:
Design
Project is designed in accordance with standards; adequate review and
approval of Departures.
Overseeing Organization:
Traffic
Project will operate as intended (LOS, safety performance); operation of
traffic controls.
Overseeing Organization:
Construction
Project bids will be acceptable; constructability within schedule and
budget.
Overseeing Organization:
Maintenance
Need for maintenance of all project elements, safety of maintenance
workers.
Overseeing Organization:
Public Parks
Landscaping of public places, planting of trees, traffic island planting, and
maintenance of landscaping and public parks.
Transit Agency
Incorporation of bus stops or light rail/metro stations near interchange
on crossroad; safety of pedestrians.
Utilities Need for and timing of relocated utilities.
Adjacent Landowners
Potential acquisition, noise from traffic, dust and other impacts of
construction, changes in access to their properties, visual effects, timing,
and length of construction.
Highway Users Safety of the interchange, reductions in delay or travel time after
construction, detours, or delays during construction.
Ministry of Environment Protection of proximate environmental resources, permitting, and
approvals.
Law Enforcement Ability to enforce traffic laws, safety of the interchange.
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A chartering meeting may include the following:
• Background introduction of the need for the project
• Introduction of key project staff, including contact information• Presentation of the planned public outreach program
• Intended schedule for the study, design, and construction
• Opportunity for stakeholders to present issues or concerns at the outset
• Discussion of issues regarding property or interest that may not be known from
public records
3.1.3 Develop Project Planning and Design Criteria
The entity conducting the study, consulting with appropriate agency stakeholders
including the Overseeing Organization, should develop, distribute, and present the design
criteria for the project. These should include design speeds of all elements, design year
and basis for design year traffic, design LOS for all elements, design vehicles, drainage
design criteria, and design standards to be used, including specific entrance and exit
design details. At this stage, criteria determined to be appropriate for use that are outside
the QHDM-published criteria are understood to be subject to a Departure. Best practices
are for such criteria to be discussed fully before initiating major work, with concurrence
from or at least notice to the Overseeing Organization of the reasons for the Departure,
and agreement to proceed using the proposed criteria.
3.2 Step 2: Confirm Study Approach, Evaluation Criteria,
and Decision ProcessThe planning and design framework includes an affirmation of the technical approach to
the work. This should be as outlined in the scope of work for the project, but before it
begins, concurrence on methods, data, and necessary assumptions where no data exist
should be reached. Such methods may include capacity and operational analysis methods
that are both large- and small-scale, and quantitative safety analyses.
3.2.1 Determine Evaluation Criteria and Technical Approach
The key technical factors that will drive the selection of one alternative over another
should be identified, which should shape the detail and level of effort in addressing
them. Although every project is unique, the following factors generally will be of
sufficient importance:
• Estimated initial cost of construction
• Measures of traffic service, such as travel time, delays, queuing, and LOS
• Right-of-way acquisitions, including not only cost but also types of businesses,
residences, or other uses affected or displaced
• Accessibility to side roads and private properties
• Environmental issues requiring mitigation
•
Assessment of safety performance• Constructability
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To the extent possible, those charged with making the final decision on which
alternative to select should communicate the relative importance of these factors.
3.2.2 Develop Design Year Traffic and Select Most Likely AlternativesThe next step is to develop design year traffic as intended, and then, with reference to
the guidance presented in Part 9, identify the most likely reasonable alternatives for
the location. These will depend on the functional classification of each road, design year
traffic, general knowledge of the spatial and quadrant-specific requirements for each
interchange form, and understanding of the most likely or only vertical
crossroad/freeway relationship.
For service interchange projects, there may as many as six reasonable options
representing basic forms and variants thereof. For system interchange projects, at least
three and often more solutions may be worthy of study.
3.3 Step 3: Conduct Interchange Type StudiesThe process for efficient and complete interchange studies is stepped and begins with
as many likely alternatives as are evident, then proceeds through increasing level of
technical detail to screen those down to a single preferred alternative.
3.3.1 Concept Engineering Design
The following is completed is for each concept identified for study:
• Size each interchange concept using design year traffic and quick capacitytechniques. Sizing refers to determining the preliminary numbers of lanes for
ramps, ramp terminal intersections, roundabouts, crossroad bridges, auxiliary lanes
on freeway.
• Develop concept level design in plan view over aerial photography. A sufficiently
skilled and knowledgeable designer can develop appropriate geometry without
having to conduct profile studies. The designer can estimate limits of bridges and
retaining walls, approximate right-of-way, and potential encroachments on
properties. Figure 3.1 is an example of such a concept.
• Using this information, an approximate, comparative construction cost estimatecan be prepared. As the interchanges should be operationally comparable, the
process of screening focuses on costs, right-of-way, and environmental or special
local issues.
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Figure 3.1 Example Single-line Concept Plan View over Aerial
3.3.2 Stakeholder Review and Screening
Depending on the project’s sensitivity and importance, conduct external stakeholder or
public meetings to present the alternatives under consideration and their attributes.
Such meetings may apprise designers of previously unknown specific issues or impacts
associated with one or more alternatives.
Consult with agency and regulatory stakeholders. As a minimum, they should
communicate fatal flaws or issues that may, if not resolved, present major schedule or
cost impacts not previously apparent. They may express views representing their
agency on the alternatives that the Overseeing Organization should consider.
Decision-makers can then screen the alternatives down to the most reasonable two, or
at most three.
For simple two-level service interchange projects, it may be possible to select the best
value solution. For multilevel system interchanges with complex geometry and
significant costs, the next step is generally required.
3.4 Step 4: Functional Geometric Design of ScreenedAlternativesAn alternative proceeding to this stage should have no environmental or other
problems that would hinder its selection. Assuming more than one alternative remains
viable, designers next conduct preliminary geometric design studies at an acceptable
scale as agreed with the Overseeing Organization in three dimensions. Plan view,
profile in the detailed design stage, and intersection design studies are conducted. The
latter include details such as intersection or roundabout geometry, left- and right-turn
lengths, signal phasing, and operations. Concept level bridge studies determine mostlikely type, depths, widths, and ancillary structures such as retaining walls. To facilitate
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a decision, additional concept studies of drainage, lighting, and signing may be
conducted. With three-dimensional plans, earthwork can be developed as part of the
detailed design, enabling firm estimates of right-of-way acquisition. At this stage,
differences in construction staging or maintenance of traffic along the freeway shouldbe understood and documented.
This phase of work may include micro-simulation studies of freeway and or crossroad
operations. These can provide more complete measures of traffic performance, which
may help differentiate between, say a partial cloverleaf (PARCLO) interchange and a
diamond, or between a signalized diamond and a roundabout diamond interchange.
Finally, quantitative safety analyses using the Highway Safety Manual (HSM; American
Association of State Highway and Transportation Officials [AASHTO], 2011) can be
performed to develop comparisons of the difference in predicted crash types and
severities.
At this level of design, all necessary significant Departures should be known. They
should be fully discussed to the point that, should an alternative be selected, there is
confidence that any Departures associated with it will be found acceptable.
3.5 Step 5: Select Preferred Alternative, Document andDevelop Final Engineering PlansWith all the above detail, there is sufficient technical information for the Overseeing
Organization to determine a preferred alternative. Once a decision is made, completion
of all final engineering plans can proceed.
Documentation of the recommended plan, including the following, provides the
background to explain and defend the project:
• Stakeholders consulted and their input
• Alternatives considered, including summaries of those screened out
• Design plans and supporting technical information on alternatives with completed
functional design
•
Construction cost models, assumptions and estimates
• Environmental clearances and other permits required or obtained
• Departures subject to final approval
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4 Projects Involving ExistingRoads
The Overseeing Organization may undertake projects involving existing roads. There
are four main reasons for such projects, associated with modes of travel:
• An observed or expected traffic operational problem, such as bottlenecks or low
LOS
• An observed safety problem, as identified through a science-based assessment of
crash frequency and severity
• An identified need to provide access to a new adjacent development
• Pavement or other road infrastructure in a state of disrepair
Projects involving existing roads are named 3R for Resurfacing, Restoration, and
Rehabilitation. Examples of 3R projects include:
•
Pavement that has reached its useful life and requires complete replacement,including potentially the subgrade, shoulders and curbing
• Removal of a bituminous overlay to a concrete pavement and replacement with a
new overlay
• Replacement of roadside barriers such as guardrail
• Bridge redecking
• Major repairs or replacements to a bridge substructure
Other certain work efforts related to infrastructure condition are fundamentally
preventative maintenance activities. These may include minor pavement repairs suchas seal coats, full-width patching, crack sealing, and thin plant mix resurfacing for
sealing of the pavement surface, correcting minor surface irregularities, and other
similar repairs. Curb repairs or replacement, replacement of drainage inlets, and other
similar activities are also fundamentally preventative maintenance in nature. These
repair types are an important part of the Overseeing Organization’s overall mission.
Maintenance repair activities are not considered to be 3R or reconstruction projects.
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4.1 Unique Characteristics of Projects InvolvingExisting RoadsProjects involving existing roads fundamentally differ from those involving new roads
for several important reasons. First, there is a proven and observable set of traffic
operational and safety performance measures for an existing road. These should be
referenced to determine the nature and extent of any problem.
Second, in most cases there is fixed right-of-way for the existing road, around which
land development typically has occurred. In urban areas development typically will
involve buildings and other private infrastructure immediately contiguous with the
right-of-way. Projects involving existing roads require designers to understand the
context and to be creative in developing solutions within the right-of-way, because any
major realignment or widening has the potential for producing substantial impacts to
many property owners and stakeholders.
A third unique aspect of projects involving existing roads is they have in place a roadway
with fixed geometric conditions. The road will have been designed to standards
employed at the time of its initial construction. Some roads may predate the 1997
QHDM. As this edition of the QHDM includes some revisions to geometric design
criteria based on research advances, it is possible that an existing road may have
geometric features that do not meet the updated, current version of QHDM design
standards.
Design standards are a means to an end. The end desired is measurable or expected
performance with respect to either safety, operations, or both. An existing geometric
feature or dimension that does not meet current design criteria does not automatically
require reconstruction to meet such criteria. Such practice is a sub-optimal use of
resources and may produce unnecessary inconvenience to road users and stakeholders
affected by construction activities. Decisions under a best-value approach shall be
based on a review and analysis of the existing roadway’s performance.
Projects of the above nature will be considered as either 3R projects or reconstruction
projects. The Overseeing Organization will make the determination for project
eligibility for 3R treatment using the criteria discussed below.
4.2 Design of Reconstruction ProjectsReconstruction projects will be those for any of the following:
• The demonstrated project need goes beyond mere infrastructure repair, to include
a known quantitative safety problem or a known operational problem.
• The project involves the redesignation or reclassification of a roadway to serve new
types of trips or travel not previously included along the route, such as bike paths
or dedicated transit only lanes; widening; conversion of intersection type such as
roundabout to signalized intersection.
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• The project is bridge replacement which specifically includes improvements to
vertical clearance.
• The project converts a temporary road to a permanent road.
• The Overseeing Organization determines that the project shall not be eligible for
3R treatment, as described above.
Reconstruction projects will involve substantial revision to the functionality and three-
dimensional character of the road. Reconstruction projects shall be designed and
reconstructed using the design criteria in the QHDM.
Challenges unique to reconstruction versus new construction projects include these:
• Right-of-way typically is limited, with adjacent development already established.
Even minor strip acquisitions may create significant damage to adjacent properties,
in some cases necessitating entire acquisition.
• In most cases, it will be necessary to maintain traffic flow along the roadway during
reconstruction. This includes through traffic, intersection movements, and access
to business, retail, and residential land uses. Existing underground utilities are in
place. These constraints will influence the suitability of design solutions, and may
limit the ability to make more than minor changes to vertical alignment.
The full design process for new roads applies to reconstruction projects, including
development of design alternatives and evaluation of potential Departures from
Standards. Departures may be significant for such projects.
4.2.1 Relationship of Safety Performance to Design Elements
The acceptance of Departures from Standards generally will be greater for reconstruction
projects. A project may be designated for reconstruction based on a review of its crash
history, but the types and locations of crashes may be such that certain design elements
or locations along the road may not require full geometric redesign. Thus, for example,
a decision may be made to flatten a horizontal curve but to retain the vertical
alignment, even though there are nominally substandard elements.
Table 4.1 summarizes the known relative importance of roadway elements in safety
performance, crash frequency, and severity of different roadway types and contexts.
Not every geometric element is of equal importance in influencing safety performance.
Moreover, the contribution to safety performance of an element varies by type of road.
Table 4.1 serves as a reference in making decisions on retaining existing road geometry
to avoid major costs and conflicts. Refer to the AASHTO HSM (2011) for more details
on the specific elements and road types.
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Table 4.1 Relative Relationship of Geometric Design Features to Crash
Frequency or Severity by Type of Road
Roadway Design Elements
Road Type and Intersections
R u r a l 2 - l a n e
R u r a l M u l t i l a n e
M u l t i l a n e U r b a n
A r t e r i a l s a n d
C o l l e c t o r s
F r e e w a y
U n s i g n a l i z e d
i n t e r s e c t i o n
S i g n a l i z e d
i n t e r s e c t i o n
R o u n d a b o u t
Cross Section
Lane Width — — — —
Cross Slope — — — — —
Shoulder Width ✓ ✓ — ✓ — — —
Shoulder Type (Paved, Unpaved) — — — —
Presence of Rumble Strips ✓ ✓ — ✓ — — —Sideslope — ✓ — — —
Clear Zone ✓ ✓ — ✓ — — —
Presence of Roadside Barrier ✓ ✓ — ✓ — — —
Presence of Median NA ✓ ✓ ✓ — — —
Width of Median NA ✓ ✓ ✓ — — —
Alignment
Horizontal Curvature (Radius) ✓ ✓ — ✓ NA NA ✓
Length of Curve ✓ — NA NA NA
Presence of Spiral ✓ — NA NA NA
Superelevation — — — NA NA NA
Grade ✓ — — NA NA NA
Length of Vertical Curve — — — NA NA NA
Stopping Sight Distance — — — NA NA NA
Presence of Weaving Sections NA NA NA ✓ NA NA NA
Length of Weaving Sections NA NA NA ✓ NA NA NA
Location of Ramps (Left vs. Right) NA NA NA ✓ NA NA NA
Other
Frequency of Driveways ✓ — ✓ NA NA NA NA
Frequency of Intersections ✓ ✓ ✓ NA NA NA NA
Type of Intersections (TrafficControl)
— — — NA NA NA NA
Intersection Elements
Intersection Sight Distance NA NA NA NA ✓ — —
Number of Legs/Approaches NA NA NA NA ✓ ✓ ✓
Skew Angle NA NA NA NA ✓ ✓ —
Presence of Left-Turn Lanes NA NA NA NA ✓ —
Presence of Right-Turn Lanes NA NA NA NA —
KEY: Significant Effect Minor Effect — No Effect NA Not applicable
Based on AASHTO HSM (2010).
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4.2.2 Risk Management Guidelines
Safety performance related to roadway design elements and dimensions is a
continuum. One can estimate safety risk by quantifying the three most important
factors that relate to crash risk on all road types:
• How close the dimension or value is to the specified minimum value
• Traffic volume exposed to the element
• Length of roadway over which the element occurs
Marginal differences in a design dimension will have at most marginal differences in
the expected safety performance of the road if any. Figure 4.1 illustrates this concept.
Source: Fambro, et al. Determination of Stopping Sight Distances, NCHRP Report 400.
Figure 4.1 Conceptual Relationship between Available Sight Distance and Safety
at Crest Vertical Curves
Figure 4.1 is taken from research on SSD and is illustrative only. The concepts below
apply not only to SSD but also to all other geometric elements.
Existing values for sight distance that do not meet the standard but are short by only a
small amount will produce little if any practical increase in actual risk. Only when the
amount of the deficiency is large might a meaningful increase in crash risk be expected.
4.2.2.1 Effective vs. Selected Design Speed
Taking the minimum design value per QHDM standards as a reference point, a useful
measure of risk is the difference between the “effective” design speed of existing
geometry for a design element, such as, horizontal or vertical curvature, and the
selected design speed. This difference is referred to as delta V ( Δ V). Geometry that may
not meet the minimum standard but that is very close to it, with a small value for delta
V, can be considered as presenting minimal risk.
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The following guidelines apply and may be used in making departure decisions:
• Low risk alignment has a Δ V of 10 kilometers per hour (kph) or less.
• Moderate risk alignment has a Δ V of 11 kph to 20 kph.• High risk alignment has a Δ V of greater than 20 kph.
4.2.2.2 Traffic Volume Exposure
Substantive safety risk is also proportional to the traffic volume on the roadway. For
example, the predicted crash frequency per km for a 2-lane rural highway is 0.15 per
year for a volume of 1,000 vpd, and 2.5 per km for the same road with 15,000 vpd.
Whatever the effect of a geometric element may be, the risk is clearly different
depending on the traffic volume exposure. This same concept applies to intersections,
which are point locations in terms of crash frequency.
4.2.2.
Recommended