qhdm vol1 part02 planning octfinal

8/17/2019 QHDM Vol1 Part02 Planning OctFinal

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Volume 1

Part 2Planning


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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

ا

ز

‐ Qatar Highway Design Manualدو ط ر د اطق و ط)ات و QHDMدو (

) ير

و

ا

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Qatar Traffic Control Manual ‐ QTCMر

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كو

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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.


Traffic

Project will operate as intended (LOS, safety performance); operation of

traffic controls.


Construction

Project bids will be acceptable; constructability within schedule and

budget.


Maintenance

Need for maintenance of all project elements, safety of maintenance

workers.


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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VOLUME 1 PART 2

PLANNING

PAGE 26 VOLUME 1

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.

qhdm vol1 part02 planning octfinal

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