Highway Engineering
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Persons
Martin Rogers BE, MEngSc, PhD, BA(Public Ad), CEng, MICE, MRTPI, Chartered Engineer and Chartered Town Planner, has worked in private practice as well as in local authorities, and was a member of the Dublin Transport Initiative Study Team that devised the first integrated transportation plan for the Dublin city region. He joined the permanent staff at the Dublin Institute of Technology in 1993, was Assistant Head of School with responsibility for first year engineering from 2010 to 2014, and is currently a Senior Lecturer in the School of Civil and Structural Engineering.
Bernard Enright BE, MSc, PhD originally qualified as a civil engineer and worked in information technology in engineering and in the financial markets for 25 years. He joined the School of Civil and Structural Engineering at Dublin Institute of Technology as a Lecturer in Civil Engineering in 2003, where he chairs the Bachelor of Engineering Technology degree programme in Civil Engineering. He completed his PhD on the subject of traffic loading of highway bridges in 2010, and has published extensively on this and related topics.
Content
Preface xii
Sources xiv
1 The Transportation Planning Process 1
1.1 Why are highways so important? 1
1.2 The administration of highway schemes 1
1.3 Sources of funding 2
1.4 Highway planning 3
1.5 The decision making process in highway and transport planning 9
1.6 Summary 14
1.7 References 15
2 Forecasting Future Traffic Flows 16
2.1 Basic principles of traffic demand analysis 16
2.2 Demand modelling 17
2.3 Land use models 19
2.4 Trip generation 20
2.5 Trip distribution 24
2.6 Modal split 35
2.7 Traffic assignment 40
2.8 A full example of the four stage transportation modelling process 46
2.9 Concluding comments 52
2.10 References 52
3 Scheme Appraisal for Highway Projects 53
3.1 Introduction 53
3.2 Economic appraisal of highway schemes 54
3.3 CBA 55
3.4 Payback analysis 68
3.5 Environmental appraisal of highway schemes 70
3.6 The New Approach to Appraisal 76
3.7 NATA Refresh (Department for Transport, 2008) 82
3.8 Summary 83
3.9 References 84
4 Basic Elements of Highway Traffic Analysis 85
4.1 Introduction 85
4.2 Surveying road traffic 85
4.3 Journey speed and travel time surveys 91
4.4 Speed, flow and density of a stream of traffic 96
4.5 Headway distributions in highway traffic flow 103
4.6 Queuing analysis 109
4.7 References 119
5 Determining the Capacity of a Highway 120
5.1 Introduction 120
5.2 The 'level of service' approach using Transportation Research Board (1994) 120
5.3 Methodology for analysing the capacity and level of service of highways within Transportation Research Board (2010) 134
5.4 The UK approach for rural roads 159
5.5 The UK approach for urban roads 162
5.6 Expansion of 12 and 16 h traffic counts into AADT flows 165
5.7 Concluding comments 167
5.8 References 168
6 The Design of Highway Intersections 169
6.1 Introduction 169
6.2 Deriving DRFs from baseline traffic figures 170
6.3 Major/minor priority intersections 171
6.4 Roundabout intersections 185
6.5 Basics of traffic signal control: Optimisation and delays 198
6.6 Concluding remarks 218
6.7 References 218
7 Geometric Alignment and Design 220
7.1 Basic physical elements of a highway 220
7.2 Design speed and stopping and overtaking sight distances 222
7.3 Geometric parameters dependent on design speed 231
7.4 Sight distances 232
7.5 Horizontal alignment 236
7.6 Vertical alignment 248
7.7 References 262
8 Highway Pavement Materials and Loading 263
8.1 Introduction 263
8.2 Soils at subformation level 265
8.3 Traffic loading 270
8.4 Materials within flexible pavements 275
8.5 Materials in rigid pavements 282
8.6 References 286
9 Structural Design of Highway Pavements 287
9.1 Introduction 287
9.2 Pavement components: Terminology 288
9.3 Foundation design 290
9.4 Pavement design 301
9.5 References 313
10 Pavement Maintenance 315
10.1 Introduction 315
10.2 Pavement deterioration 316
10.3 Compiling information on the pavement's condition 317
10.4 Forms of maintenance 328
10.5 References 332
11 The Highway Engineer and the Development Process 334
11.1 Introduction 334
11.2 Transport assessments 335
11.3 Travel plans 341
11.4 Road Safety Audits 346
11.5 References 355
12 Defining Sustainability in Transportation Engineering 357
12.1 Introduction 357
12.2 Social sustainability 357
12.3 Environmental sustainability 357
12.4 Economic sustainability 358
12.5 The four pillars of sustainable transport planning 358
12.6 How will urban areas adapt to the need for increased sustainability? 360
12.7 The role of the street in sustainable transport planning 361
12.8 Public transport 371
12.9 Using performance indicators to ensure a more balanced transport policy 374
12.10 A sustainable parking policy 392
12.11 References 395
Index 397
Chapter 1
The Transportation Planning Process
1.1 Why are highways so important?
Highways are vitally important to a country's economic development. The construction of a high-quality road network directly increases a nation's economic output by reducing journey times and costs, making a region more attractive economically. The actual construction process will have the added effect of stimulating the construction market.
1.2 The administration of highway schemes
The administration of highway projects differs from one country to another, depending on social, political and economic factors. The design, construction and maintenance of major national primary routes such as motorways or dual carriageways are generally the responsibility of a designated government department or an agency of it, with funding, in the main, coming from central government. Those of secondary importance, feeding into the national routes, together with local roads, tend to be the responsibility of local authorities. Central government or an agency of it will usually take responsibility for the development of national standards.
Highways England is an executive organisation charged within England with responsibility for the maintenance and improvement of the motorway/trunk road network. (In Ireland, Transport Infrastructure Ireland, formerly the National Roads Authority, has a similar function.) It operates on behalf of the relevant government minister who still retains responsibility for overall policy, determines the framework within which the agency is permitted to operate and establishes its goals and objectives and the time frame within which these should take place.
In the United States, the US Federal Highway Administration has responsibility at the federal level for formulating national transportation policy and for funding major projects that are subsequently constructed, operated and maintained at the state level. It is one of nine primary organisational units within the US Department of Transportation (USDOT). The Secretary of Transportation, a member of the President's cabinet, is the USDOT's principal.
Each state government has a department of transportation, which occupies a pivotal position in the development of road projects. Each has responsibility for the planning, design, construction, maintenance and operation of its federally funded highway system. In most states, its highway agency has the responsibility for developing routes within the state-designated system. These involve roads of both primary and secondary statewide importance. The state department also allocates funds to local government. At the city/county level, the local government in question sets design standards for local roadways and has the responsibility for maintaining and operating them.
1.3 Sources of funding
Obtaining adequate sources of funding for highway projects has been an ongoing problem throughout the world. Highway construction has been funded in the main by public monies. However, increasing competition for government funds from the health and education sector has led to an increasing desire to remove the financing of major highway projects from such competition by the introduction of user or toll charges.
Within the United Kingdom, the New Roads and Street Works Act 1991 gave the Secretary of State for Transport the power to create highways using private funds, where access to the facility is limited to those who have paid a toll charge. In most cases, however, the private sector has been unwilling to take on substantial responsibility for expanding the road network within the United Kingdom. Roads tend still to be financed from the public purse, with central government being fully responsible for the capital funding of major trunk road schemes. For roads of lesser importance, each local authority receives a block grant from central government that can be utilised to support a maintenance programme at the local level or to aid in the financing of a capital works programme. These funds will supplement monies raised by the authority through local taxation. A local authority is also permitted to borrow money for highway projects but only with central government's approval.
Within the United States, fuel taxes have financed a significant proportion of the highway system, with road tolls being charged for the use of some of the more expensive highway facilities. Tolling declined between 1960 and 1990, partly because of the introduction of the Interstate and Defense Highways Act in 1956, which prohibited the charging of tolls on newly constructed sections of the interstate highway system, and because of the wide availability of federal funding at the time for such projects. Within the past 10 years, however, the use of toll charges as a method of highway funding has returned.
The question of whether public or private funding should be used to construct a highway facility is a complex political issue. Some feel that public ownership of all infrastructures is a central role of government and under no circumstances should it be constructed and operated by private interests. Others take the view that any measure that reduces taxes and encourages private enterprise should be encouraged. Both arguments have some validity, and any responsible government must strive to strike the appropriate balance between these two distinct forms of infrastructure funding.
Within the United Kingdom, the concept of design-build-finance-operate (DBFO) is gaining credence for large-scale infrastructure projects formerly financed by government. Within this arrangement, the developer is responsible for formulating the scheme, raising the finance, constructing the facility and then operating it in its entire useful life. Such a package is well suited to a highway project where the imposition of tolls provides a clear revenue-raising opportunity during its period of operation. Such revenue will generate a return on the developer's original investment.
Increasingly, highway projects utilising this procedure do so within the private finance initiative (PFI) framework. Within the United Kingdom, PFI can involve the developer undertaking to share with the government the risk associated with the proposal before approval is given. From the government's perspective, unless the developer is willing to take on most of this risk, the PFI format may be inappropriate, and normal procedures for the awarding of major infrastructure projects may be adopted.
1.4 Highway planning
1.4.1 Introduction
The process of transportation planning entails developing a transportation plan for an urban region. It is an ongoing process that seeks to address the transport needs of the inhabitants of the area and with the aid of a process of consultation with all relevant groups strives to identify and implement an appropriate plan to meet these needs.
The process takes place at a number of levels. At an administrative/political level, a transportation policy is formulated, and politicians must decide on the general location of the transport corridors/networks to be prioritised for development, on the level of funding to be allocated to the different schemes and on the mode or modes of transport to be used within them.
Below this level, professional planners and engineers undertake a process to define in some detail the corridors/networks that comprise each of the given systems selected for development at the higher political level. This is the level at which what is commonly termed a transportation study takes place. It defines the links and networks and involves forecasting future population and economic growth, predicting the level of potential movement within the area and describing both the physical nature and modal mix of the system required to cope with the region's transport needs, be they road, rail, cycling or pedestrian based. The methodologies for estimating the distribution of traffic over a transport network are detailed in Chapter 2.
At the lowest planning level, each project within a given system is defined in detail in terms of its physical extent and layout. In the case of road schemes, these functions are the remit of the design engineer, usually employed by the roads authority within which the project is located. This area of highway engineering is addressed in Chapters 4-8.
The remainder of this chapter concentrates on the systems planning process - in particular, the travel data required to initiate the process, the future planning strategy assumed for the region that will dictate the nature and extent of the network derived, a general outline of the content of the transportation study itself and a description of the decision procedure that will guide the transport planners through the system process.
1.4.2 Travel data
The planning process commences with the collection of historical traffic data covering the geographical area of interest. Growth levels in past years act as a strong indicator regarding the volumes one can expect over the chosen future time, be it 15, 20 or 30 years. If these figures indicate the need for new/upgraded transportation facilities, the process then begins to consider what type of transportation scheme or suite of schemes is most appropriate, together with the scale and location of the scheme or group of schemes in question.
The demand for highway schemes stems from the requirements of people to travel from one location to another in order...
