Planning of Roads and Highways
Planning Tools and Analysis Methods
|Regional and Local Economy and Demographics||Design Standards|
|Current Transport Conditions||Costing|
|Data and Information Management||Benefits and Impacts|
|Management Systems||Selected References|
Previous sections have described the establishment of clear and logical processes for conducting road and highway planning. This section describes analysis tools and methods that are used to inform the various steps of the planning process. These tools and methods support planning efforts at all levels including system, corridor, and project planning. Established procedures to collect, manage, and analyze data are critical in identifying road and highway needs; evaluating the benefits and costs of potential projects; and comparing the effects of various projects and programming decisions.
Regional and Local Economy and Demographics
Compiling regional and local economic and demographic data is an important first step in assessing transport needs. Data on population by geographic area provide a key indicator of the market served by the road or highway, and thus the potential demand. Additional demographic data, such as income, automobile ownership, and children and elderly population can further help identify personal transport needs (low automobile ownership, for example, might indicate a high importance of public transit service and non-motorized traffic accommodation.) Economic data, such as number of establishments and total employment in an area, can indicate major destinations for goods movement and business travel. Economic data by type of industry is important because different industries will have different needs for transport services. Finally, economic and demographic data can serve as a basis for forecasting traffic flows over an improved transport network (see "Demand Forecasting").
The extent and quality of existing data sources varies considerably from country to country. Most countries will have some type of national census from which population and demographic data can be obtained. Many countries also collect data on total establishments, employment, and sales by industry on a regular basis although the level of geographic detail varies. Regardless of the extent of existing data, it is important that the road and highway administration establish the management of these data as a routine part of their work.
In cases where national and local sources do not contain the required data, or where these sources have not been recently updated, satellite imagery or aerial photography can be used to estimate population and economic data. Photographs can be analyzed to determine the location of housing units and therefore to estimate the population of an area. Photographs can also be used to locate concentrations of businesses as well as major industries.
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Current Transport Conditions
An inventory of the location, extent, and quality of existing transport facilities is a key step in assessing future transport needs. A road data bank should be established and updated on a regular basis. Key characteristics of roads and highways include functional class and other route designations (national, regional, or local jurisdiction; truck and/or bus route), limited-access, number of lanes, lane and shoulder widths, design speeds, capacity, and pavement type and condition. Bridges are often a limiting factor in transport system performance, and an inventory of bridges should include factors such as road served, location, width, load rating, vertical clearance, age, and structural condition. The location of intermodal terminals including ports, airports, and rail terminals, along with the characteristics of roads accessing these terminals (especially suitability for truck traffic), are also key data elements.
Unless a regular data collection and update system is in place, it is important to recognize that the information may not be current. This is particularly true for factors such as pavement conditions (which may deteriorate) and for improvements undertaken by one administration that are not transferred to another administration's records. Therefore, if the existing facility inventory data is not current, procedures to update these data need to be devised. A combination of interviews with local professionals, site visits and field data collection and other appropriate means can be used to jump-start the process. As with population and industry data, satellite imaging or aerial photography can also serve as a data source on the location and nature of existing transport facilities.
Data on transport system performance and use provide a counterpart to data on facilities. System performance data are essential to the economic analysis of transport investments and to the analysis of other project benefits and impacts. One key type of system performance data includes traffic volumes by facility and vehicle type. A regular monitoring program should be established to count traffic volumes by type of vehicle on key roads and highways. Data on traffic volumes can be used in conjunction with facility information to evaluate level-of-service. Road traffic volume data can also be used in conjunction with flow data for railways, waterways, and air traffic to identify major corridors for people and goods movement. Click here for a description of a national traffic-monitoring program. For guidance on traffic monitoring techniques and sampling methods, see Items 2 and 3 in the "Selected References" section of this document.
Another important type of system performance data is crash locations and characteristics. Key crash characteristics include the location, time, and environmental conditions of the crash; vehicles and persons involved; nature and extent of injuries and property damage; and contributing factors. Crash reporting practices vary both at a national and local level. If local or national databases do not exist, interviews with public and private transport operators, local transport officials, or law enforcement officials can help pinpoint frequent locations of crashes and other incidents. Safety councils of the police, highway department, and other agencies, established to coordinate accident response procedures, may also serve as a source of data. Click here to see an example of a national and regional crash data reporting system.
Information on the location and severity of crashes can be used to identify and prioritize facilities for safety-related improvements. Information on conditions, contributing factors and outcomes is also valuable in assessing the effectiveness of various actions to improve safety. Data on crash frequency by location should be used in conjunction with measures of exposure (for example, traffic volumes) to assess relative hazards and prioritize locations for improvement.
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Data and Information Management
Economic, demographic, facility condition, and systems performance data may be kept in a variety of forms, including paper maps, tabular databases, and geographic information systems (GIS) software. Emerging computer and software technology can greatly enhance the management and analysis of transportation-related data.
The use of GIS to manage data can simplify the analysis of transport systems and can enhance the decision-making process. GIS are software tools for managing, analyzing, and displaying data in a spatial framework. GIS contain data related to location points, lines (commonly roadway links and corridors), and polygons (surface areas and analysis zones). Analysis tools that are part of GIS software packages can be used to relate these data, for example, to calculate the population within two kilometers of a given highway route. In addition to providing a convenient electronic means of storing and analyzing data, GIS can be used to produce displays and printed maps. Any number of attributes (for example, roadway locations, traffic volumes, and major industries) can be plotted on the same map. For links to examples of GIS applications, click here.
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Management SystemsManagement systems include software programs and related processes to assist in managing and analyzing various components of the transport system. Performance management systems focus on factors such as system safety, congestion and mobility, and intermodal connections. Asset management systems help agencies manage physical assets including bridges, pavement, public transit equipment and facilities, and real estate.
Management systems are based on inventories of existing facilities and performance characteristics. GIS and shared network databases are commonly used to give multiple users access to these systems and to facilitate the management, analysis, and display of data. Management systems can allow users to define and view existing conditions and performance measures; define acceptable performance standards; and identify deficiencies by comparing existing facility conditions with standards. Management systems also include analytical tools to evaluate the impacts of alternative investment strategies on system condition and performance. For example, Pavement Management Systems (PMS) can be used to select the best combination of preventive maintenance and capital improvement projects that can be purchased at a given spending level, in order to minimize life-cycle costs. See the following examples of management systems:
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Future "demand" or level of use of the transport system may change as a result of two types of factors:
In addition to increasing overall traffic, transport investments may affect the distribution of existing traffic by changing the relative cost of travel on various transport routes.
Demand forecasting involves a set of analytical procedures to estimate future levels of transport system use as a result of changes in population characteristics, economic activity, and transport network conditions, and of subsequent changes in travel patterns. Demand forecasting serves different purposes depending upon the level of the study. For strategic planning, forecasts are needed to evaluate the overall viability of alternative strategies and the demand for individual components of these strategies. For corridor planning, forecasts are needed to determine the adequacy of existing facilities and services in the corridor and the potential need for expanding these facilities and services. For facility planning, forecasts are needed to determine the appropriate capacity of new facilities that may be built and of existing facilities that are being considered for expansion.
Methods for demand forecasting can range from very simple to very complex. At the most basic level, past trends in traffic growth can be extrapolated to predict future levels of traffic in any given year. A more sophisticated approach will estimate future traffic based on projections of the underlying drivers of traffic - for example population, economic activity, vehicle ownership. Either of these methods can be applied at a regional or corridor level to provide a rough estimate of future transportation demands. More sophisticated methods of forecasting the underlying variables are likely to result in more accurate traffic forecasts.
The population and employment forecasts provide a basis for estimating future "background" flows on the system. The future transportation network can then be varied to describe proposed improvements to the road and highway system. This will predict the changes in the distribution of future traffic over the network, and to some extent will predict increases in travel caused by reductions in transportation costs. Demand forecasting methods have primarily been developed for urban applications, but these same methods are increasingly being adapted for state or regional planning. See the following references for additional information on demand forecasting:
A World Bank study group is also looking at advanced travel forecasting models and their potential application to regional road and highway planning.
Various surveys and counts must be performed to support travel demand forecasting using four-step or other network-type models. Basic data requirements include:
See Items 5 and 6 in the "Selected References" section of this document to read about other types of surveys, such as employer-based surveys and transit on-board surveys, which may also be used to support modeling. Click here to display or download the Travel Survey Manual prepared by Cambridge Systematic, Inc. for the U.S. Department of Transportation, Federal Transit Administration, Federal Highway Administration, Office of the Secretary, and the U.S. Environmental Protection Agency (July 1996), which contains a detailed description of the various types of travel surveys and how to implement them, and also to view samples of different types of travel surveys.
Demand forecasting models originally focused on personal travel, but recently the importance of forecasting freight and other commercial vehicle traffic has received increasing attention. A noteworthy difference between freight and passenger travel analysis is that in the case of freight analysis, interviews with logistics coordinators at a sample of larger businesses and freight shipping companies can often provide a good picture of the primary freight travel patterns and needs. Passenger travel patterns, in contrast, vary at the level of the individual and random, large-sample surveys of the population are required.For an overview of the factors influencing freight travel, and basic methods for forecasting this travel, click here. For additional discussion of planning considerations and forecasting methods for freight travel, see Item 7 in the "Selected References" section of this document.
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Design standards describe characteristics of the roadway geometry, such as lane width, radius of curves, and acceptable grade, as well as traffic control devices including signals, signage, and pavement markings. The establishment of design standards for roadways promotes safety and efficiency, since the standards are based on established research on the safety and performance implications of various design features. Uniform designs further promote safety by increasing the predictability of the driving environment, so that the road user knows what to expect in any given situation.
Traffic control devices, including signals, signs, and pavement markings, should be applied in a uniform manner and should have uniform design and meanings wherever they are applied. Design standards for roadway geometry, while also important, can have somewhat more flexibility and can vary depending upon the functional class, projected traffic volume, desired design speed, environmental sensitivity, and other considerations. Standards that are reasonable for roads built on flat terrain, for example, may lead to prohibitively expensive construction costs in mountainous areas. Also, roads with low projected traffic volumes generally do not require design standards as strict as those for high-volume roads. Since design standards have a large impact on cost, they should not be set higher than can reasonably be achieved within the highway program budget. Selection of appropriate design standards should be based on a comparison of the costs of achieving these standards with the benefits to users in terms of safety, travel time, and other measures.
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Project costs consist of initial costs, capital costs, and the operating and maintenance (O&M) costs associated with the project. Initial costs include the cost of project planning and design. Capital costs include land acquisition, construction of the road, and installation of signals and other control equipment. O&M costs include routine maintenance of the roadway and control devices and can include other items such as vegetation control, trash cleanup, snow removal, and toll operators' salaries. Also, capital expenditures can affect O&M costs, and the likely impacts of any capital expenditure on O&M costs should be clearly identified and accounted for in the budgeting process. For an overview of costing approaches, click here.
System-level cost estimation is a useful technique for regional road and highway planning. System-level cost estimation uses local project cost experience as the basis for cost estimates of candidate projects and programs. It is primarily useful for long-range planning efforts, in which financially constrained system plans are required but information is not sufficient to estimate detailed quantities and unit costs.
Operating and maintenance cost estimating for road and highway systems generally includes labor, materials, and supplies expenditures that are consumed in operating the system over a given time period, usually a year.
Life cycle costing is an economic assessment of all significant costs of ownership of an asset over its economic life, expressed in equivalent dollars. Life cycle costing requires information on the capital cost of the project, its useful life, and annual O&M costs. Costs are then discounted over the lifetime of the project using an appropriate discount rate. Life cycle costing can assist in setting design and construction standards to minimize total costs over the project lifetime. For example, use of more durable pavement increases construction costs but decreases O&M costs over the project lifetime.Established methods and software are available to analyze these tradeoffs; see the following references:
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Benefits and Impacts
Construction, maintenance, and operating costs must be weighed against the benefits and other impacts of the project. These may take the following forms and may be measured in the following ways.
In addition to examining total impacts it is also important to examine the distribution of impacts (for example, who benefits and who is negatively impacted.) Assuring an equitable distribution of benefits may be important from a local or national policy standpoint. Geographic equity is one aspect, e.g., ensuring that all regions of a country benefit from road and highway investments, and that rural as well as urban areas benefit. Equity among social classes may also be important, e.g., it may be important to ensure that economic opportunities reach those for whom existing conditions are poor. Mechanisms for funding roads should also be fair in the sense that those who are financing the project are also those who are benefiting from the road improvements.
For additional guidance on evaluating and comparing the benefits and impacts of highway projects, see Item 8 in the "Selected References" section of this document.
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