GUIDELINES FOR SELECTING TRAVEL FORECASTING METHODS AND TECHNIQUES

Transcription

1 GUIDELINES FOR SELECTING TRAVEL FORECASTING METHODS AND TECHNIQUES Maren Outwater and Jeff Doyle, RSG, 55 Railroad Row, White River Junction, VT ABSTRACT There have been guidelines in the travel forecasting field to apply various methods, but these are guidelines to determine which method to apply for a given situation. This NCHRP project will evaluate planning programs and desired performance metrics, as well as requirements and constraints in determining the possible methods that could be applied. In addition, we provide an interactive software that allows changes to the requirements to produce a different set of methods for consideration. Methods are presented in the context of costs and benefits so that users can review the determinants of a particular method and weight the various requirements to ensure that the methods reflect an agency s priorities. The guidelines will package technical information with planning requirements to provide a bridge between a travel forecasting practitioner s needs, the transportation planner s expectations and the decision-maker s understanding at a transportation agency. OBJECTIVES AND MOTIVATIONS Travel forecasting practitioners must now answer complex planning and policy questions using travel forecasting models originally developed with a narrower objective 1. These original objectives focused on evaluating expansion of roadway facilities. Current travel forecasting models are used to evaluate pricing, environmental, economic, and growth policies as well as highway, transit, non-motorized, and freight alternatives; these evaluations include an expanding set of performance metrics to compare the benefits and costs of the alternatives. Examples of new performance metrics include the effects on the built environment, public health, and distribution of effects over different socioeconomic groups. Federal regulations and the need for funding are the primary drivers of travel forecasting model requirements 2. These regulations have led to travel model improvements in managing travel demand, connecting modes, reducing emissions, and evaluating equity. More recently, reductions in public funding have led to travel model improvements in evaluating economic development, pricing strategies, and comparing economic impacts. The goal of this study is to develop guidance on long-range planning travel forecasting tools that address policy questions, produce desired performance metrics and meet applicable regulations. The objectives to achieve this goal include: Evaluate capabilities and limitations in current methods and tools. 1 McNally, M. G. The Four Step Model. In Handbook of Transport Modeling, 2nd ed. (D. A. Hensher and K. J. Button, eds.), Pergamon, Irvine, CA, 2000, pp Johnston, R.A. The Urban Transportation Planning Process. In The Geography of Urban Transportation, 3rd ed. (S. Hanson and G. Giuliano, eds.), The Guilford Press, New York, NY, 2004, pp

2 Identify model improvements appropriate for the desired level of transportation analysis, weigh the cost to benefit, and make informed choices given scarce resources. Communicate strengths and limitations to decision-makers. The research will address major model updates, required by a transportation plan or program, as well as corridor or area-specific model improvements, required by a specific transportation project. The guidance will include multiple planning questions to support a transportation plan or program, since these often address multiple objectives. This research will produce two primary products. The first is a document with guidelines for selecting travel forecasting methods, including specific features. The second is a method selection software tool that contains the information from the guidelines document combined with the ability to trade off costs and benefits for individual methods and features. This tool will also allow users to include current methods (optionally) so that results are tailored to improvements on current methods. METHODOLOGY PART I PLANNING PROGRAMS AND PLANS In the first part, the user will identify the planning program or plan of interest to their agency or organization. These transportation-related policies, programs, plans, and/or investment projects will address one or more planning issues or questions in the following categories: Transportation; Land-Use; Environment; Economic; Equity; and Safety and Health. These categories do not limit the performance metrics or alternatives that can be tested, but identify the primary use of the results. For example, a LRTP is a planning program in the Transportation category, but this program will have environmental, land-use, economic, transportation, quality-of-life, and equity performance measures. PART II PLANNING CONTEXT In the second part, the user will provide details regarding the overall planning context of the program or plan for which they are seeking analytical method recommendations. The user will also provide additional details about the agency s planning area. The software tool will evaluate the context of the planning exercise or analysis using the three standard categories of the project management triangle, also known as the tripleconstraint model (Figure 1). The angles of the triangle represent the requirements and constraints on scope, schedule, and resources. Accurately and explicitly describing these constraints is required for high-quality transportation planning and is necessary in order for the software tool to provide guidance on appropriate methods for consideration. To help the user fully understand the planning context, the software tool will evaluate the requirements, analytical rigor, and sensitivities necessary to address the planning issue and question. The research team 2

3 envisions that the user will provide the software tool with schedule and resources (budget, staff expertise, data, and information technology); these inputs will then be compared by the software tool to a separate assessment of the schedule and resource needs. Table 1 presents the planning context categories and elements within each category, along with one sample question associated with each element. The research team envisions that the user will provide the software tool with schedule and resources (budget, staff expertise, data, and information technology); these inputs will then be compared by the software tool to a separate assessment of the schedule and resource needs. TABLE 1: ELEMENTS OF THE PLANNING CONTEXT CATEGORY ELEMENT QUESTION SCOPE Product Regulation Analytical Rigor Traveler Sensitivities Spatial Detail Temporal Detail What outcome is expected? Are there regulatory or other requirements? Is this a feasibility study, a planning study, or an investmentgrade analysis? What travelers are affected? What factors must the analysis be sensitive to? What is the desired level of spatial detail? What is the desired level of temporal detail? SCHEDULE Time How much time is available for the analysis? RESOURCES Budget Staff Expertise Data Information Technology How much budget is available for the analysis? Will staff need training or an external consultant to support the analysis? Are the data available or will they need to be collected? Is the hardware and software available or can it be purchased? PART III PERFORMANCE MEASURES In the third part, the user will choose performance measures of interest to the agency. The performance measures will be limited to and associated with the planning program and plan for which she or he is seeking analytical method recommendations. 3

4 Performance measures have increased considerably in the past 10 to 20 years, and there are now hundreds of different performance measures in use across the United States. Many performance measures are reported as part of a monitoring process; 3 4 not all of these are amenable to forecasting. Hence, the discussion is limited to those performance measures that would be or could be used in conjunction with forecasts from travel demand models. The guidance will include six major categories of transportation planning performance measures: 1. Passenger Transport Measures: Mode Shares, Traffic Measures, Transit Measures, Mobility, Congestion 2. Environmental Measures: Air Quality, Energy Consumption, Noise 3. Economic Measures: User Benefits, Revenues, Economic Development, Accessibility 4. Freight Transport Measures: Mobility, Traffic Measures, Congestion 5. Community Measures: Land-Use, Schools, Environmental Justice, Social Equity 6. Health and Safety Measures: Active Transportation, Safety The guidance will include all of the performance measures with example metrics. The list of performance measures available to the user in the software tool will depend on her or his accumulated responses in Parts I and II. For instance, a Safety performance measure is not likely to be of interest for a transit corridor study that is primarily seeking to evaluate ridership. Narrowly specifying the input elements will improve the accuracy and relevancy of the software tool. PART IV METHODS, REQUIREMENTS, AND PARAMETERS Figure 1 presents the list of methods that will be included in the guidance. These methods include passenger travel demand model components, other travel demand model methods, commercial vehicle travel demand model components, and assignment and simulation methods. The research team considered a wider range of methods during the development of the conceptual design. The guidance will include information on which method is appropriate for each program, planning context, and performance measure element. Some of the performance measures identified, such as the environmental or economic, may require additional analyses to produce. The software tool will note these methods are possible, with a reference to the additional type of impact analysis needed to produce them. The guidance will explain that method parameters can be estimated or transferred from another area employing the same method. The guidance will not describe how to estimate or transfer model parameters, but will state that estimation with local data sources will provide a more-customized set of results than transferring a model from another area. PART V COST AND BENEFIT TRADEOFFS The outcome of the guidance will be a menu of recommendations for methods. This is termed a menu of recommendations because several individual enhancements to methods may be possible within the budget or time available. The menu will contain a series of advantages or benefits and a set of disadvantages or costs for the user to consider. Multiple methods may be employed in sequence or parallel in some cases

5 The guidance document will produce information on these costs and benefits for each method. The software tool will allow the user to adjust the planning context element and performance measure inputs to achieve a different menu of recommendations; specifically, this process will redefine the requirements and constraints that the menu or recommendations are based on. 5

6 FIGURE 1: LIST OF METHODS BY CATEGORY Passenger Travel Demand Components Other Travel Demand Methods Commercial Vehicle Travel Demand Components Assignment and Simulation Aggregate Models Trip Production (Cross-Class) Trip Attraction (Regression) Trip Distribution (Gravity) Mode Choice (Fixed Factors ) Time of Day (Fixed Factors) Disaggregate Models Population Synthesis Daily Activity Patterns (Discrete Tour Frequency (Discrete Destination Choice (Discrete Mode Choice (Discrete Time of Day Choice (Discrete Parking Location Choice (Discrete Transit Pass (Discrete Ridership Forecasting - Direct Demand Travel Demand Management Pricing Evaluations and Toll Modeling Origin-Destination Matrix Estimation Pivot-Point Incremental Select Link/Zone Analysis Feedback/Convergence External Travel Models Special Market Models (University, Airports, Visitors) Aggregate Models Trip Production (Cross-Class) Trip Attraction (Regression) Trip Distribution (Gravity) Mode Choice (Fixed Factors ) Time of Day (Fixed Factors) Commodity Flow Models (Allocation) Disaggregate Models Firm Synthesis Supplier Selection Supply Chain Model (Discrete Mode and Path Choice (Discrete Vehicle Type and Tour Patterns (Discrete Tours and Stops (Discrete Stop Sequence and Duration (Discrete Static Equilibrium Volume-Delay Functions Stochastic Assignment Dynamic Traffic Assignment Dynamic Intersection Delays Route/Path Choice Model Traffic Microsimulation Integrated, Multi-resolution Diversion Analysis Ped/Bike Microsimulation 7

7 The following items detail the potential benefits of a specific method: Performance Measures Sensitivities Spatial Detail Temporal Detail The software tool will suggest a wide range of enhancements, with detailed costs of a specific method: Data Needs Staff Training and Expertise Years in Use Budget and Time The software tool will allow for adjustments to these costs to produce more or fewer methods that can be chosen with the resources available. The software tool will apply a score to each element, with higher scores for higher benefits and lower costs. For each method, the costs and benefits will be qualitatively evaluated. Costs and benefits are most useful when they are combined to produce a combined score. This requires quantifying the value of each cost or benefit via subjective weighting provided by the user. The user will determine if each benefit or cost has the same value or if some benefits or costs are valued more or less than others. For example, one agency may determine that budget and time are more important than performance measures or sensitivities and weight these accordingly. The qualitative scoring of each benefit and cost will be included in the guidance; the software tool can provide additional flexibility for the user to provide their own scoring of individual benefits and costs based on local knowledge. SOFTWARE TOOL Figure 2 presents the decision-engine entity relationship (ER) diagram for the software tool. This diagram comprises four parts: User Inputs. The User Inputs data tables store the dynamic data of individual travel forecasting practitioners using the software tool: their login credentials and the inputs that they provide to specify the specific planning needs for which the software tool will provide method selection options. Domain Taxonomy. The Domain Taxonomy data tables codify a pre-enumerated set of input parameters that allow the user to specify the problem domain for which the software tool will find solutions. Specifically, the set of Planning Programs and Plans the system recognizes, the characteristics of the Planning Context, and the various Performance Measures of interest to the user. The Domain Taxonomy is associated with Requirements and Constraints via a number of association tables that identify which specific detailed requirements and constraints are driven by the user s Program, Metrics, and Contexts. Methods and Parameters. The Methods and Parameters data tables codify the pre-enumerated characteristics of the solution set of Methods and their parameters. Requirements and Constraints. Requirements and Constraints are the common currency that permits linking of the user-specified problem domain to the set of Models chosen from the range of known methods to be proposed as possible solutions by the Method Selection Tool. 8

8 FIGURE 2: DECISION-ENGINE ER DIAGRAM 9

9 The list of potential methods that is an output of the decision-engine ER diagram is drawn from the same set of methods (Figure 1) as the UserScenario_Method that is input; the difference between the user method and the output method is that the user can optionally input the methods they are already using. IMPLICATIONS FOR TRAVEL MODELING This research will identify potential methods that are appropriate to answer planning questions. These include environment, transportation, quality-of-life, and equity questions. The guidebook and software tool are being developed to support travel forecasting practitioners at local, regional, and state agencies. Practitioners must keep up with new research and new methods, and policy and planning questions that cannot be answered with current methods. Selecting a travel forecasting method can impact schedules, budgets, and the quality of information used in decision-making for transportation investments. This research will support to travel forecasting practitioners in identifying the right-size tool. The outcome of the guidance for selecting travel forecasting methods will be a menu of possible options, with benefits and costs provided alongside each option. This design will make the menu of options relevant to a specific situation rather than presenting options that would not be possible within the time and money available to the user. In addition, the guidance will evaluate available resources for each program and recommend methods that can be implemented within these resources, with real-time adjustments for time and cost to evaluate methods that may require more or fewer resources. These guidelines will provide technical information for travel forecasting practitioners, information connecting the planning question to the methods for planners, and information on how to communicate the costs and benefits of the method to decision-makers. It will not be a technical How-to guide for practitioners, but will explain the reasons for choosing a certain method in language that travel forecasting practitioners, transportation planners, and transportation decision-makers can understand. This is intended to be used by travel forecasting practitioners at small, medium, and large regional and state agencies with varying degrees of technical understanding. STATEMENT OF INNOVATION This research offers a new tool to evaluate possible methods to address planning and policy questions. To the best of our knowledge, no tool of this type exists. Many travel forecasting practitioners are faced with new requirements and do not have time to research all the new methods to identify the best fit. In addition, agencies are faced with limited resources and would prefer to select a method that is appropriate for a given situation and set of resources. Elected officials and planners would like a means of understanding how these methods are chosen and why they are the best fit for their needs. The guidelines for selecting travel forecasting methods will provide travel forecasting practitioners, transportation planners, and decisionmakers with results that ensure the best method selection and the means to understand that selection.