Building the Case: Improving the Credibility and Reliability of Travel Demand Models to Meet Changing Needs (original) (raw)
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Role of travel demand models in appraisal and policy-making
Impact Assessment and Project Appraisal, 1998
The purpose of this paper is to examine the role of travel demand models in the appraisal and policy-making process. The travel demand modelling process is described, with particular emphasis on identifying where policy issues can be examined and possible weaknesses in the methodology. Then the historical development of the models is considered. This is a mixture of policy-making, public pressure, government response, and analytical development. It is shown how the national road-building programme is intimately linked with the process of forecasting the demand for road space. However, the forecasting procedure is pragmatic rather than theoretically sound, and not very accurate. Similar weaknesses are found at a local level. The paper is concluded by consideration of ways of improving the forecasting procedures.
The use of economics in urban travel demand modelling: A survey
Socio-Economic Planning Sciences, 1976
This paper attempts to survey the recent innovations in urban transport planning and in particular to demonstrate the increasing importance being attached to economic analysis in the travel forecasting procedures employed. The article begins by setting out traditional economic notions as they relate to travel, progresses to illustrate their practical limitations for planners and then considers the applied work which has been attempted in this field. The paper is critical of the traditional sequential forecasting procedures and attempts to present a balanced picture of the current state of explicit demand modelling which has a firmer foundation in economic theory.
Do planners get it right? The accuracy of travel demand forecasting in Norway
European Journal of Transport and Infrastructure Research
This paper deals with the accuracy of travel demand forecasts among Norwegian road projects. We use data collected from tolled roads and toll free roads. The results reveal that while traffic forecasts of tolled schemes are fairly accurate, traffic forecasts among toll free roads have a higher degree of inaccuracy and are generally underestimated. An explanation for the observed discrepancy between estimated and actual traffic among toll free roads is that road planners may have ignored the existence of induced traffic and that the standard national traffic growth rates used in the transport models has been too low. For tolled roads, an explanation for the higher degree of forecast accuracy is that planners over the years have been scrutinized to provide careful estimates. Our recommendation is that traffic forecasts provided by planners should constantly be subjected to scrutiny by independent consultants before being presented to the decision makers. Aspects that need to be specif...
Transportation Research Part A: Policy and Practice, vol. 39, no. 6, pp. 522-530, 2005
Project promoters, forecasters, and managers sometimes object to two things in measuring inaccuracy in travel demand forecasting: (1) using the forecast made at the time of making the decision to build as the basis for measuring inaccuracy and (2) using traffic during the first year of operations as the basis for measurement. This paper presents the case against both objections. First, if one is interested in learning whether decisions about building transport infrastructure are based on reliable information, then it is exactly the traffic forecasted at the time of making the decision to build that is of interest. Second, although ideally studies should take into account so-called demand “ramp up” over a period of years, the empirical evidence and practical considerations do not support this ideal requirement, at least not for large-N studies. Finally, the paper argues that large samples of inaccuracy in travel demand forecasts are likely to be conservatively biased, i.e., accuracy in travel demand forecasts estimated from such samples would likely be higher than accuracy in travel demand forecasts in the project population. This bias must be taken into account when interpreting the results from statistical analyses of inaccuracy in travel demand forecasting.
Transport Reviews, 2012
Since the passage of the Intermodal Surface Transportation Efficiency Act in 1991, a significant number of state highway agencies have started to develop and implement statewide travel demand models to meet policy and legislative development needs. Currently, however, a lack of up-to-date multimodal and inter-regional passenger travel data hampers analysts' ability to conduct quantitative assessments of long-distance travel infrastructure investment needs, at both the national and statewide levels. Despite these data limitations, but also largely shaped by them, long-distance travel modelling has become an increasingly popular topic in recent years. This paper reviews several methodologies for multimodal inter-regional travel demand estimation, drawing examples from both state-specific modelling within the USA and from fully national models being developed and applied in other parts of the world, notably in Europe.
Chapter 8 Travel Demand Forecasting & Modeling
The Travel Demand Forecasting and Modeling process for the Jackson MPO was developed in cooperation between the Region 2 Planning Commission (R2PC) and the Urban Travel Analysis unit within the MDOT. MDOT was the lead role in the development, calibration, validation, and application of the Travel Demand Forecast Model (TDFM or " model "). The Jackson MPO acted as the liaison among members of the public, local agencies, and the JACTS Technical Committee, the JACTS Policy Committee, and the Region 2 Planning Commission. R2PC and MDOT collaborated on the development schedule of the model, as well as dissemination and distribution of model input and output data for review, comment, and subsequent approval. Travel Demand Forecasting Models are used to identify and evaluate the capacity demands of a region's federal-aid road network. Identification of roadway capacity deficiencies and analysis of the system as a whole, for the current year through and up to the Horizon Year of the plan, is vital in the development of the plan. A thorough review of the capacity demands of the roadway system is conducted at the regional level and then evaluated with the goals associated with the plan, along with anticipated financial outlooks. The assessments, priorities, and overall strategies included in the plan are used to guide decision-makers in developing the Transportation Improvement Plan (TIP), which is used to program current and upcoming transportation projects, as well as to identify investments of the projects on the federal-aid road network within the MPO. As economic conditions, transportation system trends, financial outlooks, and land use environments change, it is important that the plan be updated to reflect and account for these changes. The plan, following federal laws and regulations, is reevaluated and/or updated every five years to reassess the travel demands on the federal-aid transportation system. Along with the plan update, the TDFM is also redeveloped or updated to include the changes associated with the new plan. Socioeconomic trends and forecasts are also reexamined, which alters travel behavior and demand on the federal-aid road network, and may potentially change strategies of the Jackson MPO. The TDFM is a valuable tool used to identify and analyze the capacity demand of the Jackson MPO transportation system. Model results are useful in aiding the decision-making process. The modeling process and resultant outputs are provided at a regional level and are not necessarily applicable to small areas. The identification and analysis of corridor capacity deficiencies and associated travel projections are intended to serve as the basis for forming decisions regarding system improvement, expansion, or for other roadway capacity changes.
Modelling Long-Term Impacts on Travel Demand
PROCEEDINGS OF THE AET EUROPEAN TRANSPORT CONFERENCE, HELD 10-12 SEPTEMBER, 2001, HOMERTON COLLEGE, CAMBRIDGE, UK - CD-ROM, 2001
"Tor Vergata" 1. INTRODUCTION That urban land use and transport are closely inter-linked is common wisdom among planners and the public. In facts, that the spatial separation of human activities creates the need for travel and goods transport is the underlying principle of transport analysis and forecasting. Following this principle, it is easily understandable that the suburbanisation of cities is connected with increasing spatial division of labour, and hence with ever increasing mobility. The analysis of the impacts of land-use on the transportation system is wellestablished as well as the modelling approaches (e.g. the traditional fourstages model); on the other hand, the reverse impact from transport to land use, is less well known. In order to evaluate long-term impacts on travel demand due to changes in transport supply, it is not possible to disregard the impacts on land-use and, indirectly, on travel demand. The problem of simulating such effects has been tackled by different modelling approaches, labelled in literature as "integrated land-use/transport models" (Wilson, 1997). In this paper the focus is on the impacts that transport supply has on the distribution of urban activity locations (e.g. residents, services, commerce, etc) and, consequentially, on travel demand (e.g. spatial distribution, modal split and so on). The analysis is carried on by means of models dealing with the complex interactions between transportation and urban activities. With respect to other models present in literature, what actually is pointed out in the proposed modelling approach, is the transport component. The latter is typically represented in terms of generalised transportation cost, while here it is explicitly represented by means of demand models and transportation networks. Individual choices of residential and activity location are simulated through Random Utility Theory. The interaction between different individuals (i.e. residents, firms, etc) is simulated through a static (or equilibrium) approach. The latter seems more suitable for practical applications since equilibrium models are easier to be calibrated and implemented, with respect to more complex dynamic modelling framework (Simmonds, 2000). In order to provide the context, a review of studies on the impact of transport on land-use is described in section 2. Section 3 and 4 deal with the adopted modelling framework and its applications to the urban area of Rome (Italy) in order to predict the land use and the travel demand long-term variations induced by changes in transport supply system. The results of such applications are discussed and compared with those carried out by means of traditional four-stages demand model calibrated on the same urban area. Conclusions and further research issue are dealt with in section 5.
Integrating Transportation and Economic Models
1999
This study explores how different asset management, traffic forecasting, performance, and economic models can be integrated to show the national economic implications of transportation funding and performance gaps under different scenarios. Asset management models have often been utilized to assess and forecast the condition and performance of current infrastructure. Travel demand models have been used to anticipate how traffic volumes are likely to develop over time depending on capacity improvements. User-cost models have been used for cost-benefit analysis and the management of trade-offs, and economic impact models have been used to characterize transportation choices in terms of earnings, output, and employment. This study explores how a sequence of these models when applied to a consistent data set with consistent assumptions can address the overall relationship between physical transportation system conditions and performance, traffic patterns, transportation costs, and economic impacts. The results point to a vertically integrated and economically defensible approach to needs-based planning with an understanding of the national economic significance of transportation investment choices.
The propagation of uncertainty through travel demand models: An exploratory analysis
The Annals of regional science, 2002
The future operations of transportation systems involve a lot of uncertaintyin both inputs and model parameters. This work investigates the stability of contemporary transport demand model outputs by quantifying the variability in model inputs, such as zonal socioeconomic data and trip generation rates, and simulating the propagation of their variation through a series of common demand models over a 25-zone network. The results suggest that uncertainty is likely to compound itselfrather than attenuateover a series of models. Mispredictions at early stages (e.g., trip generation) in multi-stage models appear to amplify across later stages. While this effect may be counteracted by equilibrium assignment of traffic flows across a network, predicted traffic flows are highly and positively correlated.
The Shortcomings of the Conventional Four Step Travel Demand Forecasting Process
Originating from 1960s, and improved in the decades to come, four-step travel demand forecasting process is the central column of transportation planning throughout the world. However, despite numerous improvements, this model suffers from a several serious drawbacks. In this paper, we present detailed shortcomings of each of the four steps, and the process in general. In addition, considering that the demand for improved transportation planning is greater than ever, we identify several recommendations for improvement.