Dealing with Uncertainty in Travel Demand Forecasting

Sources of error

When forecasting for the medium to long term we need to be clear in acknowledging that we are dealing with an uncertain future. There are a number of factors which may contribute to errors and uncertainty in forecasts. Sources of uncertainty when forecasting travel demand include:

Demographic and socioeconomic input data: employment and population market segments; economic activity: impacts on drivers for freight and passenger demand.

Assumptions about physical networks (base year and future projects): observed counts may affect model calibration and validation; road and public transport network assumptions.

Values of travel time (VTT): strategic transport models use an imputed VTT for each main trip purpose. VTT are usually estimated from the coefficients of mode choice models.

Time of day effects: factors are usually used for different time periods, (peak, daily, weekly, monthly, and annually), based on historical data. Such factors will not deal with peak spreading or mixes in the traffic composition. Methods to model time-of-day choice explicitly are beginning be implemented in practice.

Optimism bias: Use should be made of strategic transport models to investigate the impact of proponent optimism bias on overall results. Patronage optimism bias should be examined using sensitivity testing.

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Traffic Incident Response Practices in Europe

The U.S. Federal Highway Administration released a report that includes recommendations to improve traffic incident response in the United States.

The recommendations are based on an April 2005 scanning tour on traffic incident response practices, procedures, and technologies of England, Germany, the Netherlands, and Sweden that assessed and evaluated various practices for responding to traffic incidents.

The recommendations are organised under the three primary themes of programs and institutions, tactical and on-scene management, and communications and technology.

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Best Practices for Traffic Incident Management in Florida

Florida Department of Transportation released a report in 2005 that examines traffic incident management programs, procedures, and techniques from throughout the US and within Florida; summarises lessons learned and best practices; identifies suitable performance measures for incident management programs; and recommends overall program improvements for application in Florida. The report documents the best practices currently … Read more

Quick Clearance Toolkit Website

The I-95 Corridor Coalition has developed a Quick Clearance Toolkit website that includes links to material and videos designed to help jurisdictions initiate or improve quick clearance programs. The material includes a roadmap for developing a traffic incident management program designed to help provide policy makers and practitioners in traffic incident management with ready-to-use tools … Read more

Tabletop Exercise Instructions for Planned Events and Emergencies

The US Federal Highway Administration has released a guide designed to help in conducting tabletop exercises to test the effectiveness of transportation management plans associated with planned special events. The guide may also be helpful in the management of unplanned incidents including traffic incidents and responses to emergencies.

When planned special events are held, they generally increase traffic demands in or near the location of the event. In order to address this influx of traffic, transportation management plans are developed with the intent of minimising the effect the event has on the transportation system.

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US Report identifies travel demand modelling shortcomings

The US Transportation Research Board has recently conducted a major study into the state-of-practice of travel demand forecasting theory and application in that country.

TRB Special Report 288, Metropolitan Travel Forecasting: Current Practice and Future Direction, examines metropolitan travel forecasting models that provide public officials with information to inform decisions on major transportation system investments and policies.

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Traffic Incident Management: Best Practice

The Austroads Improving Traffic Incident Management project involves a review of traffic incident management in major urban regions across Australia and New Zealand. The fifth and final report released in July 2007 provides a brief overview of all aspects of traffic incident management, including planning, institutional issues, evaluation and performance review and capability development, as … Read more

Active Traffic Management in Europe

The combination of continued travel growth and budget constraints makes it difficult for transportation agencies to provide sufficient roadway capacity in major metropolitan areas.

The US Federal Highway Administration (FHWA), American Association of State Highway and Transportation Officials, and National Cooperative Highway Research Program sponsored a scanning study in July 2007 to examine congestion management programs and policies in Europe.

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Microsimulation as a Planning, Operations and Training Aid for Incident Management

The methodology for this study includes a literature review and a modelling case study of the West Gate Freeway in Melbourne. A microsimulation model was set up using AIMSUN NG for the study area. It is concluded that significant resources are required in setting up a microsimulation model for incident analysis. Once set up and … Read more

Improving Traffic Incident Management: Evaluation Framework

The third report of Austroads Project Improving Traffic Incident Management published in January 2007 provides an evaluation framework to assess priorities for new alternatives in traffic incident management (TIM). It involves a literature review of relevant evaluation approaches followed by application to three case studies.It was found that benefit costs analysis (BCA) provides for a … Read more