Norman W. Garrick

Transportation ForecastingWhat is it?

Transportation Forecasting is used to estimate the number of travelers or vehicles that will use a given transportation facility in the future

The conventional approach to transportation forecasting is based on what is commonly know as the ‘four step model’

Norman W. Garrick

Transportation ForecastingWhat is it used for?

Transportation forecasting models have often been used in a ‘predict and provide’ mode to determine the highway capacity needed in response to predicted growth in traffic volumes.

Often, in this case, the full impact of changes in land use is not properly taken into account and the resulting induced traffic is over looked.

Norman W. Garrick

Transportation ForecastingScenario Planning

If transportation forecasting models are adjusted to properly account for the impact of changes in land use patterns they are useful for evaluating the implications of different transportation choices. In other words, they can be used for so called ‘scenario planning’.

Norman W. Garrick

Transportation ForecastingScenario Planning Example

For example, transportation forecasting models can be used to answer the following question

What will a region look like if we develop1. Based mostly on highways with no land use

control2. Based mostly on transit system with land use

control that favor transit oriented development

Norman W. Garrick

Traffic Congestion in Chicagoland 1996

Thanks to Lucy Gibson, Smart Mobility

Norman W. Garrick

Traffic Congestion in Chicagoland 2020 Scenario 1 (Business as Usual)

Thanks to Lucy Gibson, Smart Mobility

Scenario 1Business as usual = Predict and Provide

More highwaysLittle investment in Transit

More sprawlMore decay in cities

Norman W. Garrick

Traffic Congestion in Chicagoland 2020 Scenario 2 (Transit Oriented

Planning)

Thanks to Lucy Gibson, Smart Mobility

Scenario 2Transit Oriented Planning

Less highwaysMore Transit

Develop in CentersRevitalize Cities

Norman W. Garrick

Transportation ForecastingOther Questions

Transportation forecasting models, with proper accounting for land use impacts, can be used to answer specific questions such as

• What is the effect of congestion charging?• What is the effect of parking control and

transportation demand management?• What is the effect of more concentrated

development?

Norman W. Garrick

The Four Step Model

• Trip GenerationEstimates the number of trips from given origins and destinations

• Trip DistributionDetermines the destination for each trip from a given origin

• Mode ChoiceDetermines the mode choice for each trip

• Route AssignmentDetermines the specific route for each trip