Project
description
IMR is reviewing the relatively large body of literature on
error and uncertainty in urban models to identify a range of plausible errors
for both project level and regional modeling analyses, the relative magnitude
of different sources of model errors, and the potential bias introduced by
models that do not represent certain theoretical relationships.
The range of plausible errors in transportation project and
policy studies is identified based on three types of studies: (1) forecast
versus actual project performance; (2) model validation tests; and (3) model
sensitivity analyses. Each study type has its strengths and weaknesses, but,
cumulatively, these results begin to delineate reasonable confidence bounds for
models typically used in transportation, land use, and air quality planning.
By examining the literature, researchers are also gaining
insight into the relative magnitude of various sources of model error. Additionally, the literature review addresses
the ability of current models to represent phenomena such as induced travel and
the degree of possible biases in the evaluation of alternative scenarios when a
model does not represent induced travel effects. The term, induced travel,
generally refers to the observed increase in travel that occurs as a result of some
economic or convenience factor or factors that encourage travel. When gas
prices go down, some argue, people drive more. When a highway is widened or a
new highway is built, the observed increase in traffic soon thereafter is an
example of induced travel.