MPO Policy and Procedures Manual - Indianapolis Metropolitan ...

vehicle hours of travel (VHT). The model area encompasses all portions of the nine-county
region of Central Indiana, including the counties of Boone, Hamilton, Hancock, Hendricks,
Johnson, Madison, Marion, Morgan, and Shelby.
The parameters of the travel model are estimated with information available from household
surveys, the Census, and other sources. Estimated parameters are applied to population and
employment estimates, resulting in regional trip totals broken out by trip type – work, school,
shopping, etc. The model is calibrated such that the network flows match to measured vehicle
counts at representative locations. The validation of the model ensures that the model provides
results consistent with current thinking on traffic flows and speeds, trip choice, and modal
choice.
The travel model has many uses. First, it provides us with an assessment of the current state of
the regional transportation network. Traffic counts and speed studies inform the model
development, but in and of themselves are too geographically limited to provide a broad
appraisal. Second, by varying the state of the network in terms of capacity, location or
operations, we can assess the efficacy of various transportation policies. Third, by varying the
population and employment inputs to match an expected future state, we can forecast the state
of the traffic system, subject to the limitations of the population and employment forecasts.
Finally, the travel model outputs can be “post-processed” to address a variety of policy
questions (e.g., economic impacts or air quality benefits/costs).
The model is based on theories and assumptions that are valid for regional travel movement.
Subregional results, therefore, should be viewed with caution. The smaller the area, the greater
the probability of forecasting error, particularly when queries focus on a specific network facility.
For specific network facilities, if a traffic count is available, a time-correction of the traffic count is
preferable to a model output for that facility. If a traffic count for the facility is not available, then
a model output may be issued if caution in applicability is observed.
Travel Model Requests and Procedures
Community stakeholders may request that MPO staff run the model to test various scenarios.
Generally, the MPO will try to accommodate these wishes, but requesters needs to be aware
that significant staff and computer time is utilized in running the model, and that the MPO
reserves the right to re-scope, or even reject requests based upon resource availability. This is
staff time-intensive requesters should expect a turnaround time of no less than eight weeks.
External Use of the Travel Model
Consultants and other external parties are generally permitted to directly run the travel model,
with the following caveats, which constitute requirements for use of the model. Any violation of
these caveats may result in the suspension of the stakeholder’s permission to use the model:
• The travel model is the property of the MPO. The MPO needs to be properly credited in
any report;
• Final model results for major investment studies, environmental impact statements; et
cetera must be verified by the MPO. This verification requires the submittal of the
networks and, if applicable, zones to the MPO for an independent run of the model. In its
review and verification, the MPO reserves the right to alter any network or zonal coding
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