Transportation Model Update Report
o Measure economic effectiveness and economic impacts of project decision making; o Prepare for possible new air quality conformity standards; o Design an easier tool to use and increase staff training on the model.
Model Update Activities
Purpose of Model Update The purpose of the transportation demand model improvement and update is to support regional transportation planning activities leading to the development of the 2045 Long Range Transportation Plan (LRTP). The purpose of a truly multi‐modal transportation plan is to establish physical and cultural environments that support and encourage safe, comfortable and convenient travel by a variety of modes. The technical modeling and performance measurements procedures to be used in the transportation planning process should be designed to meet these needs. The Genesee County Travel Demand Model is a representation of travel patterns of the major roads in the county. The model uses population
and employment projections to project where people may be traveling on the road network in the future. The model was developed through a cooperative effort consisting of GCMPC staff, Michigan Department of Transportation (MDOT), the Model Development Committee and the modeling consultants from The Corradino Group. The model is used to determine the road network capacity deficiencies, to develop the list of capacity improvement projects for the LRTP, to test alternative projects to alleviate congestion and for air quality conformity analysis.
What were the goals of the update? o Update to a new 2014 Base Year and develop model scenarios out to 2045; o Improve the model capabilities;
The approved model years for this update included a new calibrated base year of 2014 with future years of 2020, 2025, 2035 and 2045. The Genesee County 2045 Population Projections were used to update the population, households, and persons per household attribute fields in the traffic analysis zones. The 2014 base highway and transit network geographical database were updated, and both use a master network which keeps all future network scenarios in one file. The speed and capacity calculators were also updated to the most recent methodologies of Highway Capacity Manual 2010 (HCM2010) which is used to assess the traffic and environmental effects of highway projects. The Genesee travel demand model uses a four‐ step modeling process with a travel time feedback loop. The four steps are trip generation, trip distribution, mode choice, and traffic assignment. The trip generation model was updated and the “MI Travel Counts” data was used for calibration. A gravity model with friction factors was used for trip distribution. A nested logit model was used for the mode choice model. The model divides the person trips into trips of five modes: car driver alone, car share ride, transit (bus), and nonmotorized (walk/bike). For traffic assignment,
the Genesee County model uses a time‐of‐day modeling procedure in which auto and transit assignments are made for each of the four periods which are summed to produce daily assignments. The time of day model includes an AM Peak, Midday, PM Peak and Night time periods and the MI Travel Counts dataset for all Transportation Management Area (TMA) trips was used to calculate a frequency distribution by departure hour for each trip purpose. Key Elements of the GCMPC Network: Number of Links: 4,310 Number of Nodes: 2,930 Number of Centroid Connectors: 1,452 Number of Traffic Analysis Zones: 639 Number of External Zones: 37
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