What’s in the Black Box? Beimborn, Edward A. 1995. A Transportation Modeling Primer.Center for UrbanTransportation Studies, University of Wisconsin-Milwaukee: http://www.uwm.edu/Dept/CUTS/primer.htm (last accessed 11/14/04).
Travel Demand Modeling • First developed in the late 1950s • Helps make decision on future development of (urban) transport systems • Forecasts travel patterns 15-25 years ahead • An understanding of the modeling process and assumptions is essential to understanding transportation plans.
Development of Model Input What will our community look like in the future? • How many people? (population forecasts) • What will they do? (economic forecasts) • Where will they do it? (land use pattern)
Model Area • Includes OKI and Dayton (MVRPC) Regions • 1,608 zones in OKI Region • 817 zones in Dayton Region • 63 external stations in OKI Region • 43 external stations in Dayton Region
Input – Transportation Network • What changes to the transportation system do we want to evaluate? • No change, existing system plus committed projects (E+C) • E+C plus future alternatives
Representation of Transportation Network • Network consists of links and nodes • Includes current bus system; future year networks may include expansion to transit system • # of lanes, capacity and speed by link • Transit links for fixed route service; stops,park-n-rides, headway, vehicle size
McCabe, Frank. Modelling Transport: Theory and Practice. Dublin Transportation Office: http://www.icetact.tcd.ie/icetact/news/transport/mccabe.html (last accessed 11/14/04).
Structure of a 4-step Model What are the travel patterns in the future? • How many trips? (trip generation) • Where will the trips go? (trip distribution) • What modes will they use? (mode split) • What routes will they take? (traffic assignment)
Post Model • What will be the effects of this travel? (Impact Analysis) • Future volumes • VMT, vehicle hours of travel • Level-of-service • Transit ridership • Air pollution • Cost benefit analysis
Calibration • Models are calibrated to base year conditions. • Current OKI model base year is 2000. Model output is compared to over 3000 traffic counts. • The difference between total vehicle miles traveled (VMT) and observed VMT is less than 1%.
Model Limitations • Only considers factors and alternatives explicitly included in the equations. • Intersection delay not directly considered. • No bike or pedestrians (walking available as mode choice in some large CBD’s). • Not sensitive to access management improvements.
Future Model Advancements • Tour-based model • Assembles multiple trip legs into tours • Needs lots of household trip data and several large computers. • Traffic micro-simulation • Refine model output to analyze intersection and access improvements. • 2d and 3d • OKI is developing this capability.
Contact Information Andrew J. Reser, AICP OKI Regional Council of Governments firstname.lastname@example.org 513-621-6300 x146 www.oki.org