ADOT has a long history of travel modeling in the Arizona. In 1985 ADOT developed the travel demand models for Maricopa Association of Governments (MAG) and Pima Association of Governments (PAG) MPO's. Responsibility for these models was transferred to the MPO's in 1991. More recently, with the development of the 1st generation statewide model ADOT has once again jumped into the model development world. In 2008, ADOT along with MAG and PAG formed a model advisory committee to foster coordination and development across travel models and across jurisdictions.
The first generation Arizona Statewide Travel Demand Model (AZTDM1) was developed in 2009 as a three-step trip based model. AZTDM1 had a coarse network and zone structure (zone structure based on Census tracts) and used rates borrowed from Indiana and the Quick Response Freight Manual (QRFM).
The model provided estimates of general statewide performance of alternative system improvement strategies. It was used during the visioning activities of the Building a Quality Arizona Framework Study. Due to the aggregate structure of the first generation model, AZTDM1 was determined to have limited suitability for both transportation planning and to answering many of the policy questions anticipated in current statewide transportation system planning and development activities.
ADOT is currently using the second generation of the statewide model, AZTDM2. Development of AZTDM2 was initiated in March 2010 and completed in May 2011. Development focused on increasing the input data detail and on implementing improved personal and freight travel demand model components.
Zonal detail increased approximately six-fold from the first generation model, primarily in the urban areas where AZTDM2 uses a one‐to‐one correspondence with the zone structure from the MPO models and in emerging areas outside MPO boundaries. The highway network also had enhanced detail, including a direct import of the MPO networks in the urban areas. AZTDM2 included an extended external zone system (and corresponding highway network) covering North America allowing the model to capture important long distance person and truck travel as well as the visitor market to Arizona.
The AZTDM2's personal travel demand model component was calibrated using the 2009 National Household Travel Survey (NHTS) data as the primary source of travel behavior information. The calibration/validation database consisted of approximately 7,000 household samples, which includes an additional 4,286 samples purchased by MAG and 2,285 by PAG.
The freight and goods movement component of AZTDM2 was based on available data from sources such as the FHWA Freight Analysis Framework (FAF3) and the Bureau of Transportation Statistics (BTS) databases.
In July 2010, ADOT initiated the development of the third generation model, AZTDM3. The initial focus of this work will be on transitioning from a 3-step to a 4-step model. This will involve incorporating a person-mode choice model component and using an abstraction of local transit services. Non-local services (i.e., fixed-guideway and other line haul transit services) will still be explicitly coded. AZTDM3 will be capable of providing estimates of transit use for major system and service improvements for multimodal planning studies.
ADOT has recently acquired the Global Insight Transearch database which will provide commodity flow data at the TAZ-level for Arizona. This will enable further refinements to the existing truck freight modeling components and the potential addition of a rail freight component to the model. ADOT also plans to conduct in the near future a cordon count and classification study with a view towards possibly collecting origin-destination information for vehicles entering, leaving, and passing through Arizona.
Other model improvements ADOT plans to include in AZTDM3 are a stratified trip distribution model and feedback interactions with other model components (vehicle availability, trip generation, trip distribution and network assignment).
Beyond the current model development phase, ADOT is planning further refinements to the statewide model. These include: a population synthesis model, an activity-based model, a dynamic traffic assignment model, an integrated land use/transportation model and an economic model. These model improvements are considered to be part of the fourth generation model, or AZTDM4.
The historical context of ADOT's statewide travel model and the future development plans are summarized in the following chart.
