Base Year Data: Each TAZ is assigned an area type designation as CBD, Urban, Suburban or Rural based on population and employment density as determined from the 2000 Census.

Future Year Data: Revisions to the zonal area type classifications are made once the population and employment projections are completed for the future analysis year to reflect changing population and employment densities.

Model Calibration
OKI’s Travel Demand Model has been validated to observed traffic volumes for the model base year 2000. The modeling network encompasses the entire nonattainment area of Butler, Clermont, Hamilton and Warren Counties in Ohio, and the maintenance area Boone, Campbell and Kenton Counties in Kentucky. The modeling network also includes Greene, Miami and Montgomery counties in Ohio and Dearborn County, Indiana. The difference between estimated vehicle miles traveled (VMT) and 2000 observed VMT is less than 1%. A highway screenline analysis compares the screenline observed and simulated traffic volume discrepancies with the ODOT standard of maximum desirable deviation. The comparison shows that the model performs at a satisfactory level and all the errors were under the ODOT curve. Further information can be found in OKI’s 2004 report, “OKI/MVRPC Travel Demand Model Methodology/ Validation Report”. For the calibration, OKI used over 3866 traffic counts collected through 2004 by the Ohio Department of Transportation (ODOT), the Kentucky Transportation Cabinet, many county and local governments, transportation engineering consultants, and OKI. These traffic counts cover nearly 50% percent of the links in the OKI portion of the modeling network. The methodology provides consistency with past emission inventory and conformity analysis work performed by OKI.

Local Inputs and Post-Model Processing
OKI incorporates a variety of sources of local data to both improve and confirm the accuracy of VMT, as well as other travel-related parameters. Free flow speeds used on the highway and transit networks are based on travel time studies performed locally. The OKI post-processing program, IMPACT, uses the loaded highway network to generate VMT by hour, VMT by speed distribution and VMT by facility type. These tables are then included as input into MOBILE6.2. Two separate sets of VMT tables are generated: one for the four Ohio counties and a second for the three Kentucky counties. The VMT by hour tables utilize hourly traffic distribution and directional split factors for different roadway types as developed by OKI. The main source of the data was the permanent traffic counting stations located throughout the OKI region for the years of 1998-2002. This data was supplemented with data collected at coverage count stations (locations with counts taken on only one-two days). The stations were classified by area type: urban and rural, and functional classification: freeway, arterial and collector. Speeds representing various “loaded” conditions (with traffic volumes) are estimated using techniques from the 1997 Highway Capacity Manual. This permits the estimation of speeds as conditions vary from hour to hour on the different facility types throughout the region. The IMPACT program performs the appropriate summation by area and roadway type as well as regional totals. OKI has also developed seasonal conversion factors to adjust traffic volumes to summer conditions. The factors were derived from local data collected at permanent traffic counting stations during 1994-1997 utilizing the average daily traffic monthly conversion factors for June, July and August. Further information on OKI’s IMPACT program is documented in the report, “Travel Demand Model Summary Reporting and Impact Summary Reporting: OKI/MVRPC Travel Demand Model User’s Guide”, OKI 2003.