Travel Demand Model - OKI

OKI/MVRPC Travel Demand Model – Version 6.02.6 Model Calibration Refinements2.6.1 K Factor Estimation(a) Within the OKI Council RegionThe initial estimated trip distribution was validated on a county-to-county basis against OKIhousehold survey data. On the basis of this comparison a small set of K-factors were calculatedand applied to the model, primarily to correct the over-estimation of trips between NorthernKentucky and Ohio. This kind of overestimation is not unusual, given that the two regions areconnected only by a small number of bridges. It was also found that a correction was necessaryto better estimate Cincinnati CBD bound trips. Tables 2.3 to 2.8 show the observed andestimated OKI county-to-county trip tables for HBW, HBO and NHB trip purposes, after theapplication of K-factors. The final estimated K-factors are shown in Table 2.9. The K-factordistricts are shown in Table 2.10.(b) Between the OKI and MVRPC RegionsAs mentioned in the Introduction, the calibration of the OKI/MVRPC friction factors was basedentirely on trip distribution data from the OKI region. While there is no geocoded observed tripdata for the MVRPC region, the ODOT cordon survey allows validation of the distribution of tripsbetween OKI, Montgomery and Greene counties, and Miami County.The ODOT cordon data are limited in that only two trip purposes were recorded, work and nonwork,and also in that it is not known whether trips are home-based or non-home based 1 . Forthese reasons, the inter-regional K factors were calculated on the basis of total trips (i.e., not bytrip purpose). According to the ODOT cordon survey, there were approximately 94,000 personvehicle trips crossing the cordon between OKI and MVRPC. K-factors for the inter-regional ODpairs were estimated by trial-and-error with the objective of achieving approximately the ODOTtarget total. An adjustment by trip purpose was made to consider the trip estimate sensitivity tothe K-factor value. The final estimated K-factors are shown in Table 2.19. The K-factor districtsare shown Table 2.10.2.6.2 Bridge PenaltiesAs part of the highway assignment validation phase, it was found that, even with the use ofNorthern Kentucky to Ohio K-factors, the model still overestimated trips between these tworegions. For this reason, the bridge travel time penalties used in Model v54 were added to theskims derived from the highway network. The calibration of the gravity models and mode choicemodels was adjusted as a result of the updated skims. The results discussed in this reportalready reflect these adjustments.1 While the ODOT cordon survey questionnaire form includes a question requesting whether the trip startedor ended at home, this information was not included in the cordon survey data files provided to PB for thisstudy. The data items available for this study are listed in Figure 10 of the ODOT Cordon Line OD SurveyData Technical Memoranda.Trip Distribution - Gravity Model Calibration 10