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is determined both by the duration of the activities and by the travel times to and from them. See Vovsha and Bradley (1). STATUS OF THE TIME- OF- DAY MODEL VALIDATION In the development of the MORPC TOD model, a dis- aggregate validation was achieved using the Home Inter- view Survey (HIS) data records. The MORPC validation report shows the results for the TOD model versus the observed values from the HIS, which, as expected, match. The TOD model, however, has not yet been fully validated against external data. MORPC does not have a sufficient number of traffic counts by peak hour or peak period to validate either the hour- grained TOD model or the period- level traffic assignments. To date, only the 24-h traffic and transit assignments have been validated (with respect to counts) and used for official planning purposes. The hour- level detail in the MORPC microsimulation results is aggregated to four general time periods (3-h a.m. and p.m. peaks, midday, and nightâearly morning) for highway and transit network loading. The hourly detail, however, is available in the final simulated tour- record- level disaggregate output. TIME- OF- DAY COMPARISON BETWEEN THE TIME- OF- DAY MODEL AND TRAFFIC COUNTS The Ohio Department of Transportation (ODOT) col- lects traffic monitoring data for Interstate, U.S., and state routes in the state of Ohio. Traffic monitoring data include vehicle volume, vehicle classification, and weigh- in- motion. Data are collected using manual, portable (road tube), and permanent automatic traffic recorders and intelligent transportation systems methods. Traffic count data are published by hour and vehicle type by functional class on a statewide basis (12). Table 1 shows the percent of half tours (departures and arrivals) and trips from the model and the percent of passenger vehicle traffic by hour of day for the base year 2000. As noted earlier, the model schedules tours between 5:00 a.m. and 11:00 p.m. Therefore, those hours account for traffic between midnight and 5:00 a.m., and are not directly comparable with the traffic count data. The traffic data by functional class are accu- mulated on a statewide basis; as such, the summary tables may not be as representative as data solely from the Columbus region. To calculate the average, the share by functional class was weighted by vehicle- miles- traveled share, as reported in the Highway Performance Monitoring System. Although number of tours or trips cannot be com- pared directly with traffic counts, several observations can be garnered. As seen from Table 1, the model is showing more tours starting or concluding in the a.m. peak hour and period than the p.m. peak hour and period. This can be partly explained by the model simu- lating an average weekday, as opposed to an average day. Furthermore, because both the HIS and the model show that people are more likely to make a stop on the inbound half of the tour, the trips are more balanced to the p.m. peak than the half tours. However, part of the apparent underestimation may be explained from the underreporting of nonmandatory tours in the HIS. While the model has been calibrated to take the underreporting into account, it is possible that some tours are still being missed. 162 INNOVATIONS IN TRAVEL DEMAND MODELING, VOLUME 2 TABLE 1 Percent of Tours, Trips, and Passenger Vehicle Traffic by Hour of Day, Base Year 2000 Traffic Counts by Functional Class MORPC Model (%) Total Urban Areas Statewide (%) Hour Half Tours Trips Average 11 12 14 16 17 5 2.1 1.9 1.8 1.9 2.4 1.7 1.6 1.4 6 2.7 2.6 4.6 5.2 5.5 3.9 3.8 3.7 7 8.1 7.7 6.9 7.7 7.2 6.0 6.0 5.9 8 9.0 8.5 5.6 6.1 5.6 5.2 5.2 5.2 9 5.8 5.5 4.7 4.8 4.5 4.8 4.6 4.6 10 4.4 4.4 4.7 4.4 4.8 5.1 4.8 4.8 11 4.3 4.4 5.3 4.8 5.1 5.9 5.8 5.8 12 4.6 4.6 5.7 5.3 5.3 6.2 6.2 6.3 13 5.3 5.4 5.8 5.7 5.4 6.0 5.9 6.0 14 5.3 5.2 6.4 6.4 6.1 6.5 6.5 6.7 15 6.4 6.1 7.6 7.7 7.5 7.5 7.6 7.9 16 7.5 7.4 8.1 8.2 8.2 7.8 8.1 8.2 17 7.0 7.3 8.2 8.3 8.3 7.9 8.2 8.3 18 6.7 7.1 6.2 6.1 6.0 6.2 6.5 6.5 19 5.5 5.7 4.6 4.2 4.3 4.9 5.1 5.1 20 4.4 4.5 3.8 3.5 3.6 4.1 4.3 4.3 21 4.5 4.7 3.2 3.0 3.1 3.4 3.5 3.3 22 3.2 3.4 2.3 2.2 2.4 2.3 2.4 2.3 23 3.4 3.7 1.6 1.5 1.8 1.6 1.5 1.5 Total 100.0 100.0 97.3 97.2 97.1 97.1 97.6 97.8