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52 I N N O VAT I O N S I N T R AV E L D E M A N D M O D E L I N G , V O L U M E 2 TABLE 3 Comparison of Tour Purpose and Trip Purpose for Trips Trip Purpose HBW HBNW NHB Total Tour Expanded Row Expanded Row Expanded Row Expanded Row Purpose Trips (%) Trips (%) Trips (%) Trips (%) Work 1,497,387 50 495,971 16 1,012,793 34 3,006,151 100 School 180 0 1,017,667 77 299,596 23 1,317,443 100 Shopping 1,591 0 689,607 62 424,438 38 1,115,635 100 Socialrecreational 653 0 560,063 71 227,082 29 787,797 100 Drop off and pick up 248 0 528,673 85 90,260 15 619,180 100 Other 5,626 0 1,152,088 61 734,116 39 1,891,829 100 Total 1,505,685 17 4,444,067 51 2,788,283 32 8,738,035 100 potentially one of the biggest advantages of a tour-based codes to support the development of tour-based models. model. The place survey conducted by DRCOG was not notice- On average, each person in the Denver region makes ably more complex than a traditional trip survey, and 4.4 trips per day and 1.6 tours per day, for an average of our experience with the data suggests that it would also 2.7 trips per tour. Of all tours, 38% include three or be possible to develop tour codes by using a trip-based more trips, and 55% of trips are on tours with three or survey. These results suggest that many metropolitan more trips. These results show that a large fraction of planning organizations may already possess the data travel includes some trip chaining, and developing a they need to develop tour-based models. model that properly accounts for this phenomenon Finally, one specific lesson learned from DRCOG's could have a significant influence on the model's experience is that there is no substitute for a robust performance. onboard transit survey. DRCOG used a brief onboard Finally, notice the difference in mode shares between survey to recruit transit riders to participate in its home- trips and tours. These differences result from the priori- interview survey. While this transit oversample provided tization scheme used to define the primary mode of the extremely useful data, the sample size was too small to tour. The shared-ride mode was defined as a lower pri- provide a complete picture of the use of the transit sys- ority than the drive-alone mode, such that if any trip on tem, and a full onboard survey would provide a nice a driving tour is a drive-alone trip, the primary mode complement to the oversample. would be drive alone. Drive alone takes a higher prior- ity because it requires the exclusive use of a vehicle, and the tour coding of the modes correctly captures that the REFERENCES driver at some point needs use of a vehicle. Conversely, transit is a high priority in defining the primary tour 1. Lawton, K. Activity and Time Use Data for Activity-Based mode, and the transit mode share is 50% higher for Forecasting. Proc., Activity-Based Travel Forecasting Con- tours than for trips. This result indicates a substantial ference: Summary, Recommendations and Compendium of level of trip chaining on transit tours, in which travelers Papers, June 25, 1996, Texas Transportation Institute, may stop to shop at some point during their transit trip. Arlington, 1997. 2. PB Consult and Gallup Corporation. The Integrated Regional Model Project: Vision Phase Final Report. Den- CONCLUSIONS ver Regional Council of Governments, Denver, Colo., March 2005. In total, the survey data present a reasonable picture of 3. Bradley, M., M. Outwater, N. Jonnalagadda, and E. Ruiter. travel behavior and one that is both more interesting and Estimation of an Activity-Based Microsimulation Model more intuitive than traditional trip-based statistics. They for San Francisco. Presented at 80th Annual Meeting of the make plain the degree of trip chaining at which the trip- Transportation Research Board, Washington, D.C., 2001. based statistics hint and show primary destination 4. Jonnalagadda, N., J. Freedman, W. A. Davidson, and J. D. purpose statistics that make sense given most people's Hunt. Development of Microsimulation Activity-Based perception of their primary daily activities (work for older Model for San Francisco: Destination and Mode Choice adults and school for children and young adults). Models. In Transportation Research Record: Journal of the DRCOG's experience with the use of its home- Transportation Research Board, No. 1777, TRB, National interview survey in the development of tour codes Research Council, Washington, D.C., 2001, pp. 2535. strongly suggests that complex, advanced activity-based 5. Bradley, M. A., J. L. Bowman, Y. Shiftan, K. Lawton, and surveys are not necessary to develop reasonable tour M. E. Ben-Akiva. A System of Activity-Based Models for