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this way. The primary advantage of this method is that the full- day activity patterns of the riders and other household members could be collected rather than information only on the transit trip in question. The onboard survey itself did not collect origin and destina- tion information in sufficient detail to be used to esti- mate mode choice models. METHOD OF CODING TRIPS AND TOURS Three traditional trip purposes were used: home- based work (HBW), home- based nonwork (HBNW), and non- home- based (NHB). These were coded on the basis of a lookup table of the 517 possible combinations of pro- duction place, production activity, attraction place, and attraction activity. The data were then coded into a tour format. Several codes were developed to support the most common approaches to tour- based modeling: ⢠Tour code: Trips in the same tour must be given a common tour identification (ID) number; ⢠Tour mode: The primary travel model for each tour must be designated; and ⢠Primary destination: One of the stops on each tour must be designated as primary. The method described here builds on the method out- lined in the Integrated Regional Model Final Report (2), which in turn builds on the work of previous tour- based modeling projects in San Francisco, California (3, 4); Portland, Oregon (5, 6); New York (7); Columbus, Ohio; (8) and Atlanta, Georgia (9). First, DRCOG developed a program to group trips into tours. Figure 1 illustrates an example of an individ- ualâs all- day activity pattern. A tour is a sequence of trips starting and ending at home, defining a single round trip. A subtour is a sequence of trips starting and ending at work, defining a single round trip. The example below includes three tours, one of which is a subtour. Trips 1, 4, and 5 compose Tour 1, Trips 2 and 3 compose Tour 2, and Trips 6 and 7 compose Tour 3. Because of the sub- tour, the trips in Tour 1 are not adjacent in time. To code the tours, the program passes forward through each trip, incrementing the tour ID whenever the traveler departs home. For each trip, it also keeps track of when the traveler last departed home and last departed work. For example, on Trip 5, the traveler last departed home on Trip 1 and last departed work on Trip 4. Next, the program passes in reverse through the trips, flagging any in which the traveler departed work more recently than he or she departed home. In this pass, if a traveler arrives at work and has departed work more recently than departing home, the trip is part of a sub- tour. The previous trip is also part of the subtour until the trip that actually departs from work is reached. Having flagged the subtours, the program once more passes forward through the trips, incrementing the ID of the subtour and of all subsequent tours. Most standard household trip surveys contain all the information needed to perform these steps. The primary mode of each tour is assigned by setting a priority to the mode of each trip, in the following order: 1, school bus; 2, kiss and ride; 3, park and ride; 4, walk to transit; 5, drive alone; 6, shared ride 2; 7, shared ride 3+; 8, bicycle; 9, walk; and 10, other. For example, if any trip on the tour is on a school bus, then the pri- mary mode of the entire tour is labeled school bus. It is not necessary that all trips in a tour have the same mode. For example, drivers switch between drive- alone and shared- ride modes when they pick up or drop off a passenger. Finally, for each tour, one place is designated as the primary destination. The primary destination is impor- tant because standard tour- based model structures assume that the activity at that destination controls the behavior of the tour and that the other stops are sched- uled around it. For example, if a traveler goes to work and stops for coffee on the way to work, the work activ- ity is far more likely than the coffee stop to dominate that personâs decisions about schedule, destination, and mode. The primary destination is set such that it is never home for any tour, and it is never the workplace for work- based subtours. However, it is possible to have work- based subtours for which the activity at the pri- mary destination is work, such as when someone visits a print shop or another companyâs office. In general, the place type, activity, and stop duration of each stop in a tour are the variables on which the des- ignation is based. A variety of methods may be used to designate the primary destination, from assuming that one of these variables has sole priority to developing a two- or three- dimensional weighting table (for example, one that assigns higher scores as duration increases for any given stop activity and then selecting the highest- scoring stop from the table). DRCOG has adopted a sim- ple decision tree structure, as shown in Figure 2. 50 INNOVATIONS IN TRAVEL DEMAND MODELING, VOLUME 2 Home Work Eat Meal Social Shop 7 6 5 4 1 2 3 FIGURE 1 Tour pattern illustration.