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