Activity-Based Travel Demand Models: A Primer (2014) / Chapter Skim
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From page 71... ...
69 3 ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) 3.1 FOUNDATIONS 3.1.1 Demand Models and Supply Models Activity-based models are travel demand models.
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70 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER for each TAZ. These total trip productions and attractions are then disaggregated to O-D pairs in the trip distribution step.
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71 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) even parcel.
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72 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER The center and right diagrams in Figure 3.3 illustrate binary choices of whether to add an intermediate stop before or after the primary destination stop. Binary choice structures are efficient for predicting a "yes-no" type of response.
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73 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) shown in Figure 3.6, a person chooses to walk for the tour mode, leaving SOV and bike unavailable for the subsequent trip mode choices.
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74 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER maximum utility from a set of alternatives that are mutually exclusive, which we call the choice set. The observer does not know the true utilities; however, they may be inferred from the choices made.
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75 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) viously discussed, activity-based modeling systems make extensive use of such hierarchical or nested choices for more than just mode choice.
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76 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER based modeling systems. This is particularly true for nested choices and conditional choice relationships.
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77 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) 3.1.4.1 Activities Versus Trips Activity modeling does bear some resemblance to trip-based modeling in terms of generating activities, distributing them to locations and time periods, and choosing travel modes for them.
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78 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER since time-window availability criteria for the insertion of intermediate stops would be influenced by both activity duration and travel time to the primary destination. 3.1.4.4 Intermediate Stops on Tours There can be zero or more intermediate stops on the tour, which are stops made between the anchor location and the primary destination.
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79 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) 3.1.5.1 Mandatory, Maintenance, Discretionary, and At-Home Activities Activities are sometimes grouped into four general categories according to priority in the daily activity pattern schedule.
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80 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER work or school together are considered to be not engaged in a joint activity, the assumption being that they are engaging in independent work or school activities, even if in close proximity. In such cases, there is joint travel on the tour, but this is simply represented as a sharedride mode choice for both persons, not as an instance of joint activity participation.
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81 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) on her way home from work.
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82 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER other household members are an extra dimension that could be added to either a mandatory or nonmandatory day pattern. The exact number of mandatory, nonmandatory activities and tours, as well as joint activity participation would be determined in downstream models.
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83 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) model stream is referred to as "upward vertical integrity." Together the downward and upward vertical integrity built into activity-based model system designs help to ensure a high degree of internal consistency among space, time, and mode dimensions and to recognize their interdependence.
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84 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER Another aspect of aggregation bias is shown in Figure 3.16. The average impact of a change is not equal to the impact calculated at the average of the explanatory variables; this is symbolized by the tangents to the curve, representing slopes at each point.
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85 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) for each level of each variable, a step that can be inefficient if not intractable for large numbers of variables.
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86 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER choice models are consistently used in tripbased modeling systems. In a trip-based model, market segments are defined by trip purpose and household demographic groups, and the model predicts the probability of each mode for each O-D pair.
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87 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) than higher probability choices.
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88 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER condition. Convergence is important within the context of activity-based model systems because it provides confidence in the integrity of the model system and helps ensure that the model will be a useful analytic tool.
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89 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) Second, the activity-based model sample rates are often varied.
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90 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER of activity-based models systems, such as usual work and school location models, tour destination location models, and stop location models predict travelers' choices of locations. Spatial scale refers to the resolution or level of detail used to define the spatial units that collectively make up the region and that are used to characterize key model inputs, outputs, and sensitivities.
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91 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) model implementation can be used directly, or easily translated to, the activity-based model implementation.
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92 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER 3.2.2.1 Temporal Scale People experience time as a continuous phenomenon, with one moment seamlessly transitioning to the next; in activity-based model systems time is broken down into discrete intervals or time periods. As with the representation of space, the resolution used to define these time periods can vary from one activitybased model to another, and different temporal resolutions may be used even within the same activity-based model system.
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93 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) uling individual mandatory activities but before scheduling any individual maintenance or discretionary activities.
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94 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER sequentially, followed by these same choices being made at the trip level. There is no single correct placement of scheduling and time-ofday models in relation to other models.
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95 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) modeled area and that includes detailed information related to key explanatory variables.
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96 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER On the discretionary side, it can be useful to separate social visits as a separate activity purpose, as they often occur at residential locations, outside working hours. Outdoor recreation can be another useful activity category, as it can be tied to open space/parks/sport fields, and so forth, as attraction variables.
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97 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) mode choice models may contain more detail, such as transit submodes or tolling alternatives.
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98 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER hierarchy makes it impossible to use a direct measure because it depends on a yet- unmodeled outcome. This would be the case, for example, for travel time in a destination-choice model that is higher in the hierarchy than mode and/ or time-of-day choice, since in order to measure travel time directly it is necessary to know the mode and time of day.
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99 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) gion, while other measures such as buffer-based measures can be better at measuring very local accessibility over short distances.
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100 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER 3.3 COMPONENTS This section introduces the major types of components included in most activity-based model systems. The various types of components are then described in greater detail in the following subsections.
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101 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) model components determines which tours will be simulated in the "Tour & Trip" details components.
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102 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER use models, or other tools. It is common that agencies may have only limited or no forecast information on some of the marginal controls included in the population synthesis.
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103 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) bution.
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104 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER including the longer-term and mobility models (see Table 3.5)
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105 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) attractiveness of traveling between home and a potential work location across all available modes of travel.
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106 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER variety of activities can be reached without an automobile tend to own fewer automobiles, all else equal. The automobile and nonautomobile accessibility to the usual work locations of any workers in the household is also a key variable, and that is a key reason for predicting automobile ownership conditional on the usual work and school locations.
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107 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) comes zero.
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108 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER longer-term and mobility models. In the " Basic Activity-Based Model Structure" column at the left, the "Tour & Trip Details" from Figure 3.19 are shown as split into a number of different subcomponents.
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109 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) to the activity at the primary destination of the tour.
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110 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER of observed multioccupant vehicle tours (ridesharing) as well.
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111 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) • Four, five, or six broad time periods of the day (e.g., early, a.m.
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112 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER model but using discrete time. So, instead of simply using alternative-specific constants for each time period, one can model factors that tend to shift departure times earlier or later, or shift activity durations shorter or longer, using continuous variables in the model specification periods (Vovsha et al.
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113 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) two tour destinations are added in the result is that the person leaves home at 7:30 a.m.
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114 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER that may be most important in actual travel choices. The main variables to include in models of tour primary destination choice are the same as listed earlier in Table 3.6.
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115 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) such effects in the original model specification, but without going to the extreme of adding a variable (k-factor)
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116 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER sit submode(s) are used along the transit path.
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117 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) subject to some degree of simulation variation.
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118 Part 1: ACTIVITY-BASED TRAVEL DEMAND MODELS: A PRIMER used to obtain valid logsum parameters, such as including distance impedance variables in the destination-choice models in addition to the mode choice logsum variables.) What potential activity-based model users should take away from this discussion is that the best way to model destination choice in relation to or in combination with mode choice remains an issue that could benefit from further research and testing in practice.
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119 Chapter 3: ACTIVITY-BASED MODEL CONCEPTS AND ALGORITHMS (FOR MODELERS) this case, however, it is not as critical because the trip-level models do not have as much influence on the model results as the tour-level models -- they simply provide some more detail based on the tour-level choices.
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