Activitybased Modeling from an Academic Perspective Siva Srinivasan
Activity-based Modeling from an Academic Perspective Siva Srinivasan Transportation Research Center (TRC) Dept. of Civil & Coastal Engg. University of Florida Model Task Force Meeting November 29, 2007
Overview 1. A critique of the trip-based method 2. What is the activity-based approach? 3. Feasibility of adopting activity-based methods 4. Concluding thoughts Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach Consider the travel pattern of a person……… 7: 30 am Car-pool 7: 35 am Drop-off Kid at School 7: 15 am Drivealone 8: 00 am walk 12: 30 pm 12: 35 pm Work Home 5: 00 pm 6: 30 pm Lunch 1: 05 pm 1: 00 pm Drivealone 6: 00 pm Drivealone walk 5: 30 pm Shop Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach The trip-based method views this person’s travel as: One Home-based Other trip H Drive Peak A 1 Four Non home-based trips P 3 One Home-based Shop trip Drive Peak P 5 Drive Peak Walk Off Peak A 4 A 5 A 2 P 6 Model Task Force Meeting A 3 Peak P 4 H Drive Walk Off Peak A 6 November 29, 2007
Critique of the Trip-based Approach The analytical modeling procedure is the “four-step” process Trip Generation (frequency) • Socio-economic characteristics • Land-use patterns • Transportation system characteristics Trip Distribution (destination) Link flows, speeds, travel times, transitridership, etc. Mode Split (mode) Network Assignment (route) Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach The fundamental role of travel-demand models is to enable us perform quantitative assessments of the impacts of policy actions The policy actions being considered these days may invoke complex behavioral responses from travelers which cannot be adequately captured within a trip-based framework Some Illustrative Examples…. . Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach Example 1: Effect of Transit Improvements Drive alone Transit Very Good Transit Service Work Drive Alone Drive alone Shopping Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach Example 2: Effect of Transit Improvements (alternate responses) Drive alone Home Work Transit Home Model Task Force Meeting Home Shop Drive alone Transit Work Drive alone Home Drive alone Shop Home November 29, 2007
Critique of the Trip-based Approach Example 3: Employer-based Demand-Management Actions 5: 15 pm 5: 40 pm 6: 00 pm 5: 00 pm 4: 15 pm 4: 40 pm 6: 00 pm 4: 30 pm Model Task Force Meeting 5: 00 pm 5: 40 pm November 29, 2007
Critique of the Trip-based Approach Example 4: Inter-personal Dependencies and Indirect Effects Person 1 Pick-up child Work Home Drop-off child Person 2 Model Task Force Meeting Shop November 29, 2007
Critique of the Trip-based Approach Example 4: Inter-personal Dependencies and Indirect Effects Person 1 Work Home Drop-off child Shop Person 2 Pick-up child Model Task Force Meeting November 29, 2007
What is the Activity-based Approach? The activity-based method views the travel pattern as……… 7: 30 am Car-pool 7: 35 am Drop-off Kid at School 7: 15 am Drivealone 8: 00 am walk 12: 30 pm 12: 35 pm Work Home 5: 00 pm 6: 30 pm Lunch 1: 05 pm 1: 00 pm Drivealone 6: 00 pm Drivealone walk 5: 30 pm Shop Model Task Force Meeting November 29, 2007
What is the Activity-based Approach? The conceptual modeling procedure is……… (1) Activity Generation: Choose what out-of-home activities have to be undertaken during the day incorporating relevant constraints Drop-off Kid at School Lunch Work Shop Space constraints: Time constraints: Inter-personal constraints: Location of home, school, and work are fixed School and work timings Household task allocations Total time = 24 hours & that includes time for sleeping, eating etc. Joint travel of household members Model Task Force Meeting November 29, 2007
What is the Activity-based Approach? The conceptual modeling procedure is……… (2) Activity Scheduling: Sequence the activities into a “chain” or “pattern”. Travel is a consequence of this sequencing – the need to move from one location to another at certain times of the day to participate in the different activities 4: 00 pm Car-pool School 7: 35 am 7: 30 am am Car-pool 7: 15 am am Drop-off Kid at School 8: 00 am walk 12: 35 pm 12: 30 pm Work 4: 15 pm Home 6: 30 pm Drivealone 6: 00 pm Model Task Force Meeting Drivealone 5: 00 pm Drivealone 5: 30 pm Shop Lunch 1: 00 pm 1: 05 pm walk November 29, 2007
Contrasting Trip-based and Activity-based Methods: Summary of Conceptual Differences Trip-based Activity-based ü Treatment of travel as though demanded on their own right ü Treatment of travel as a derived demand ü Individual trip is the unit of analysis ü Activity-travel pattern is the unit of analysis ü Internal consistency of the travel pattern NOT guaranteed ü Ensures internal consistency of the activity-travel pattern ü Impacts of personal and household constraints not captured ü Accommodates the impacts of various constraints on activity-travel decision making ü Represents time as simply a cost ü Models travel within the context of of making a trip and time-of-day of overall daily time-use (both durations travel is not captured adequately and time-of-day) Model Task Force Meeting November 29, 2007
Contrasting Trip-based and Activity-based Methods: Summary of Modeling Differences Trip-based Activity-based Number of HB and NHB trips Generation and sequencing of activities Zonal-level trip attractions & gravity model for trip-end locations Location of activity participation Mode for each trip Mode for linked trips (tours) Time of day using peak and offpeak factors Duration and timing of activities and travel Model Task Force Meeting November 29, 2007
Feasibility of Adopting Activity-based Methods (1) Activity-based models are “complicated” Yes… Ø There are several (definitely more than four) components in the model-system Ø Could employ advanced econometric methods However… Ø The conceptual modeling approach is more intuitive and easier to explain Ø The overall complexity depends on what dimensions of the activity pattern we are modeling Ø Statistical software to estimate the advanced econometric models available Model Task Force Meeting November 29, 2007
Feasibility of Adopting Activity-based Methods (2) Activity-based models are data intensive Yes… Ø Household travel surveys are needed for model estimation Ø Disaggregate forecasts of future population characteristics needed for model application However…. Ø Activity-based models can be developed using data collected from currently-used household-travel-survey methods Ø In fact, activity-based methods make better use of the data we are currently collecting Ø Methods (Iterative Proportional Fitting) for synthesizing disaggregate population characteristics are available Model Task Force Meeting November 29, 2007
Feasibility of Adopting Activity-based Methods (3) Activity-based models are computationally demanding Yes…. Ø More model components / disaggregate approach / probabilistic models requiring micro-simulation to determine choice outcomes Ø Requires significant run times and very large data processing capabilities However… Ø Computers are only becoming faster ! Ø Parallel processing, multi-threading, efficient database management methods are available Ø Can use clever sampling techniques Model Task Force Meeting November 29, 2007
Feasibility of Adopting Activity-based Methods (4) There are no standardized procedures or software Yes… Ø Unlike the trip-based approach, there is no one single well-established procedure for modeling activity-patterns Ø There are no rigorous comparative assessments of the different modeling methods Ø There are no generic software platforms for implementing activity-based methods However… Ø There are common underlying structures across the different activity-based models that can provide guidelines on developing one for any region Ø There is considerable flexibility in customizing the modeling approach for the activity-travel dimensions of interest for any region Model Task Force Meeting November 29, 2007
Feasibility of Adopting Activity-based Methods (5) Other Issues Ø Activity-based models have predominantly focused on internal, person travel – external travel and freight movements are not yet within this framework Ø The activity-patterns have to be aggregated to OD trip tables by time-of-day if dynamic traffic assignment techniques are to be used -- these may not necessarily be straight forward Ø Still need to make the models “empirically” useful ü Incorporation of appropriate traveler characteristics ü Choice of resolution for space and time ü Inclusion of appropriate land-use descriptors ü Inclusion of appropriate transportation system descriptors Model Task Force Meeting November 29, 2007
Concluding Thoughts • Activity-based methods are theoretically and intuitively better descriptors of the travel-generation process • The fundamental advantage of activity-based approach is in terms of more providing more realistic behavioral responses to land-use and transportation system changes • The practical necessity of activity-based methods (and the structure of this model) for any region depends on what kinds of questions we want the travel-demand model to answer for this region • It does appear that the “questions” are rather different for different regions as are data and resource availability • Customization of the modeling methodology to different regions is more appropriate ? ? Model Task Force Meeting November 29, 2007
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