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Model Task Force Meeting November 29, 2007
Activity-based Modeling
from an Academic Perspective
Transportation Research Center (TRC)
Dept. of Civil & Coastal Engg.
University of Florida
Siva Srinivasan
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
Model Task Force Meeting November 29, 2007
Home
Work
Lunch
Shop
Drop-off Kid at School
7:15 am
7:30 am
8:00 am
7:35 am
12:30 pm 12:35
pm
1:00 pm
1:05 pm5:00 pm
5:30 pm6:00 pm
6:30 pm
Car-pool
Drive-alone
Drive-alone
Drive-alone
walk
walk
Consider the travel pattern of a person………
Critique of the Trip-based Approach
Drive
Drive
Drive
Drive
Walk
Walk
H A1
H
P3
P4
P5
P6
A2
A3
A4
A5
A6
One Home-based Other trip
Four Non home-based trips
Peak
Peak
Peak
Peak
Off Peak
Off Peak
Critique of the Trip-based Approach
The trip-based method views this person’s travel as:
Model Task Force Meeting November 29, 2007
One Home-based Shop trip
Trip Generation
(frequency)
Trip Distribution
(destination)
Mode Split
(mode)
Network Assignment
(route)
Link flows, speeds, travel times, transit-ridership, etc.
• Socio-economic characteristics
• Land-use patterns
• Transportation system characteristics
Model Task Force Meeting November 29, 2007
The analytical modeling procedure is the “four-step” process
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
Model Task Force Meeting November 29, 2007
Work
Shopping
Drive alone
Drive alone Drive alone
Very Good Transit Service
Transit
Drive AloneDrive Alone
Critique of the Trip-based Approach
Home
HomeWork Shop
Example 2: Effect of Transit Improvements (alternate responses)
Drive alone
Drive alone
Drive alone
HomeShop
Drive alone
Drive alone
Home
HomeWork
Transit Transit
Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach
5:00 pm
5:15 pm
5:40 pm
6:00 pm
4:00 pm
4:15 pm
4:40 pm
5:00 pm
4:00 pm
4:30 pm
5:40 pm
6:00 pm
Example 3: Employer-based Demand-Management Actions
Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach
Home
Home
Work Pick-up child
ShopDrop-off child
Person 1
Person 2
Example 4: Inter-personal Dependencies and Indirect Effects
Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach
Home Hom
e
Work
Person 1
Pick-up child
ShopDrop-off childPerson 2
Model Task Force Meeting November 29, 2007
Critique of the Trip-based Approach
Example 4: Inter-personal Dependencies and Indirect Effects
What is the Activity-based Approach?
Model Task Force Meeting November 29, 2007
Home
Work
Lunch
Shop
Drop-off Kid at School
7:15 am
7:30 am
8:00 am
7:35 am
12:30 pm 12:35
pm
1:00 pm
1:05 pm5:00 pm
5:30 pm6:00 pm
6:30 pm
Car-pool
Drive-alone
Drive-alone
Drive-alone
walk
walk
The activity-based method views the travel pattern as………
Model Task Force Meeting November 29, 2007
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 Work
LunchShop
Space constraints:
Location of home, school, and work are fixed
Time constraints:
School and work timings
Total time = 24 hours & that includes time for sleeping, eating etc.
Inter-personal constraints:
Household task allocations
Joint travel of household members
What is the Activity-based Approach?
Model Task Force Meeting November 29, 2007
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
Home
Work
Lunch
Shop
Drop-off Kid at School
7:15 am
7:30 am
8:00 am
7:35 am
12:30 pm
12:35 pm
1:00 pm1:05 pm5:00 pm
5:30 pm6:00 pm
6:30 pm
Car-pool
Drive-alone
Drive-alone
Drive-alone
walk
walk
Home
School
7:15 am
7:30 am
Car-pool
4:00 pm
4:15 pm
Car-pool
What is the Activity-based Approach?
Contrasting Trip-based and Activity-based Methods:
Summary of Conceptual Differences
Model Task Force Meeting November 29, 2007
Treatment of travel as though demanded on their own right
Individual trip is the unit of analysis
Internal consistency of the travel pattern NOT guaranteed
Impacts of personal and household constraints not captured
Represents time as simply a cost of making a trip and time-of-day of travel is not captured adequately
Treatment of travel as a derived demand
Activity-travel pattern is the unit of analysis
Ensures internal consistency of the activity-travel pattern
Accommodates the impacts of various constraints on activity-travel decision making
Models travel within the context of overall daily time-use (both durations and time-of-day)
Trip-based Activity-based
Contrasting Trip-based and Activity-based Methods:
Summary of Modeling Differences
Model Task Force Meeting November 29, 2007
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 off-peak factors
Duration and timing of activities and travel
Feasibility of Adopting Activity-based Methods
Model Task Force Meeting November 29, 2007
(1) Activity-based models are “complicated”
Yes…
There are several (definitely more than four) components in the model-system
Could employ advanced econometric methods
However…
The conceptual modeling approach is more intuitive and easier to explain
The overall complexity depends on what dimensions of the activity pattern we are modeling
Statistical software to estimate the advanced econometric models available
Model Task Force Meeting November 29, 2007
(2) Activity-based models are data intensive
Yes…
Household travel surveys are needed for model estimation
Disaggregate forecasts of future population characteristics needed for model application
However….
Activity-based models can be developed using data collected from currently-used household-travel-survey methods
In fact, activity-based methods make better use of the data we are currently collecting
Methods (Iterative Proportional Fitting) for synthesizing disaggregate population characteristics are available
Feasibility of Adopting Activity-based Methods
Model Task Force Meeting November 29, 2007
(3) Activity-based models are computationally demanding
Yes….
More model components / disaggregate approach / probabilistic models requiring micro-simulation to determine choice outcomes
Requires significant run times and very large data processing capabilities
However…
Computers are only becoming faster !
Parallel processing, multi-threading, efficient database management methods are available
Can use clever sampling techniques
Feasibility of Adopting Activity-based Methods
Model Task Force Meeting November 29, 2007
(4) There are no standardized procedures or software
Yes…
Unlike the trip-based approach, there is no one single well-established procedure for modeling activity-patterns
There are no rigorous comparative assessments of the different modeling methods
There are no generic software platforms for implementing activity-based methods
However…
There are common underlying structures across the different activity-based models that can provide guidelines on developing one for any region
There is considerable flexibility in customizing the modeling approach for the activity-travel dimensions of interest for any region
Feasibility of Adopting Activity-based Methods
Model Task Force Meeting November 29, 2007
(5) Other Issues
Activity-based models have predominantly focused on internal, person travel – external travel and freight movements are not yet within this framework
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
Still need to make the models “empirically” useful
Incorporation of appropriate traveler characteristics
Choice of resolution for space and time
Inclusion of appropriate land-use descriptors
Inclusion of appropriate transportation system descriptors
Feasibility of Adopting Activity-based Methods
Concluding Thoughts
Model Task Force Meeting November 29, 2007
• 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 ??