Analyzing Travel Demand Management Strategies: the Promise of Activity-Based Travel Demand Models

Analyzing Travel Demand
Management Strategies: the Promise of Activity-
Based Travel Demand Models

Elizabeth A. Sall

SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY
Transportation Research Board Annual Meeting
Sunday January 13th, 2013

Overview of Questions I Hope to Answer

1. What is an “Activity-Based Travel Demand Model”?
2. What is it about these activity models make them
better (or not) for analyzing TDM Strategies?
3. What does a specific TDM strategy look like in an
activity model? (a few examples)
4. Who has these activity models anyways?

SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY 2

Activity-Based Travel Demand Model?
A few principles

• People want to do activities, and they travel in order
to participate in them  travel is a derived demand.


A few principles

• Household and social structures influence activity
and travel  there‟s a lot more to „you‟ than the zone
around you.

Flickr: MNicoleM


A few principles

• No cart before the horse / driving home if you
walked to work / leaving work before you got there
 interdependence explicitly recognized.

If it looks like But you don’t
this outside have a car at
every morning… work now…

then you’ll So even if
probably the evening auto
decide to… commute is cake,
you’ll need to…


A few principles

• No cart before the horse driving home if you walked
to work / leaving work before you got there 
interdependence explicitly recognized.

If this area where you You realize that if
work has a congestion you drive like this
fee from 4 to 6 pm… In the AM…

That it will cost
you like this $
In the PM…
And you live here…


A few principles

Sum of all small behavior types is the majority of
behavior  we are all unique, and that is important.

0.18
0.16
0.14 Income $0-30k
P robability Dens ity

Income $30-60k
0.12 Income $60-100k
0.1 Income $100k+

0.08
0.06
0.04
0.02
0
$- $5 $10 $15 $20 $25 $30
Value of T ime ($/Hour)



What it comes down to:
• A less-cool-looking version of sim-city.



Every Sim has a:
• role
• income
• age
• gender
• household

Population Synthesis



Every Worker Sim
chooses a workplace
based on:
• Job type/income
match
• Accessibility to work

Workplace Destination Choice



Every Sim Household
decides how many cars
they want:
• How easy is it to get to
work with and without
a car?
other stuff around the
house with and
without a car?
• Demographics
Auto Availability



Every morning, each Sim
wakes up and asks
themselves “Gee, what
am I going to do today?”
work?
• What else do I need to
do today?
• Demographics

Tour Generation



If they are going
somewhere other than to
work, the Sim will pick
what the primary reason
for leaving the house is:
• Accessibility
• Schedule

Tour Destination Choice



Then they need to pick
the primary way that they
are going to get there.
• Accessibility by mode

Tour Mode Choice



If they need to make
stops along the way, they
pick places that are
convenient to the tour
mode that they have
chosen to their primary
destination.
• How far a detour is it
from my main trip?
• Near transit transfer
point/freeway exit?
Intermediate Stop Choice



Once the entire tour is
planned out, the Sim
choses the exact mode
that they will use for each
sub-part of their
excursion from home
(aka tour).

Trip Mode Choice



Based on congestion
levels and other
preferences, the Sim then
navigates their way
through the network to
participate in activities
and carry out their plans.

Route Choice



All of these choices are
carried out by the
individual with full
knowledge of their:
• Other choices
• Activity needs /
Household
• Physical / Temporal
constraints
• Demographics


Good for TDM Strategy Analysis?

• Depends on the strategy. Can it be represented in
ABM framework? Can it be just as well represented
in 4S model?
• Existing Tools? Do you already have an AB model?
• Got Data? Does the data already give you the answer
to the question that you have?
• Risk/Reward? Depends on the questions that you
need to have answered and how sure you want to be
about them.
(And if you can‟t articulate a question that you are trying to answer, there are much more
rewarding places to sink time and money)


ABM -- Good for TDM Strategy Analysis?
Pros

• Understands induced and latent demand
 If you build that HOT lane, more people are going to
drive.
 If you make it easier to park, more people are going
to drive.
 Hard to build your way out of congestion.


Pros

• Explicit representation of interdependencies
 If my child has swim practice, I need to drive today.
 If I need to stay late at work and transit is bad after
rush hour, I will drive.
 If I bike down a hill, I have to bike back up it.

Bike Accessibility To Bike Accessibility From

Pros

• Lots of choices for performance measures
 Each sim is tracked and can be accounted for
individually or across multiple demographic or
geographic dimensions.
Future GHG Production per HH

sfmobility.org


Pros

• Simulation framework is flexible
 You can “do something else” to your Sim
 Your Sim can become aware of new information
 Your Sim‟s decisionmaking can have
more/new/better rules or models


Pros

• Simulation framework is flexible
 Our Sims just learned about the benefits of bike lanes

Trip Difference - Bike Projects
Daily Tours v4.1 Harold v4.3 Fury
Bike 500 0.1% 3,000 0.8%
Walk 1,100 0.0% -500 -0.0%
Transit 850 0.0% -600 -0.0%
Auto -2,400 -0.0% -1,300 -0.0%
Total 0 0.0% 600 0.0%


Pros

• Can easily implement what if scenarios:
 Can still do sans data. Test a hypothesis!
What if we had a compressed work week?

We could assume that:
 commuting would be 20% less
 work duration a few hours longer
 only full time workers affected

Tested in Burlington:
 -4% overall trips
 Only slight VMT decrease


- Pros

• Understand the system
• Recognize unintended consequences
 Can we build our way out of GHG issues with bike
lanes?
 If our transit system becomes the most popular thing
on earth how many people would ride it?


Cons

• Is it overkill ?
• Is it easier to run a pilot and find out vs. spend a few
years and $1 million developing a model ?
• Do you really just need a back of the envelope guess?

….but once you have it you will find so many questions
that it is good at answering.


Who has these tools?


Thanks for inviting me
to this community to speak!

(we are open to suggestions about how to
provide info for better decisions)
elizabeth@sfcta.org
www.sfcta.org/modeling

SAN FRANCISCO COUNTY TRANSPORTATION AUTHORITY

“…A major advantage of activity based modeling lies in
its ability to give a better understanding and prediction
of traveler responses to TDM measures and other
types of transportation policies. “
“ These improved estimates of the changes in important
transportation variables, then, provide the basis for the
development of more accurate estimates of emission
reductions that would result from the implementation
of one or more TDM strategies.”
Shiftan Y. et al “Activity-based Modeling as a Tool for Better
Understanding Travel Behaviour” IATBR Conference
Paper. Lucern, 10-15 August 2003.


“…trip based four step aggregate methodology, is
inadequate in analyzing the sustainable transport
policies. “
“A review of … activity based travel demand modeling
found that they are capable of handling such policies
better than conventional models and are assistive to
the decision makers in arriving at right mix of polices
specific to the situations. ”

Malayath, Manoj and Ashish Verma. “Activity based travel
demand models as a tool for evaluating sustainable
transportation policies” Research in Transportation
Economics Volume 38/Issue 1. Feb 2013.


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