The Exploratory Advanced Research Program Fact Sheet
Experiments on Driving under Uncertain Congestion
Conditions and the Effects on Traffic Networks from
Congestion Pricing Initiatives
When and why drivers choose a priced or
tolled facility versus an untolled but congested
parallel route is the subject of a 3-year project
funded
by
the
Federal
Highway
Administration’s
(FHWA)
Exploratory
Advanced Research (EAR) Program, in
partnership with the University of Central
Florida and Georgia State University.
“Experiments on Driving under Uncertain
Congestion Conditions and the Effects on
Traffic
Networks
from
Congestion
Conditions and the Effects on Traffic
Networks
from
Congestion
Pricing
Initiatives” is examining how driver’s risk
preferences influence their choice of route
and travel departure time.
Background
Understanding
drivers’
reactions
to
congestion pricing initiatives has been limited
partly due to the type of data commonly
collected. Stated preference data are simply
responses to surveys asking for intended
responses to congestion pricing, lacking clear
incentives for respondents to answer
truthfully and accurately. While useful for
some purposes, these methods are known to
generate biased and volatile responses. This
study is using experimental economics to
make observations on actual choices with
precise monetary incentives. The participant
pool is drawn from drivers
in Orlando, Florida and
Atlanta,
Georgia.
Participants receive travel
options
with
actual
consequences,
primarily
involving money, where the
choice situations vary with
respect to congestion and
congestion pricing. The
overall objective is to
understand why drivers
change their route choices when tolls change.
A particular focus is the extent to which
response differences depend on varying
preferences and perceptions of travel times
and travel time reliability. The study is
exploratory because many of the instruments
and procedures have not previously been
employed for the purposes of generating
behavioral data on policy issues, in the way
that they are in this study.
This study assesses the responses to several
congestion pricing schemes. Three basic types
of experiments were conducted: a field
experiment using GPS instruments; a multidriver traffic simulation experiment; and a
single driver simulator experiment, all using
field participants. The field experiment and
the single-driver simulator experiments are
individual choice experiments with no
interactions between participants. The multidriver traffic simulator is a group experiment
where the traffic conditions are endogenously
generated by the simultaneous, but
independent, choices of the participants.
Experimental Economics Tools
Experimental economics, and the closely
related field of cognitive psychology, utilizes
laboratory experiments in addition to field
observations to understand complex, naturally
occurring, market systems and choices. The
market mechanism of priced lanes assumes
that drivers will differentiate
themselves as to route choice
but there is little understanding
as to the mechanisms for that
differentiation. Studies of the
SR-91 in California show that
income level is not a strong
determinate and although 42%
of commuters use the lanes,
few commuters are everyday
users. The UCF/GSU study is
examining the role of risk
preferences and travel time perceptions in
route choice. A route choice represents a type
of lottery with an expected pay-off (travel
time) and costs (toll vs. non-toll).
Field Experiments
We studied drivers in four regions: an eastside
and a west side commuter route in Orlando,
and a north-east and a north-west commuter
route in Atlanta. All participants’ cars were
outfitted with a Global Positioning System
(GPS) device that receives but does not send
signals, allowing the researchers to collect
information on driving habits. All driving data
is downloaded directly from the device to a
computer at meetings with the researchers.
Approximately two weeks passed between
each meeting: this time frame was determined
by the capacity of the GPS device’s ability to
store data of participants’ travel log. Each
driver faced a choice between taking two
routes during morning or evening commute.
One route was an express way and the other a
local route, roughly parallel to each other.
Each drive was only about five miles long,
and up to 20 drives were paid during the two
weeks between study meetings. During the
first two week drive period each driver was
simply paid a fixed fee each time there was a
valid recorded drive, up to the maximum of
20 drives. The subsequent two drive periods
involved additional surcharges and subsidies
that varied by route. These incentives varied
across drivers, and across driver periods, but
each driver faced the same net incentive
during each drive period.
Lab Experiments
TO LEARN MORE
For more information
on this EAR Program
project, contact Karen
White at 202-3669474, email:
Karen.white@dot.gov
The simulator driving tasks involved driving a
car in a computer simulation and choosing
between various routes to get from the origin
to the destination. Earnings depend on the
length of time and on the choice between a
tolled and a non-tolled route. The simulator
tasks are conducted on the same participants
that drive in our commuter study using GPS.
These tasks are required to assess the risk
attitudes of drivers and any characteristic
biases in how they form beliefs over travel
times from experiences. In all these tasks the
consequences are real money, not just
hypothetical. In addition, participants
responded to a socio-demographic
questionnaire, an opinion questionnaire about
congestion policies, and a traffic survey about
their driving habits and congestion
experiences. Together, the field and lab data
will be used to model how driver
characteristics interact to determine the use of
tolled routes.
Status
Over 480 drivers in Atlanta and Orlando have
participated in the study. In addition 200
students have also participated in testing
whether student behavior can predict field
drivers’ behaviors. Driving behavior is
characterized in terms of risk attitudes, and
risk perceptions. Preliminary analysis of the
data shows comparability of risk attitudes
across tasks as well as regions, and that
students behave in many ways similarly to
field drivers. These preliminary findings
demonstrate the possibility that these
simulator methods will provide useful data at
relatively small additional costs for a variety of
transportation issues.
In December, 2011 the research received
positive peer review from academics in the
areas of experimental economics and road
pricing at a FHWA organized workshop. The
research will move on to understand demand
elasticity related to tolls and congestion as well
as the potential for revenue-maximizing or
welfare-maximizing tolls.