Drivers’ willingness-to-pay to reduce travel time: evidence from the San Diego I-15 congestion pricing project

TLDR: Using revealed preference data from a congestion pricing demonstration project in San Diego, the authors estimate that willingness to pay to reduce congested travel time is higher than previous stated preference results, although this may be biased upward by drivers' perception that the toll facility provides safer driving conditions.

Abstract: The adoption of congestion pricing depends fundamentally upon drivers’ willingness to pay to reduce travel time during the congested morning peak period. Using revealed preference data from a congestion pricing demonstration project in San Diego, we estimate that willingness to pay to reduce congested travel time is higher than previous stated preference results. Our estimate of median willingness to pay to reduce commute time is roughly $30 per hour, although this may be biased upward by drivers’ perception that the toll facility provides safer driving conditions. Drivers also use the posted toll as an indicator of abnormal congestion and increase their usage of the toll facility when tolls are higher than normal.

Figures

Table 1. Demographic Characteristics by Mode Choice (In percentages except last column)

Figure 1. FasTrak Tolls for October and November, 1998

Figure 5. Time Savings Associated with Use of Ted Williams Bypass On-ramp (October – November, 1998)

Figure 4. Day-to-Day Variation in Average Time Savings for Express Lanes for Lane Arrivals from 7:31 to 8:00 AM (October – November, 1998)

Figure 3. Time Savings Associated with Express Lanes Use

Table 3. Logit Choice Model

Full text

UC Berkeley
Earlier Faculty Research
Title
Drivers' Willingness-to-Pay to Reduce Travel Time: Evidence from the San Diego I-15
Congestion Pricing Project
Permalink
https://escholarship.org/uc/item/3mx1d1k4
Authors
Brownstone, David
Ghosh, Arindam
Golob, Thomas F
et al.
Publication Date
2002-05-01
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University of California

Drivers’ Willingness-to-Pay to Reduce Travel Time: Evidence
from the San Diego I-15 Congestion Pricing Project
David Brownstone
Department of Economics
University of California
Irvine, CA 92697-5100
Tel: +1-949-824-6231
Fax: +1-949-824-2182
Email: dbrownst@uci.edu
Arindam Ghosh
Department of Economics
University of California
Thomas F. Golob
Institute of Transportation Studies
University of California
Camilla Kazimi
Department of Economics
San Diego State University
Dirk Van Amelsfort
Bureau Goudappel Coffeng
The Netherlands
Revised Draft
May 2002
To be published in:
Transportation Research, Part A: Policy and Practice.

2
Drivers’ Willingness-to-Pay to Reduce Travel Time: Evidence from the
San Diego I-15 Congestion Pricing Project
Abstract
The adoption of congestion pricing depends fundamentally upon drivers’ willingness to
pay to reduce travel time during the congested morning peak period. Using revealed
preference data from a congestion pricing demonstration project in San Diego, we
estimate that willingness to pay to reduce congested travel time is higher than previous
stated preference results. Our estimate of median willingness to pay to reduce
commute time is roughly $ 30 per hour, although this may be biased upward by drivers’
perception that the toll facility provides safer driving conditions. Drivers also use the
posted toll as an indicator of abnormal congestion and increase their usage of the toll
facility when tolls are higher than normal.

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Drivers’ Willingness-to-Pay to Reduce Travel Time and Its Variance:
Evidence from the San Diego I-15 Congestion Pricing Project
INTRODUCTION
Policy makers have been hesitant to adopt congestion pricing despite the fact that
economists have been championing the cause for many decades. A fundamental
question in the debate is how much drivers are willing to pay to save time by avoiding
congested roadways. Most revealed preference (RP) “value of time” estimates are
based upon mode choice models for the tradeoff between transit and auto travel. Small,
1992, and Wardman, 1998 provide comprehensive reviews of value-of-time studies,
MVA Consultancy et. al., 1994, reviews the theoretical background and empirical
studies done in U.K. summarizing value of time estimates for different modes of travel,
Small et. al., 1999 review value of time studies from reducing time on congested roads,
and Gonzalez, 1997, provides a review of the theory of consumer choice and its
connection to value of time and mode choice modeling. It has been pointed out in the
literature that value of time estimates from comparing auto travel to transit may be
biased by the extent to which real differences between crowded public buses, light-rail,
or private automobiles are not captured by the model.
Calfee and Winston (1998) attempt to estimate willingness to pay to reduce travel time
that is specific to automobile travel, thus excluding inter-modal biases. They use stated
preference data because they lacked revealed preference data for the choices involved
with congestion pricing. Based on this approach, Calfee and Winston (1998) conclude
that commuters have a lower valuation of time saving than previously thought.
We estimate willingness to pay to reduce median travel time specific to travel by
automobile on a congested road. The approach uses revealed preference data from
the I-15 congestion pricing project in San Diego. Our results indicate that willingness to
pay to save time is much higher than Calfee and Winston's estimates. Our estimates

4
are similar to Lam and Small (2001) who also use revealed preference data from
another California toll facility.
We find that the median willingness to pay to reduce travel time for the population of
regular morning drivers is roughly $30 per hour. This estimate explicitly controls for the
variability in time savings over the month around the survey date. Variability is
measured by the difference between the 90
th
percentile and the median time savings
from using the toll facility. This measure captures the notion that drivers are concerned
mostly about unexpected delays in their morning commutes. We also control for
unusual congestion by including the deviation of the actual from the mean toll for the
time the commuter travels the corridor, and we find that drivers are willing to pay much
more to avoid unusual congestion (as evidenced by a higher than usual toll). At the
time drivers need to decide whether or not to use the toll facility, they only know the
distribution of time savings, tolls, and the actual toll (but not the actual time savings for
the particular trip). Our choice model specification is designed to mimic the information
available to the commuter.
Since the toll lanes along the I-15 are separated from the rest of the freeway, users may
also benefit from improved driving conditions and safety. Willingness to pay estimates
would therefore include drivers’ valuation of these benefits, and may therefore be
upward biased estimates of pure willingness to pay for travel time reduction. However,
because all current and proposed congestion toll facilities also require separation from
the main traffic lanes, we would expect these benefits to carry over to similar toll
facilities.
Our models all assume that drivers do not change their departure times from home in
response to changes in tolls and congestion levels. While this assumption is probably
false, imposing this assumption should not bias our willingness to pay estimates since
the congestion pricing scheme insures that the toll per minute of time saved is roughly
constant over the morning commute period. It would be better to jointly model

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Drivers’ willingness-to-pay to reduce travel time: evidence from the san diego i-15 congestion pricing project" ?

Their estimate of median willingness to pay to reduce commute time is roughly $ 30 per hour, although this may be biased upward by drivers ’ perception that the toll facility provides safer driving conditions. 

Q2. How long does the Express Lanes run?

The Lanes are operated in the southbound direction from approximately 5:30AM to 10:00AM and in the northbound direction from 2:30PM to 7:30PM. 

Q3. How many people carpooled on the last morning?

of those who carpooled on their last morning, 22.5% reported solo driving on the main lanes of I-15 at least once during the previous week, and 10.6% reported solo driving using FasTrak during this same period. 

Q4. What is the reason for the reversals of the expected variability effects for part of our?

One possible explanation for the reversals of the expected variability effects for part of their sample is that the toll also provides information about upcoming congestion, and the effects of variability are conditional on mean and actual tolls in their specification. 

Q5. What is the effect of the toll facility on drivers?

Since the toll lanes along the I-15 are separated from the rest of the freeway, users may also benefit from improved driving conditions and safety. 

Q6. What is the likely effect of carpooling on the time saving?

When considering carpool choice as compared to solo driving, the results indicate that carpooling is more likely to be chosen than solo driving as the number of workers per vehicle increases, for longer distance trips, for non-commute trips, and when a carpool bypass onramp is available. 

Q7. What is the effect of assuming fixed departure times?

Incorrectly assuming fixed departure times should not bias their willingness to pay estimates since the congestion pricing scheme insures that the toll per minute of time saved is roughly constant over the morning commute period. 

Q8. How many minutes of time can a person save by using the Express Lanes?

Users of the dedicated Express Lanes onramp at Ted Williams Parkway can gain up to five minutes additional time if they choose FasTrak (toll) or carpool modes. 

Q9. Who led the team that collected the panel survey data?

Kathy Happersett of the Social Science Research Laboratory of San Diego State University led the team that collected the panel survey data. 

Q10. What is the effect of the proposed toll facilities on drivers?

because all current and proposed congestion toll facilities also require separation from the main traffic lanes, the authors would expect these benefits to carry over to similar toll facilities. 

Q11. What are the likely demographic variables to choose FasTrak over solo driving?

individuals between 35 and 44 years old, individuals with education beyond a bachelor’s degree, and homeowners are also more likely to choose FasTrak over solo driving. 

Q12. What are the generic variables that vary across the alternative?

The generic variables that vary across alternatives are: (1) toll price, (2) median time savings, (3) difference between actual and mean toll, and (4) reduction in variability of time savings from Express Lanes use. 

Q13. What is the toll variable for the carpool and solofree alternatives?

The toll variable is zero for the carpool and solofree (solo driving in the main lanes) alternatives, and the authors also set it to zero for the small number of respondents who report that they did not pay for their toll charges. 

Q14. How many times were the speeds measured?

These speeds were measured every fifteen minutes of the morning peak period for five days and were found to be generally 70 miles per hour with little variation across day and time. 

Q15. How were the speeds measured along the Express Lanes?

Speeds along the Express Lanes were measured by driving the lanes, recording start and end times, and then calculating average speed using the time differential and distance traveled.