Dr. Stephen Boyles, Assistant Professor in the Department of Civil, Architectural and Environmental Engineering at The University of Texas at Austin, presented “Transportation Networks and Optimization” on July 25, 2012, at the Cockrell School of Engineering as part of a series of presentations by and for students engaged in transportation research.
This summer at the Cockrell School of Engineering, student exploring transportation research as a potential career are learning the many directions that such a career can take them. UT Austin professors, Center for Transportation (CTR) researchers, and students are presenting topics of interest as part of the Undergraduate Summer Internship in Transportation (USIT). USIT is sponsored by the Advanced Institute for Transportation Infrastructure Engineering and Management, an organization whose mission is to increase the number, quality, and diversity of professionals entering the transportation sector.
Different regions have drastically different transportations challenges and needs, said Dr. Stephen Boyles to the USIT student interns at UT Austin. He contrasted the needs of Austin, Seattle, and Laramie, to make his point.
“Geography matters,” said Dr. Boyles, “in planning a transportation network. Seattle has lots of hills — and trains aren’t efficient at climbing hills.” Mountains, lakes, rivers, and a major port create unique transportation challenges in Seattle, Washington.
Boyles said, “In Austin, Texas, the infrastructure was not built to handle the growth” that the city has experienced over the last several decades, making congestion the major area of concern for transportation planners where the greater metropolitan area contains more than one million residents.
Managing traffic is something that Dr. Boyles has experienced on a very direct, hands-on level: he worked as a flow operator, directing the flow of traffic from a command station, opening and closing ramp meters to keep traffic moving efficiently.
In Laramie, the third largest city in Wyoming with a population of about 25,000, congestion is not the main concern.
“Safety during cold weather and managing transportation needs on a small budget” are the major concerns, said Boyles. “Truck drivers traveling through Laramie are not prepared when a snow storm develops in late May.” Weather conditions can be extreme in Laramie, which is located on a high plain between two mountain ranges, where winter storms develop later in the year due to its northerly location.
Currently, Dr. Boyles research focus is on large-scale transportation systems for multi-city regions. Study in network modeling for large systems includes such issues as vehicle routing, traffic assignment/equilibrium, network design, congestion pricing, logistics and supply chain models, and land use forecasting.
He discussed traffic management and Austin’s challenges, particularly in relation to traffic flowing through a U.S. supercorridor: IH 35, which runs from Mexico to Canada.
“Most trucks on IH 35 are going through Texas, not to Austin,” Boyles said. That knowledge was part of what led to the development of SH-130, a parallel, tolled roadway, which was intended to take some of the truck traffic off IH 35. It was expected that more trucks would use the SH-130, but at this time truck usage has been less than expected, while automobile usage is higher than expected.
One of the primary goals of SH-130 was to relieve congestion in downtown Austin. But how many drivers will choose to use it and how much revenue can be generated by tolling this roadway? The history of this network and how it is being used by travelers is a good example of what can be learned through the study of road networks.
When developing road networks, planners consider factors such as travel time impacts, demand, and potential revenue. How can we predict the routes that drivers will take? The question can also be phrased: Why do drivers choose particular routes?
Travelers consider such factors as consistency of travel time, safety, and fuel economy. Everyone would like to take the fastest route. But due to the phenomena of user equilibrium, all routes end up with approximately the same travel time. If one route is faster, more drivers choose it. This leads to higher congestion on that path, making travel time longer on that route until it reaches a state of equilibrium with the alternate route. The principle of user equilibrium states that the travel time on every route being used must be equal and minimal. If this were not so, everyone would switch to a different route to reduce their travel time.
Complicating the issue of network modeling is a factor known as the Braess paradox. Paradoxical to common sense, adding capacity can sometimes increase travel time for all routes.
The Braess paradox states (from Wikipedia): “For each point of a road network, let there be given the number of cars starting from it, and the destination of the cars. Under these conditions one wishes to estimate the distribution of traffic flow. Whether one street is preferable to another depends not only on the quality of the road, but also on the density of the flow. If every driver takes the path that looks most favorable to him, the resultant running times need not be minimal. Furthermore, it is indicated by an example that an extension of the road network may cause a redistribution of the traffic that results in longer individual running times.”
Dr. Boyles referenced another belief that does not translate well in the field of network modeling: the “invisible hand” theory of economics, a term economists use to describe the self-regulating nature of the marketplace. The term was first used by Scottish economist and philosopher Adam Smith. Dr. Boyles defined the “invisible hand” roughly as “the economy goes where it wants to go without apparent direction or oversight.” This theory is often seen as effective because the owner of a service is best rewarded by providing the service that the majority of people want, thereby maximizing profits and rewards.
But in contrast, Dr. Boyles described the classic “prisoner’s dilemma,” where individual choices lead to unexpected outcomes. Briefly put, in the prisoners’ dilemma: you and a friend are arrested committing a crime. If you both stay silent, you both go to jail for 1 year. If you testify against your friend but they stay silent, you get off free, but they go to jail for 15 years. If you both testify against each other, you both go to jail for 14 years.
In the prisoner’s dilemma, when both parties act selfishly, it leads to the worst possible outcome. The suggestion is that network modeling must take a part in managing congestion, rather than allowing the “invisible hand” of individual driver choices to determine how traffic will best flow.
In the end, in determining which route a traveler will choose, the answer is often: “It depends.” Yet, it is important to try to predict route choices, although it is not easy to do. This is why there is a great need for research to be done in the area of network modeling, as the world’s networks increase in complexity.
Dr. Boyles’ areas of research study include network modeling, dynamic traffic assignment, transportation user behavior, and infrastructure systems. Dr. Boyles can be reached at email@example.com
For more information on Dr. Boyles, visit his bio page at the Cockrell School of Engineering. http://www.ce.utexas.edu/faculty-directory/profiles/stephen-boyles.html
Faculty and professional researchers presenting topics of interest this summer include Dr. Zhanmin Zhang, Dr. C. Michael Walton, Rob Harrison, Dr. Kara Kockelman, Dr. Randy B. Machemehl, Dr. Chandra Bhat, Dr. Stephen Boyles, Lisa Loftus-Otway, and Dr. Amit Bhasin.
Students participating in the USIT internship are exposed to active transportation research programs that cover a wide range of topics, including systems analysis, materials, design, management, traffic engineering and planning, modeling, testing, and multimodal systems. USIT is sponsored by the Advanced Institute for Transportation Infrastructure Engineering and Management, an organization whose mission is to increase the number, quality, and diversity of professionals entering the transportation sector.
Many of the transportation research projects discussed at USIT events are conducted through the Center for Transportation Research. UT Austin faculty and student researchers perform the research and produced research reports and products. Much of the work is funded by the Texas Department of Transportation.
Links to More Information
Civil, Architectural & Environmental Engineering (CAEE) at UT Austin