From January 17 through 18, 2020, the University of California, Irvine (UCI) and sponsor Pacific Southwest Region University Transportation Center (PSR) hosted the Third Annual Irvine Symposium on Emerging Research in Transportation (ISERT 2020). Each year, this Symposium brings together academics, researchers, graduate students, and industry professionals in transportation to exchange ideas on emerging research and applications in transportation. ISERT spotlights new research ideas that may still be under development or that involve preliminary results. This is the third in a series of articles detailing the Symposium itself as well as individual presenters.

UCI doctoral student, Irene Martinez, participated in ISERT as a speaker, presenting her research on the Location Problem for Variable Speed Limit (VSL) Application Areas. Originally from Barcelona, Spain, Martinez completed her undergraduate degree in Civil Engineering at Polytechnic University of Catalonia (BarcelonaTech), then a masters under the supervision of Professor Wen-Long Jin at UCI. After completing her master’s degree, she began entered the PhD program at UCI and has been researching on several traffic flow and transportation related topics since.

At ISERT 2020, Martinez presented her research on the location of variable speed limits (VSL) control to reduce capacity drop effects on bottlenecks, based on traffic simulations. VSLs are a popular freeway control strategy that limits the vehicle’s speed in real time, adapting to changing traffic or weather conditions. Many studies consider VSL as a mainline traffic control strategy, where the traffic demand to a given location is controlled by lowering the speed limit upstream of that point. Since this type of strategy can control the number of vehicles that reach the bottleneck, VSL control has been considered a viable option to prevent traffic breakdown at bottlenecks. Studies mainly focus on the design of the speed itself; the location of the VSL application area, another important design variable, is often neglected.

^{Irene Martinez poses humbly alongside her work.}

Martinez presented an analysis of the stationary states that can be found when a VSL control is applied upstream of a bottleneck. “When a congested (not desired) state takes place, it limits the flow to the dropped capacity (around 10% lower than the actual bottleneck capacity) due to the capacity drop phenomenon,” explained Martinez. However, she added that if the VSL is designed carefully, both considering the speed limit and the location of the application area, another uncongested state can be observed, with a higher flow (the bottleneck capacity). During the presentation, Martinez demonstrated how the location of a VSL control area is a crucial design variable to ensure that vehicles accelerate freely (at their maximum acceleration rate) from the VSL zone. When vehicles are in this maximum acceleration state, and they go through the bottleneck without stopping, the capacity drop phenomenon can be prevented. “Moreover, it is shown that the required distance between the VSL control and the bottleneck increases with increasing speed limits, which contradicts the intuitive arguments that were used in the literature until now to establish the location of the VSL application area,” Martinez said. She also noted that this work is the first to analytically identify, formulate, and solve the optimal location problem for variable speed limit application areas.

Commenting on her research, Martinez notes that in order to reduce traffic congestion, we need a full understanding of both the demand (departure time choice, mode choice, etc.), the supply (the physical capacity that the roads have to accommodate the demand), and their interactions. "We live in a new era where technology enables us to measure, track and control (traffic) in real time. We should take advantage of this! Transportation scientists and traffic engineers can design how the vehicles should move in order to maximize the efficiency of the transportation system," says Martinez.

Martinez has received several awards and fellowships which include Abertis First National (Spanish) and International Prizes for Transportation Research and the Balsells Mobility Fellowship, has two journal publications, has lived in four different countries, and speaks five languages.

Besides being a prospective researcher, Martinez loves to play piano and dance. Recently, she developed a new passion for gardening.

We wish Irene Martinez best of luck in future endeavors and look forward to what will certainly be many more accomplishments.

About the Author:

Adylbek Abdykalikov is a recent graduate student of the Masters of International Public Policy and Management Program at USC Price. He has working experience in various positions at the Ministries of Transport and Communication and Investment and Development of Kazakhstan and was in charge of Transportation and Civil Aviation policy development and implementation. He served as the lead writer to METRANS Newsletter and lead student event coordinator for METRANS and PSR.