Education

Research Description

Dr. Hajbabaie is interested in real-time optimization of large-scale complex engineering systems represented by models with a high degree of realism. His research is focused on traffic operations and control in the presence of connected human-driven and self-driving cars. Dr. Hajbabaie and his research group use multi-scale analysis, modeling, and optimization to improve traffic operations. His research is advancing our understanding of cooperative traffic control systems and contributes to the development of future mobility systems, including connected and automated vehicles.

Honors and Awards

• Certificate of Excellence, Work Zone and Traffic Control Committee, the Transportation Research Board, National Academy of Sciences, 2019
• Outstanding Junior Researcher, the Department of Civil and Environmental Engineering, Washington State University, 2018
• Best Paper Award, Transportation Research Record: Journal of the Transportation Research Board, Work Zone Traffic Control Committee, 2016
• Best Student Paper Award, Transportation & Development Institute’s Congress, American Society of Civil Engineers, 2011
• Best Paper Award, Institute of Transportation Engineers, Illinois Section, 2010

Publications

Stochastic Gradient-Based Optimal Signal Control With Energy Consumption Bounds

Islam, S. M. A. B. A., Aziz, H. M. A., & Hajbabaie, A. (2020), IEEE Transactions on Intelligent Transportation Systems, 1–14. https://doi.org/10.1109/TITS.2020.2979384

A consensus-based distributed trajectory control in a signal-free intersection

Mirheli, A., Tajalli, M., Hajibabai, L., & Hajbabaie, A. (2019), Transportation Research Part C: Emerging Technologies, 100, 161–176. https://doi.org/10.1016/j.trc.2019.01.004

A decomposition scheme for parallelization of system optimal dynamic traffic assignment on urban networks with multiple origins and destinations

Mehrabipour, M., Hajibabai, L., & Hajbabaie, A. (2019), Computer-Aided Civil and Infrastructure Engineering, 34(10), 915–931. https://doi.org/10.1111/mice.12455

Cooperative traffic signal and perimeter control in semi-connected urban-street networks

Mohebifard, R., Islam, S. M. A. B. A., & Hajbabaie, A. (2019), Transportation Research Part C: Emerging Technologies, 104, 408–427. https://doi.org/10.1016/j.trc.2019.05.023

Distributed Optimization and Coordination Algorithms for Dynamic Traffic Metering in Urban Street Networks

Mohebifard, R., & Hajbabaie, A. (2019), IEEE Transactions on Intelligent Transportation Systems, 20(5), 1930–1941. https://doi.org/10.1109/TITS.2018.2848246

Optimal network-level traffic signal control: A benders decomposition-based solution algorithm

Mohebifard, R., & Hajbabaie, A. (2019), Transportation Research Part B: Methodological, 121, 252–274. https://doi.org/10.1016/j.trb.2019.01.012

Development of a signal-head-free intersection control logic in a fully connected and autonomous vehicle environment

Mirheli, A., Hajibabai, L., & Hajbabaie, A. (2018), Transportation Research Part C: Emerging Technologies, 92, 412–425. https://doi.org/10.1016/j.trc.2018.04.026

Distributed optimization and coordination algorithms for dynamic speed optimization of connected and autonomous vehicles in urban street networks

Tajalli, M., & Hajbabaie, A. (2018), Transportation Research Part C: Emerging Technologies, 95, 497–515. https://doi.org/10.1016/j.trc.2018.07.012

Dynamic speed harmonization in connected urban street networks

Tajalli, M., & Hajbabaie, A. (2018), Computer-Aided Civil and Infrastructure Engineering, 33(6), 510–523. https://doi.org/10.1111/mice.12360

Dynamic traffic metering in urban street networks: Formulation and solution algorithm

Mohebifard, R., & Hajbabaie, A. (2018), Transportation Research Part C: Emerging Technologies, 93, 161–178. https://doi.org/10.1016/j.trc.2018.04.027

View all publications via NC State Libraries

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Grants

NCHRP- Guide for the Formulation of Long-Range Plans and Budgets for Replacement of Highway Operations Equipment

Federal Highway Administration (FHWA)(5/18/20 - 2/17/22)

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NCHRP- Guide for the Formulation of Long-Range Plans and Budgets for Replacement of Highway Operations Equipment

Sponsor: Federal Highway Administration (FHWA)

Start Date: 5/18/20

End Date: 2/17/22

Abstract

State highway agencies own and maintain a substantial number of operations equipment assets, which are diverse in type and condition. The operations equipment are critical components for delivery of State highway agency programs, projects, and services and contribute to a significant portion of capital investments. Operations equipment assets generally deteriorate as they age resulting in rising operations and maintenance costs and decreasing salvage values. The deterioration conditions and technological changes motivate agencies to replace a portion of their equipment fleet periodically. Operations equipment assets require recurring maintenance, operational expenditures, as well as timely replacement to retain their value and achieve their anticipated level of performance, reliability, and economy. According to practical considerations also highlighted in the NCHRP Project 13-04 (Hamilton, 2018), budget cuts often hit the replacement funds, as a fast solution to expenditure reduction. However, in the long run, keeping, operating, and maintaining an aged fleet may cost highway fleet agencies and public more than a younger fleet. For instance, maintenance and repair costs of an aged equipment increase, as does its downtime, both of which directly affect the service delivery and task accomplishment capacities. Besides, the service level of old equipment is often limited: its increased downtime hours lead to under-performance and/or inefficient performance of essential services. Therefore, rather than short-term solutions that may not efficiently save resources, fleet management forces shall be equipped with adequate tools and effective strategies for making long-range (i.e., 20-25 years) plans and budgets for replacement of highway operations equipment. The existing replacement decision frameworks are usually based on a desire to minimize the total or expected life-cycle fleet costs, including those related to the acquisition, operations and maintenance, and salvage value. Yet, life-cycle costs may not capture the fleet management needs and budgets over a long-range horizon. Therefore, current practices, although representing scientific rigor and practical aspects of fleet management strategies, may lack the background required for long-range fleet management. In fact, there is no widely accepted process for determining the long-range plans and budgets for replacement of highway operations equipment. Therefore, there is a need to develop a practically feasible and theoretically sound methodology for long-range equipment replacement planning that accommodates the needs of highway agencies and their budget constraints. Literature presents various solutions to making investment decisions for highway operation equipment (e.g., Hamilton 2018; Fan et al. 2015). A variety of practices and strategies have been used by State departments of transportation (DOTs) and highway agencies to make investment decisions for highway operation equipment, while taking the diverse classifications of such assets into careful consideration. For instance, as of 2002, Florida has used thresholds for mileage or age to determine vehicle replacement priorities. For example, full-size pickups are replaced at 8 years or 95,000 miles and dump trucks at 10 years or either 150,000 or 250,000 miles depending on capacity (Weissmann & Weissmann 2002). Besides, Kim et al. (2009) conducted a study to improve the Oregon DOT’s existing fleet replacement model. The study confirmed that most DOTs used fixed thresholds as a primary factor in equipment replacement decisions. These fixed thresholds for replacement decisions do not yield the optimal fleet management criteria, especially over a long horizon. Texas Department of Transportation (TxDOT) has used the Texas Equipment Replacement Model (TERM) to identify equipment pieces as candidates for replacement one year in advance. TxDOT’s equipment operations system (EOS) captures extensive information on all aspects of equipment operations. EOS considers three criteria for replacement: 1) equipment age, 2)

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Preparing for Traffic Signal operations in a Multi-Modal Connected & Autonomous Vehicle Environment

Washington State Department of Transportation(8/16/19 - 8/31/20)

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Preparing for Traffic Signal operations in a Multi-Modal Connected & Autonomous Vehicle Environment

Sponsor: Washington State Department of Transportation

Start Date: 8/16/19

End Date: 8/31/20

Abstract

Washington State Department of Transportation (WSDOT) maintains 1,000 signalized intersections throughout the state. Development of a real-time, reliable, and multimodal signal timing approach to use CV information offers great potential to reduce congestion and its associated costs significantly, and also places WSDOT in a unique position to take on the FHWA SPaT challenge. WSDOT needs a strategic approach for how to prepare for the SPaT challenge and other opportunities that lead to the installtion of CV requipment that will connect real-time signal operations to surrounding CVs. The proposed research project will enable WSDOT to determine why, when, and where a connected arterial should be implemented from technological and traffic operational perspectives. Furthermore, WSDOT can predict the expected outcomes more accurately. Connected vehicles are coming and WSDOT needs to be ready for them. The proposed project will offer significant enhancements to the operations of signal systems in response to passenger cars, pedestrians, bicyclists, and transit systems. It will also enable WSDOT to identify technological issues and requirement of integrating CV hardware in existing traffic signal systems. Washington State University’s initial tests indicate a reduction in passenger cars’ travel time between 18% and 34% in a fully connected vehicle environment. The proposed project will reduce travel time in urban street networks by controlling the timing of signalized intersections and could be expanded in the future to control ramp meters on on-ramps to improve traffic operations on freeway facilities as well. Furthermore, it will help WSDOT with identifying the right time and location for selecting a corridor for the SPaT challenge so that the technological needs and compatibilities are met and expected outcomes are significant. he primary objective of this project is to help WSDOT with identifying the right time and location for selecting a corridor for the SPaT challenge so that the technological needs and compatibilities are met and expected outcomes are significant. The secondary objective of the proposed research is to develop a real-time methodology to control the timing of signalized intersections in a multi-modal and connected transportation network. The proposed approach not only can be used to control the signals in semi-connected and fully connected corridors, it also determines the location, ideal implementation date (with respect to CV penetration rates), and expected benefits of connected corridors from both operational and technological stand points.

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NCDOT University Transportation Center of Excellence on Mobility and Congestion

NC Department of Transportation(2/01/20 - 7/31/22)

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NCDOT University Transportation Center of Excellence on Mobility and Congestion

Sponsor: NC Department of Transportation

Start Date: 2/01/20

End Date: 7/31/22

Abstract

The NCDOT is launching a bold and forward-looking effort to establish multi-university transportation centers of excellence to provide broad-based, multidisciplinary research into the applications and impacts of cutting edge technologies and emergent, disruptive trends. The projects included in our center proposal were custom-built to address the research areas spelled out in the request for proposals for the desired Mobility and Congestion center. The three themes are as follows: • Theme #1: Big Data and Data-Driven Transportation Management and Decision Support • Theme #2: Active Transportation Management/Integrated Corridor Management • Theme #3: Transit and Mobility as a Service

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Evaluation of Life Cycle Impacts of Intersection Control Type Selection

NC Department of Transportation(8/16/13 - 2/29/16)

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Evaluation of Life Cycle Impacts of Intersection Control Type Selection

Sponsor: NC Department of Transportation

Start Date: 8/16/13

End Date: 2/29/16

Abstract

The primary research objective is to provide guidance on intersection improvements when upgrading a TWSC intersection. Current practice tends to focus more on the short term cost and benefits, whereas the objective of this project will be met by looking at short and long term cost and benefits across all spectrums. The final product should aid in making decisions that could ultimately save tax payers millions of dollars ? diverting funds to be used for other roadway improvements in a time when funds are scarce.

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IMAP-Assessment of Benefits/Costs, Route Selection, and Prioritization

NC Department of Transportation(8/16/13 - 5/15/16)

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IMAP-Assessment of Benefits/Costs, Route Selection, and Prioritization

Sponsor: NC Department of Transportation

Start Date: 8/16/13

End Date: 5/15/16

Abstract

In 2003 and 2004, a joint research team from the University of North Carolina School of City and Regional Planning and North Carolina State University Department of Civil, Environmental, and Construction Engineering conducted a benefit cost study of the North Carolina Department of Transportation?s Incident Management Assistance Patrol (IMAP) program investments. In the roughly ten years since this study, NCDOT's IMAP program coverage has grown from approximately 320 centerline miles in 2004 to approximately 690 centerline miles today. IMAP drivers provide the critically important service of minimizing congestion impacts of incidents while simultaneously maximizing the safety of the motorists and emergency responders. The system growth highlighted above is a testament to the success of IMAP drivers and supervisors of in providing this service. A direct result of this overwhelming success is that demand for further expansion of the IMAP program continues unabated. However, this need to move forward with expanding IMAP service areas corresponds to a trend in NCDOT workforce downsizing. Fiscal and personnel constraints are not unique to North Carolina and have directly impacting how service patrols have been deployed elsewhere. In fact, SafeHighways.org estimates that about 39% of safety service patrols nationwide are run by private contractors. Much has changed since the earlier NCDOT-sponsored IMAP research project. The tool delivered by that project did not consider outsourcing as an option for IMAP expansion. There has also been much research over the last ten years that can be applied to yield much improved estimates both of system costs and also of transportation network benefits from well-designed IMAP deployments. Buoyed by this motivation, the NC State/ITRE project team proposed to conduct a thorough review of the state of the practice and well as applicable research to provide new methodologies implemented in an accompanying computational engine that will enable NCDOT to conduct accurate assessments of IMAP program costs and benefits, including evaluation of public and private delivery of service options, and to conduct selection and prioritization of routes for IMAP system expansion.

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