Education

Research Description

Dr. Hajbabaie's 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 advances our understanding of cooperative traffic control systems and contributes to the development of future mobility systems, including connected and automated vehicles.

Honors and Awards

• Best Dissertation Award – Honorary Mention, Transportation Research Board, 2022
• Sweet 16 High Value Research, American Association of State Highway and Transportation Officials, 2021
• 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

Connected autonomous vehicles: State of practice

Islam, M. M., Newaz, A. A. R., Song, L., Lartey, B., Lin, S.-C., Fan, W., … Karimoddini, A. (2023, May 25), APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Vol. 5. https://doi.org/10.1002/asmb.2772

Effects of Connectivity and Automation on Saturation Headway and Capacity at Signalized Intersections

Hajbabaie, A., Tajalli, M., & Bardaka, E. (2023), Transportation Research Record: Journal of the Transportation Research Board, 8. https://doi.org/10.1177/03611981231187386

White Phase Intersection Control Through Distributed Coordination: A Mobile Controller Paradigm in a Mixed Traffic Stream

Niroumand, R., Hajibabai, L., & Hajbabaie, A. (2023), IEEE Transactions on Intelligent Transportation Systems, 24(3), 2993–3007. https://doi.org/10.1109/TITS.2022.3226557

A Distributed Gradient Approach for System Optimal Dynamic Traffic Assignment

Mehrabipour, M., & Hajbabaie, A. (2022), IEEE Transactions on Intelligent Transportation Systems, 23(10), 17410–17424. https://doi.org/10.1109/TITS.2022.3163369

An Enhanced Cell Transmission Model for Multi-Class Signal Control

Islam, S. M. A. B. A., & Hajbabaie, A. (2022), IEEE Transactions on Intelligent Transportation Systems, 23(8), 11215–11226. https://doi.org/10.1109/TITS.2021.3101838

Battery Electric Vehicles Network Equilibrium With Flow-Dependent Energy Consumption

Niroumand, R., Bahrami, S., Aashtiani, H. Z., & Hajbabaie, A. (2022), Transportation Research Record: Journal of the Transportation Research Board, 2677(5), 444–462. https://doi.org/10.1177/03611981221131813

Distributed cooperative trajectory and lane changing optimization of connected automated vehicles: Freeway segments with lane drop

Tajalli, M., Niroumand, R., & Hajbabaie, A. (2022), Transportation Research Part C: Emerging Technologies, 143, 103761. https://doi.org/10.1016/j.trc.2022.103761

Effects of Autonomous Driving Behavior on Intersection Performance and Safety in the Presence of White Phase for Mixed-Autonomy Traffic Stream

Niroumand, R., Hajibabai, L., Hajbabaie, A., & Tajalli, M. (2022), Transportation Research Record: Journal of the Transportation Research Board, 2676(8), 112–130. https://doi.org/10.1177/03611981221082580

Testing Connected Vehicle-Based Accident Mitigation for Red-Light Violation Using Simulation Strategies

Tajalli, M., Al Islam, S. M. A. B., List, G. F., & Hajbabaie, A. (2022), Transportation Research Record: Journal of the Transportation Research Board, 2676(6), 583–600. https://doi.org/10.1177/03611981221075630

Traffic Signal Timing and Trajectory Optimization in a Mixed Autonomy Traffic Stream

Tajalli, M., & Hajbabaie, A. (2022), IEEE Transactions on Intelligent Transportation Systems, 23(7), 6525–6538. https://doi.org/10.1109/TITS.2021.3058193

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Grants

Establishing Best Practices and Technical Guidance for Planning and Developing an EV Infrastructure Network

NC Department of Transportation(7/01/23 - 6/30/25)

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Establishing Best Practices and Technical Guidance for Planning and Developing an EV Infrastructure Network

Sponsor: NC Department of Transportation

Start Date: 7/01/23

End Date: 6/30/25

Abstract

Electric vehicle (EV) technology encourages sustainability benefits by reducing environmental pollution primarily associated with transportation-related activities. With the EV market share anticipated to exceed half of all new vehicles sold by 2040, there is an urgency to begin preparing for an EV future now. Therefore, there is a need to develop a statewide EV network expansion plan that requires establishing policies, planning practices, technical siting guidance, and electric power grid requirements designed to accommodate an extensive EV charging load. On the other hand, to ensure EV charging access is accessible throughout the state, including historically underserved communities such as rural areas and communities of concern, equity best practices must be established and incorporated into the plans. A failure to create a viable and reliable EV infrastructure and associated policies will hinder EV adoption and exacerbate the health and environmental impacts caused by the transportation sector. The proposed Project will develop a series of planning and policy best practices and technical guidance for siting EV charging infrastructure to support the expansion of the charging network and its management in North Carolina. This research will assess local planning policies and power utility considerations to develop guidance that informs the efficient and equitable development of a statewide EV charging network plan. The policy and planning research tasks will result in a practice-ready guidance document. This document will include guidance for local agencies, draft policies that can be locally adopted to simplify EV infrastructure permitting and approvals at the municipal and county level, and guidance that highlights opportunities for NCDOT to collaborate and support external partners in improving statewide EV infrastructure. Additionally, the technical guidance derived from models for siting EV charging infrastructure will support the charging network’s expansion and provide insights on charger deployments given geographical limitations, travel demand constraints, electric power grid requirements, and equity considerations, among other concerns. The research results will be practice-ready, implementable guidance on EV network siting and development. The policy and planning best practice and EV development guidance can be used to support MPO, RPO and local planning agencies for siting local EV infrastructure and developing planning policy that encourages the establishment of an equitable and technically sound EV charging infrastructure.

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Evaluating Benefits and Drawbacks of Intersections with Three-Phase Traffic Signals

NC Department of Transportation(8/01/22 - 7/31/24)

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Evaluating Benefits and Drawbacks of Intersections with Three-Phase Traffic Signals

Sponsor: NC Department of Transportation

Start Date: 8/01/22

End Date: 7/31/24

Abstract

The purpose of this research is to add new insights regarding the benefits and drawbacks of using intersections with three-phase traffic signals compared to other intersection designs and to develop a technical guideline to help designers and policymakers in transportation understand when and where to use three-phase designs. At four-phase conventional intersections where traffic demand is near or above capacity, innovative intersections may perform better. New designs with two-phase traffic signals such as reduced conflict intersections (RCI, also called RCUT and superstreet) result in shorter travel times, fewer crashes, and better pedestrian service in North Carolina (NC). However, retrofits to designs with two-phase signals may be impactful and unpopular. Higher minor street demand, lack of precedent, and complaints (from neighbors, business owners, politicians, media, etc.) are among the possible obstacles for constructing two-phase designs in many locations. In other words, while two-phase intersections perform very well at many intersections, designers might not be able to select those designs for some projects. On the other hand, intersections with three-phase signals might provide some of the two-phase design advantages while also providing more direct movements and alleviating some public concerns. This study seeks to answer the following questions: (1) At what locations are three-phase designs most well suited? (2) How much do they cost, especially compared with other intersections like RCIs? (3) What kind of traffic control devices (pavement markings, traffic signs, and traffic signals) are needed? (4) What movement restrictions could cause motorist confusion and violations? (5) How could we minimize those violations? (6) What are the considerations needed for pedestrian and bicyclist safety? (7) What kind of geometric and right-of-way (ROW) limitations are faced during construction? (8) What movements are less impactful for redirecting in different cases? (9) What designs would be most readily accepted by the public? Current literature on innovative intersections with three-phase signals is limited. Excluding offset, partial continuous-flow intersections (CFIs), and quadrant intersections, (three common three-phase designs in NC) little information is available on the performance of other three-phase intersections. Reviewing the Crash Modification Factors (CMF) Clearinghouse reveals that only a few studies have estimated CMFs for converting four-phase conventional intersections to three-phase intersections. These studies focused on partial CFIs and partial median U-turn intersections (MUTs). Other possible three-phase designs should also be evaluated to increase the confidence level in selecting the most appropriate design. A recent presentation by NCDOT’s Dr. Joseph Hummer introduced ten three-phase intersections as possible candidates for future projects. Based on initial evaluations, the ten three-phase designs could show potential in improving existing intersections. The research team also proposes another new three-phase design which could be considered as a promising design. The proposed three-phase intersection redirects two left-turn and one through movements. It is expected to experience higher capacity for the proposed design compared to conventional intersection due to better signal progression and a lower volume to capacity (v/c) ratio. Also, the proposed design has 19 conflict points. Only two of the existing three-phase designs (reverse RCI and offset intersections) have fewer conflict points compared to the proposed design. This proposed study focuses on the following three-phase designs: partial MUTs, partial CFIs, reverse RCIs, thru- cuts, offset, quadrant, CFI/MUT combo, redirect one minor leg, redirect minor lefts, seven-phase signal, and redirect two lefts and a through intersection (see Figure 1 in the body of the proposal). Also, the research team will consider other new designs, especially where another proposed design might perf

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Guidance on Considering CAVs in Travel Demand Models

NC Department of Transportation(8/01/22 - 7/31/24)

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Guidance on Considering CAVs in Travel Demand Models

Sponsor: NC Department of Transportation

Start Date: 8/01/22

End Date: 7/31/24

Abstract

By the year 2045 or 2050 Connected and Automated Vehicles (CAVs) have the potential to significantly disrupt travel demand across North Carolina. The North Carolina Department of Transportation is currently planning the infrastructure that will serve our travels needs in 2045 and beyond. There is an urgent need for NCDOT to better understand the potential effects of CAVs on travel demand and traffic forecasts, as a failure to do so could lead to big implications for NCDOT and the citizens of North Carolina. This research will provide guidance to NCDOT on possible modification of parameters and assumptions within the Regional Travel Demand Model (RTDM) Development Guidelines, including possible modifications to the standardized procedures related to CAVs. This guidance will be informed by scenario testing that will consider different levels of CAV penetration, various impacts on travel demand parameters (including changes in land use), and various impacts on supply parameters. This research will also provide guidance on the consideration of CAVs in the more advanced model structures found in the Triangle, Triad and Greater Charlotte regions, and areas not covered by the RTDM Development Guidelines.

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SCC: Serving Households in AReas with food Insecurity with a Network for Good: SHARING

National Science Foundation (NSF)(10/01/21 - 9/30/25)

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SCC: Serving Households in AReas with food Insecurity with a Network for Good: SHARING

Sponsor: National Science Foundation (NSF)

Start Date: 10/01/21

End Date: 9/30/25

Abstract

How can we create “community food security”? This project aims to develop a community-based socially intelligent nonprofit food rescue and distribution infrastructure to fairly serve vulnerable communities experiencing food insecurity. This infrastructure will have a loop mechanism that continuously learns consumer preferences and provides feedback to upstream stages of the supply chain and also learns about the food availability at the local food sources and feeds that information to the downstream stages. The main objective of this research is to minimize food waste along different stages of the supply chain while maximizing equitable access to safe food given consumer preferences. Food banks are nonprofit organizations that provide a framework for the non-profit food supply chain by collecting donations from multiple sources such as local grocers, growers, and the community (e.g., food drives) and distributing the donations to food-insecure households through a network of community-based partner agencies (e.g., food pantries, homeless shelters, schools). The COVID-19 pandemic has significantly strained this network as demand has surged, the volunteer-based workforce has waned, and supply uncertainty has increased highlighting both the network’s strengths and limitations and the need to strengthen the community-based infrastructure and create solutions that are self-reliant and robust for communities that are affected by such events.

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RAPID: Supporting Efficient and Equitable COVID-19 Vaccine Distribution and Administration: Exploring Challenges and Opportunities through Data Analytics

National Science Foundation (NSF)(6/01/21 - 5/31/23)

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RAPID: Supporting Efficient and Equitable COVID-19 Vaccine Distribution and Administration: Exploring Challenges and Opportunities through Data Analytics

Sponsor: National Science Foundation (NSF)

Start Date: 6/01/21

End Date: 5/31/23

Abstract

The objective of this RAPID project is to identify and document possible issues of the existing COVID-19 vaccine distribution and administration systems and propose solutions through collecting national vaccine distribution and administration data and quantifying lead times and various performance measures. We plan to collect day-to-day vaccine allocation and shipment data (to track the supply over time) and vaccine administration data from CDC and States. More information on data elements is available in the research plan section. While this data is available at CDC now, it is not available to the public and it is not archived for a long time (as is the case for N1H1 vaccination data) and will be lost if not collected now. We will work with reporters that have collaborated with us before to create a freedom of information act (FOIA) request to access and archive the data. State record this data as well; however, they do not follow a consistent way of reporting the data, and the majority of them only report cumulative data. It is not certain whether they record the daily data, and if so, how long they keep it. As such, the daily data is at great risk of being lost if not collected as soon as possible and many important vaccination data and trends will be lost if the day-to-day data is not available.

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Groundwork for the Second Edition of the Alternative Intersection and Interchange Informational Report (2022-011)

NC Department of Transportation(8/01/21 - 8/31/23)

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Groundwork for the Second Edition of the Alternative Intersection and Interchange Informational Report (2022-011)

Sponsor: NC Department of Transportation

Start Date: 8/01/21

End Date: 8/31/23

Abstract

Alternative Intersection and Interchange (AII) designs are those which provide an innovative approach to the geometric or control features which may improve operations and/or safety for different road users. In 2010, the U.S. Federal Highway Administration (FHWA) published the first edition of “Alternative Intersection and Interchange Informational Report” (AIIR), which provided information on six alternative treatments including displaced left-turn (DLT) intersections, restricted crossing U-turn (RCUT) intersections, median U-turn (MUT) intersections, quadrant roadway (QR) intersections, double crossover diamond (DCD) interchanges, and DLT interchanges. For each treatment, AIIR presented detailed information in a standardized format, including salient geometric design features, operational and safety issues, access management, costs, construction sequencing, environmental benefits, and applicability. The AIIR first edition has been employed by various agencies as a valuable resource for planning and designing AIIs, there are still unconventional design concepts that have not been fully explored and some of the current ones could use updates. During the past decade, there have been an increasing number of AIIs installed in the United States, and more new AII designs that are not documented in AIIR first edition have emerged since 2010, such as Reverse RCUTs, Partial Median U-turns, and Grade-Separated Alternative Intersections, etc. These new AII designs may involve different traffic organization patterns, which may introduce confusion and create safety hazards for drivers. NCDOT is a national leader in AII implementation, which provides safe, efficient, and cost-effective travel solutions for North Carolina drivers. Therefore, the primary objective of this research is to start the process of compiling the AIIR Second Edition. Specifically, this research will provide a state-of-the-practice literature review and expert interviews on AII designs, draft an annotated outline for the AIIR second edition, and develop an updated set of simulation models to assess the performance of various AII designs. Finally, this research will provide practical recommendations for planners and engineers to select site-specific AII designs during project processes.

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STRIDE: Integrated Corridor Management: Cooperative Signal Control with Freeway Operations and Ramp Metering

US Dept. of Transportation (DOT)(8/16/20 - 8/31/23)

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STRIDE: Integrated Corridor Management: Cooperative Signal Control with Freeway Operations and Ramp Metering

Sponsor: US Dept. of Transportation (DOT)

Start Date: 8/16/20

End Date: 8/31/23

Abstract

STRIDE: Integrated Corridor Management

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

Federal Highway Administration (FHWA)(5/18/20 - 5/31/22)

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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: 5/31/22

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 - 12/31/20)

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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: 12/31/20

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 - 2/28/23)

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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: 2/28/23

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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