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Sponsor: RIMI

Joint Estimation of a Semi-Markov Decision Process Model of Vacant Taxi Matching and Routing

Joint Estimation of a Semi-Markov Decision Process Model of Vacant Taxi Matching and Routing

Abstract

We formulate a vacant ride-sourcing or taxi driver’s routing decision as an infinite-horizon semi-Markov decision process (SMDP) in a road network, where a driver decides which link to take at each node and transitions to a new node depending on the stochastic vehicle-passenger matching process. A driver’s decision is based on observable and unobservable states.

The modeler’s job is to jointly estimate an average driver’s parameterized utility function as well as the state transition function based on the sequence of observed states and actions. We establish the existence and uniqueness of a fixed point solution to the Bellman equation for the SMDP, which is needed for the maximum likelihood estimation of model parameters. We use parallel computing to speed up the estimation algorithm to be applicable to a case study in a large network.

The expected fare, expected operating cost and number of intersections in the urban area are found to be significant predictors of drivers’ routing decisions. Comparison with several base models suggest the advantage of considering multiple decision cycles, low discount rate (corresponding to a discount factor close to 1), and joint estimation of routing and matching parameters.

Song Gao is Professor of Civil and Environmental Engineering at the University of Massachusetts Amherst. Her research focuses on travel behavior and transportation system analysis, with applications in smart and shared mobility, transportation planning, and sustainable transportation systems, and has been funded by local, regional and federal government agencies and private foundations, including the Massachusetts Department of Transportation, National Science Foundation, FHWA, and APRA-E. Prior to joining UMass, Prof. Gao worked as a transportation engineer at Caliper Corporation. She is an Editorial Board Editor of Transportation Research Part B, and past Associate Editor of Transportation Science. She received her Ph.D. and M.S. in Transportation from MIT, and B.S. in Civil Engineering from Tsinghua University.

Changing Transit Ridership and Service During the COVID-19 Pandemic

Status

Complete

Project Timeline

March 1, 2022 - June 30, 2023

Principal Investigator

Michael HylandMichael Hyland

Sponsor, Program & Award Number

RIMI: RIMI-4H

Areas of Expertise

Public Transit, Shared Mobility, & Active Transportation

Team Departmental Affiliation

Civil and Environmental Engineering

Project Summary

The COVID-19 pandemic spurred a period of significant change in travel behavior in the United States. Increased working from home, teleconferencing, telelearning, and e-commerce changed how travelers perceive, interact with, and use public transportation and shared mobility. According to the Federal Transit Administration, at the start of the pandemic public transit ridership in the U.S. dropped by 79% between 2019 and 2020. While some riders have returned, public transit ridership remains below pre-pandemic levels. Transit operators may be serving different needs, as post-pandemic travel behavior and the use of other forms of shared mobility (such as microtransit and transportation network companies) continues to evolve. Public transit operators have also been impacted by new pandemic-related procedures, service cuts, and staffing shortages. This project will explore how the pandemic impacted public transportation and shared mobility to inform policy recommendations that can help the state maximize the effectiveness of shared and active transportation options. It will examine the current state of public transit, how transit agencies can evolve into this new context, and how other shared modes have been impacted by the pandemic. The project will also assess how micromobility (both personally owned and shared) can fill gaps in public transit networks caused by California’s changed post-pandemic travel demand. It will also examine the role that active transportation infrastructure can play in improving safety and environmental outcomes, enhancing social equity, and economic development in a variety of built environments.

Policy Brief Series on the Role of Hydrogen in California’s Transportation System

Status

Complete

Project Timeline

March 1, 2022 - June 30, 2023

Principal Investigator

Scott Samuelsen

Project Team

Jeff Reed

Sponsor, Program & Award Number

RIMI: RIMI-3N

Areas of Expertise

Zero-Emission Vehicles & Low-Carbon Fuels

Team Departmental Affiliation

Mechanical and Aerospace Engineering

Project Summary

Currently, hydrogen is used in California in only a few significant applications, with refining being the most dominant. However, hydrogen has the potential to be a major zero-carbon energy carrier across many applications, including transportation. California’s current suite of policies supporting decarbonization tend to be technology neutral, which may not provide sufficient incentives for the hydrogen market to develop in a timely and optimal way. This series of policy briefs investigates the role of hydrogen in decarbonizing the transportation sector and other sectors in California. Collectively, the briefs provide an overview of i) how hydrogen could be used, and how much end-use demand potential there could be for different applications across transportation, buildings and industry; ii) the relative carbon intensity of hydrogen production pathways and the availability of biomass and biogas in California that could be applied to the production of low-CI hydrogen; and iii) the current costs of producing green hydrogen and how much green hydrogen could potentially be produced.

Related Publications

policy brief | Sep 2022

Can Green Hydrogen Be a Cost Competitive Transportation Fuel by 2030?

Read more
policy brief | Sep 2022

Potential Uses of Hydrogen in California’s Clean Energy Transition

Read more
policy brief | Sep 2022

Hydrogen Can Have a Much Lower Carbon Intensity than Fossil Fuels But This Largely Depends on How It Is Produced and Distributed

Read more

Pilot Study: Demonstrate Real-World Security Threats to Connected Automated Vehicles

Status

In Progress

Project Timeline

July 22, 2022 - June 30, 2023

Principal Investigator

Qi Alfred Chen

Project Team

Ningfei Wang

Sponsor, Program & Award Number

RIMI: RIMI-5G
(Also see the UC ITS page)

Areas of Expertise

Intelligent Transportation Systems, Emerging Technologies, & Big Data

Team Departmental Affiliation

Information and Computer Science

Project Summary

While connected and automated vehicles (CAVs) have the potential to transform communities and mobility, issues like security threats – which may compromise infrastructure operations or even pose safety risks to road users – present significant challenges to the real-world deployment and operation of such systems. This project will explore and demonstrate the real-world feasibility and exploitability of existing CAV security threats that have emerged from academic research. The project will help stakeholders understand how realistic such threats are in practice, thereby informing policymaking, risk management, and remediation strategy planning.

Enhanced Perception with Cooperation between Connected Automated Vehicles and Smart Infrastructure

Status

Complete

Project Timeline

September 2, 2022 - June 30, 2023

Principal Investigator

Qi Alfred Chen

Project Team

Yunpeng Luo

Sponsor, Program & Award Number

RIMI: RIMI-5H
(Also see the UC ITS page)

Areas of Expertise

Infrastructure Delivery, Operations, & Resilience Intelligent Transportation Systems, Emerging Technologies, & Big Data

Team Departmental Affiliation

Information and Computer Science

Project Summary

Technological and infrastructure solutions will be needed to facilitate the safe integration of connected and automated vehicles (CAVs) into the national highway systems. Smart infrastructure is one possible solution that utilizes advanced sensing, computing, and communication capabilities, particularly at key highway bottlenecks and safety hotspots. The proposed pilot project, Smart Infrastructure for Automated driving (SIA), will demonstrate how advanced infrastructure data can support operations of connected and automated driving systems and understand various practical challenges, such as system underperformance due to factors including, but not limited to, communication delays, sensor malfunction, and cyberattacks.

Related Publications

presentation | Jun 2023

Pilot Study: Smart Infrastructure for Automated Driving

Read more
policy brief | Feb 2025

How Cooperation Between Connected Automated Vehicles and Smart Infrastructure Can Improve Situational Awareness for Traffic Safety

Read more
research report | Jan 2024

Enhanced perception with cooperation between connected automated vehicles and smart infrastructure.

Read more

Assessing the Potential for Densification and Reduction of Vehicle Miles Traveled in Areas Without Rail

Status

Complete

Project Timeline

June 21, 2022 - October 31, 2023

Principal Investigator

Jae Hong Kim

Project Team

Doug Houston, Nicholas Marantz, Alex Okashita, Maxwell Cabello

Sponsor, Program & Award Number

RIMI: RIMI-4M

Areas of Expertise

Public Transit, Shared Mobility, & Active Transportation Travel Behavior, Land Use, & the Built Environment

Team Departmental Affiliation

Urban Planning and Public Policy

Project Summary

While transportation infrastructure and efficiency should inform where to build more housing, little is known about how housing allocation and development processes can be coordinated more systematically with transportation. To date, transportation-housing coordination has often relied on the densification of areas near rail transit stations, putting heavy burdens on these locations and their residents. Much less attention has been paid to how densification can be achieved in a more equitable manner by encompassing other sites. This research seeks to better understand equity issues and other challenges that may arise in pursuing transportation-informed densification. The research includes two components: 1) a scenario analysis of the potential impacts of SB 743 that highlights equity concerns, as well as difficulties in identifying low vehicle miles traveled locations, and 2) a qualitative, in-depth investigation, including interviews with policy experts, creators, implementers, and advocates that explore ways to achieve more inclusive densification of non-rail transit areas, which have long been neglected in the literature. Overall, the findings suggest that transportation-informed densification is a challenging process, and this is particularly true when it comes to implementation and inclusive place-making. More needs to be known about how densification can take place in a way that promotes diversity, equity, and inclusion rather than causing disproportionate impacts on disadvantaged communities and their residents.

Related Publications

research report | Sep 2024

Assessing the Potential for Densification and VMT Reduction in Areas without Rail Transit Access

Read more
policy brief | Sep 2024

What Challenges Can Arise from Coordinating Housing Development with Transportation?

Read more

How Shared Mobility Can Complement or Compete with Transit

Status

Complete

Project Timeline

June 27, 2022 - October 31, 2023

Principal Investigator

Michael HylandMichael Hyland

Sponsor, Program & Award Number

RIMI: RIMI-4B

Areas of Expertise

Public Transit, Shared Mobility, & Active Transportation

Team Departmental Affiliation

Civil and Environmental Engineering

Project Summary

While the COVID-19 pandemic caused ridership on public transit and shared mobility to drop precipitously and put severe strain on their finances and operations, all was far from well prior to the pandemic. Transit ridership had dropped across the state in the five years prior to the pandemic, despite increasing public investment. Furthermore, the relationship between shared mobility and public transit was often disputed, with some stakeholders claiming they complement each other and others arguing that they compete. This project focuses on various facets in the relationship between shared mobility and public transit, including: (1) circumstances by which microtransit and transportation network companies complement or compete with public transit, (2) how demand-responsive shared mobility services can fill in public transit service gaps in various contexts, and (3) how – in underserved rural and suburban areas that lack high-quality transit – electric vehicle carsharing can be deployed equitably and cost-effectively.

Related Publications

policy brief | May 2023

Transportation Network Companies Might Be Pulling Riders from Public Transit, but This Could Change

Read more
published journal article | Jan 2024

What Is the Connection? Understanding Shared Micromobility Links to Rail Public Transit Systems in Major California Cities
Sustainability

Read more
policy brief | Sep 2024

Communities Are Experimenting with Microtransit to Fill Critical Gaps in Public Transit Service – What Have We Learned so Far?

Read more
published journal article | Aug 2024

Environmental Impacts of Transportation Network Company (TNC)/Ride-Hailing Services: Evaluating Net Vehicle Miles Traveled and Greenhouse Gas Emission Impacts within San Francisco, Los Angeles, and Washington, D.C. Using Survey and Activity Data
Sustainability

Read more

Job Access, Agency Cost, and VMT Impacts of Offering Microtransit alongside Fixed-route Transit

Status

Complete

Project Timeline

March 1, 2022 - June 14, 2024

Principal Investigator

Michael HylandMichael Hyland

Project Team

Dingtong Yang, Ritun Saha

Sponsor, Program & Award Number

RIMI: RIMI-4I

Areas of Expertise

Public Transit, Shared Mobility, & Active Transportation

Team Departmental Affiliation

Civil and Environmental Engineering

Project Summary

Traditional transit systems that rely exclusively on fixed routes and fixed schedules struggle to provide high-quality service to transit-dependent travelers and to attract choice travelers in moderate- to low-density areas. This is especially true in areas where jobs, restaurants, and shopping are not clustered together. Moreover, it is expensive for transit agencies to run services in moderate- and low-density areas. Integrating traditional transit and the more flexible microtransit—multi-passenger transportation services that serve passengers using dynamically generated routes—has been touted as a means to attract riders to public transit, improve mobility and sustainable transportation outcomes, and provide better accessibility to more travelers. These integrated services also have the potential to reduce costs incurred by transit agencies and improve mobility equity in underserved communities. However, successful real-world examples of and guidelines for integrating traditional transit and microtransit are relatively limited. This project has two key objectives: (1) to develop network design and operational strategy guidelines for integrating microtransit and transitional transit in low- to moderate-density areas, and (2) to analyze the mobility, accessibility, and equity benefits of integrating transitional transit and microtransit statewide. The project will identify ways the state can support microtransit integration, blueprints transit agencies can use to implement microtransit, and metrics to track how well microtransit services are helping California achieve climate, equity, and mobility and accessibility goals.

Related Publications

policy brief | Aug 2024

Job Access, Agency Cost, and VMT Impacts of Offering Microtransit alongside Fixed-route Transit

Read more
policy brief | Aug 2024

Job Access, Agency Cost, and VMT Impacts of Offering Microtransit alongside Fixed-route Transit

Read more
Preprint Journal Article | Jan 2024

Flexible Agent-based Modeling Framework to Evaluate Integrated Microtransit and Fixed-route Transit Designs: Mode Choice, Supernetworks, and Fleet Simulation

Read more

California’s Zero-Emission Truck Goals and Policies: Implications for Small Drayage Fleets

Status

Complete

Project Timeline

April 1, 2022 - June 30, 2024

Principal Investigator

Stephen Ritchie

Project Team

Youngeun Bae, Craig Rindt

Sponsor, Program & Award Number

RIMI: RIMI-3E

Areas of Expertise

Freight, Logistics, & Supply Chain Zero-Emission Vehicles & Low-Carbon Fuels

Team Departmental Affiliation

Civil and Environmental Engineering

Project Summary

California has established aggressive goals to transition medium- and heavy-duty vehicle (HDV) fleets to zero-emission vehicles (ZEVs). There is limited understanding of how HDV fleets will respond to these goals and policies, and there is even greater uncertainty around how one segment of the HDV fleet population will manage: small fleets. Small fleets, including owner operators and small motor carriers such as those with 20 or fewer vehicles, tend to lack knowledge and understanding of state policy. Furthermore, they account for a considerable portion of the fleet population, over 65% in the California drayage industry. Consequently, disruptions to this segment that result from ZEV goals and policies would seriously impact overall freight operations. Therefore, it is critical to understand how small fleets, especially small drayage fleets, will respond to the policies and move to adopt ZEVs. No two small fleets are alike; they operate in diverse applications and have unique needs. For this reason, researchers will conduct either one-on-one interviews or focus groups with approximately 20 operators of small and drayage fleets. The qualitative research will explore vehicle adoption processes (e.g., leasing versus purchasing, or truck as a service), motivators and barriers to ZEV adoption, potential impact of policies (e.g., a mandate, or financial incentives) on purchase behavior, and labor issues or concerns. The findings will inform policy options that may ease these fleet operators’ concerns and facilitate ZEV adoption, thereby contributing to achieving California’s heavy-duty ZEV targets.

Related Publications

Preprint Journal Article | Jan 2025

Small and Large Fleet Perceptions on Zero-emission Trucks and Policies

Read more
conference paper | Jan 2025

Small and Large Fleet Perceptions on Zero-Emission Trucks and Policies
Proceedings, 104th Annual Meeting of the Transportation Research Board

Read more
policy brief | Jan 2025

Navigating the Shift: Critical Insights of California Fleet Operators into Zero-Emission Technologies

Read more
published journal article | Apr 2024

Fleet operator perspectives on alternative fuels for heavy-duty vehicles
Transport Policy

Read more

Pilot Study: Use of High-Resolution Satellite Data to Identify Truck Traffic On the Roads and Near Warehouses Across Multiple Regions in Southern California

Status

Complete

Project Timeline

July 22, 2022 - June 30, 2024

Principal Investigator

Jun Wu

Project Team

Xingwei Liu

Sponsor, Program & Award Number

RIMI: RIMI-5I
(Also see the UC ITS page)

Areas of Expertise

Freight, Logistics, & Supply Chain Intelligent Transportation Systems, Emerging Technologies, & Big Data

Team Departmental Affiliations

Computer Science, School of Public Health

Project Summary

Heavy-duty trucks produce more non-tailpipe emissions, diesel exhaust, and noise than smaller vehicles, so when they travel on surface streets near residents, they can contribute to air quality- and noise-related impacts in these communities. However, heavy-duty truck counts are only available on freeways and highways, making it difficult for communities to understand their risks and provide evidence for truck rerouting as cumulative impacts mount. This pilot project will use high resolution satellite imagery and machine learning methods to detect heavy-duty trucks on all streets in areas with a high density of warehouses in Southern California. The researchers will also examine population characteristics in relation to density of heavy-duty trucks and identify the subpopulations that are mostly affected.

Related Publications

policy brief | Mar 2025

New Insights from Satellite Data Show the Impact Trucks are Having on Communities in Southern California

Read more
published journal article | Jan 2024

A Deep-Learning Approach to Detect and Classify Heavy-Duty Trucks in Satellite Images
IEEE Transactions on Intelligent Transportation Systems

Read more

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