published journal article

How do they get by without cars? An analysis of travel characteristics of carless households in California

Abstract

In spite of their substantial number in the U.S., our understanding of the travel behavior of households who do not own motor vehicles (labeled “carless” herein) is sketchy. The goal of this paper is to start filling this gap for California. We perform parametric and non-parametric tests to analyze trip data from the 2012 California Household Travel Survey (CHTS) after classifying carless households as voluntarily carless, involuntarily carless, or unclassifiable based on a CHTS question that inquires why a carless household does not own any motor vehicle. We find substantial differences between our different categories of carless households. Compared to their voluntarily carless peers, involuntarily carless households travel less frequently, their trips are longer and they take more time, partly because their environment is not as well adapted to their needs. They also walk/bike less, depend more on transit, and when they travel by motor vehicle, occupancy is typically higher. Their median travel time is longer, but remarkably, it is similar for voluntarily carless and motorized households. Overall, involuntarily carless households are less mobile, which may contribute to a more isolated lifestyle with a lower degree of well-being. Compared to motorized households, carless households rely a lot less on motor vehicles and much more on transit, walking, and biking. They also take less than half as many trips and their median trip distance is less than half as short. This study is a first step toward better understanding the transportation patterns of carless households.

preprint journal article

Predicting Vehicular Emissions by Converging Direct Measurements and Mobility Science

Abstract

Vehicle emissions pose a significant challenge for cities worldwide, yet a comprehensive analysis of the relationship between mobility metrics and total vehicle emissions at a high resolution remains elusive. In this work, we introduce the Mobile Data Emission System (MODES), a pioneering framework that integrates various sources of individual mobility data on an unprecedented scale. Our model is validated with direct measurements from a network of high-density sensors analyzed before and during the COVID-19 pandemic shelter-in-place orders. MODES is used as a laboratory for scaling analysis. Informed by individual trips, we estimate the traffic CO2 emissions at a metropolitan scale with a combination of 3 accessible metrics: vehicle kilometers traveled (VKT), congestion levels, and vehicle efficiency. Given their ranges of variation, VKT has the greatest role in amplifying vehicular emissions up to 500%, followed by vehicle efficiency that would range from 20% to 300% of the average passenger combustion vehicles. In comparison, congestion amplifies vehicle emissions of individual travels by up to 50%. We confirm that cities in the Bay Area with high population density are consistently characterized by low per-person VKT. Nevertheless, high population density comes at the expense of increased congestion. Since VKT is the governing factor, overall densifying of the urban landscape reduces transportation emissions despite its impacts on congestion.

published journal article

Mobile Phone Location Data for Disasters: A Review from Natural Hazards and Epidemics

Abstract

Rapid urbanization and climate change trends, intertwined with complex interactions of various social, economic, and political factors, have resulted in an increase in the frequency and intensity of disaster events. While regions around the world face urgent demands to prepare for, respond to, and recover from such disasters, large-scale location data collected from mobile phone devices have opened up novel approaches to tackle these challenges. Mobile phone location data have enabled us to observe, estimate, and model human mobility dynamics at an unprecedented spatio-temporal granularity and scale. The COVID-19 pandemic, in particular, has spurred the use of mobile phone location data for pandemic and disaster management. However, there is a lack of a comprehensive review that synthesizes the last decade of work and case studies leveraging mobile phone location data for response to and recovery from natural hazards and epidemics. We address this gap by summarizing the existing work and point to promising areas and future challenges for using mobile phone location data to support disaster response and recovery.

published journal article

Bicycles and Micromobility for Disaster Response and Recovery

Abstract

Bicycles and other forms of micromobility have been anecdotally used in past disasters to help save lives and improve community recovery. However, research and practice are scarce on this resilient transportation strategy, which limits its usefulness and possible benefits. To fill this gap, our paper investigates the potential role of bicycles and micromobility in facilitating (or limiting) disaster response and recovery. Given the lack of exploration on the topic, the research team convened an online workshop where we conducted brainstorming and focus group discussions with disaster experts from various government agencies, not-for-profit organizations, academia, and policy groups. The team presents a synthesis of that discussion, along with a review of the existing literature. The paper concludes there is strong potential for bicycles and micromobility for different disaster phases, hazard types, and groups of people. However, multiple barriers exist related to implementation and safety, suggesting a need for future research and policy in the transportation and emergency management fields and practices.

published journal article

Planning for Electric Vehicle Needs by Coupling Charging Profiles with Urban Mobility

Abstract

The rising adoption of plug-in electric vehicles (PEVs) leads to the alignment of their electricity and their mobility demands. Therefore, transportation and power infrastructures are becoming increasingly interdependent. In this work, weuncoverpatternsofPEVmobilitybyintegratingforthefirsttimetwo unique data sets: (i) mobile phone activity of 1.39 million Bay Area residents and (ii) charging activity of PEVs in 580,000 sessions obtained in the same region. We present a method to estimate the individual mobility of PEV drivers at fine temporal and spatial resolution integrating survey data with mobile phone data and income information obtained from the census. Thereupon, we recommend changes in PEV charging times of commuters at their work stations that take into account individual travel needs and shave the pronounced peak in power demand. Informed by the tariff of electricity, we calculate the monetary gains to incentivize the adoption of the recommendations. These results open avenues for planning for the future of coupled transportation and electricity needs using personalized data.

technical brief

Best Practice for Pavement: Unpaving to Create Affordable, Safe, Smooth Gravel Roads

Abstract

Many rural county road networks were created at a time when funding was greater and rural populations were often larger than they are today. Eventually, surface treatments such as chip seals or thin asphalt were applied to many of these gravel roads to provide them with an allweather surface. These treated surfaces were also desirable because conventional gravel roads are dusty, often develop washboarding quickly, and have high rates of gravel loss—which result in unsafe and uncomfortable conditions and greater damage to vehicles and crops.

technical brief

Best Practice for Pavement: Writing Concrete Specs for Durability and Sustainability

Abstract

Concrete mixes for all applications chiefly rely on Portland cement (ASTM C150) to give them strength and durability. For this reason, specifications in traditional concrete mix designs were written to ensure that they used enough cement to meet strength and durability requirements, and often included minimum cement content requirements to be sure the buyer got their money’s worth.Unfortunately, research and practice have shown that this approach can worsen performance and carry the greatest environmental impacts—while still costing more money. 

technical brief

Best Practice for Pavement: Writing and Enforcing Specs for Asphalt Compaction

Abstract

Most local agencies have asphalt compaction specifications in their contracts as well as inspectors who check the contractors’ operations. But following specifications that tell a contractor how to do the compaction, called method specifications, typically leads to very poor results because even the most experienced inspector or contractor cannot tell how well or poorly compacted the asphalt is by just watching the compacting operation or looking at the completed surface. In these situations the possible life can be cut in half. On the other hand, a city or county can use quantitative quality control/quality assurance (QC/QA) specifications that call for measurement of compaction to determine the extent to which the contractor has met the compaction requirements.

published journal article

Regulating TNCs: Should Uber and Lyft set their own rules?

Abstract

We evaluate the impact of three proposed regulations of transportation network companies (TNCs) like Uber, Lyft and Didi: (1) A minimum wage for drivers, (2) a cap on the number of drivers or vehicles, and (3) a per-trip congestion tax. The impact is assessed using a queuing theoretic equilibrium model which incorporates the stochastic dynamics of the app-based ride-hailing matching platform, the ride prices and driver wages established by the platform, and the incentives of passengers and drivers. We show that a floor placed under driver earnings can push the ride-hailing platform to hire more drivers and offer more rides, at the same time that passengers enjoy faster rides and lower total cost, while platform rents are reduced. Contrary to standard competitive labor market theory, enforcing a minimum wage for drivers benefits both drivers and passengers, and promotes the efficiency of the entire system. This surprising outcome holds for almost all model parameters, and it occurs because the wage floor curbs TNC labor market power. In contrast to a wage floor, imposing a cap on the number of vehicles hurts drivers, because the platform reaps all the benefits of limiting supply. The congestion tax has the expected impact: fares increase, wages and platform revenue decrease. We also construct variants of the model to briefly discuss platform subsidy, platform competition, and autonomous vehicles.

research report

Policies to Improve Transportation Sustainability, Accessibility, and Housing Affordability in the State of California

Abstract

This report presents an analytical review of empirical research on the interactions between housing availability and production, travel behavior, accessibility, land use policies, and transportation policies. It identifies lessons from this review for California state legislative efforts to improve housing and transportation linkages, and to increase both transportation sustainability and housing affordability. Relevant California state efforts include legislation to influence parking standards; to require up-zoning near transit stations; to influence regional housing and transportation planning goals; and to change environmental review to focus on reducing vehicle miles traveled instead of accommodating road traffic.