policy brief

Traffic Trumps All: Examining the Effect of Traffic Impact Analyses on Urban Housing

Abstract

Traffic impact analyses (TIA) are widely used by local governments to assess the traffic impacts of proposed land use developments. TIAs are often measured in terms of expected changes to traffic flows through nearby intersections using a metric called “level of service” (LOS). This process tends to be biased against higher-density developments in urban areas where traffic is already congested and travel alternatives are plentiful. Researchers have found that the projected traffic impacts of developments in already built-up areas tend to be overestimated, which leads to higher traffic impact fees and related costs associated with the TIA process. Often, local residents use such analyses as evidence to oppose new developments on traffic grounds. The result is that TIAs can help discourage new housing production in built-up areas where demand is greatest, which likely exacerbates the housing affordability crises in places like California.In essence, the logic of TIAs is that the human activities and the built environment in cities should vary to keep nearby traffic flowing smoothly. The fundamental problem with LOS-based TIAs is that they measure vehicle mobility and not the more fundamental goals of economic and social accessibility. While California has been a national leader in changing the metric by which traffic impacts are evaluated under the California Environmental Quality Act, from LOS to vehicle miles of travel effects, LOS-based analyses of development proposals are still typically conducted by local governments — even in the Golden State.This study reviewed and synthesized research on TIAs and their effects on land use planning, and found that mobility-focused transportation planning likely contributes to the housing affordability crisis plaguing many places. Further, research shows that gradually shifting away from mobility-centered metrics, like LOS, and toward more accessibility-centered evaluation tools, will enable more comprehensive assessments of development impacts, which could help ease California’s housing affordability crisis.

policy brief

Environmental Reviews Fail to Accurately Analyze Induced Vehicle Travel from Highway Expansion Projects

Publication Date

January 1, 2021

Author(s)

Abstract

Induced travel is a well-documented effect in which expanding highway capacity increases the average travel speed on the highway, which in turn reduces the perceived “cost” of driving and thereby induces more driving. This increase in vehicle miles traveled (VMT) increases congestion (often back to pre-expansion levels) and air pollutant emissions, reducing or eliminating the purported benefits of the expansion. Yet highway expansion projects continue to be proposed across California, often using congestion relief—and sometimes greenhouse gas reductions—as a justification for adding lanes. These rosy projections about the benefits of highway expansion projects indicate that the induced travel effect is often not fully accounted for in travel demand models or in the projects’ environmental review process.With this problem in mind, researchers at the University of California, Davis developed an online tool to help agencies estimate the VMT induced annually by adding lanes to major roadways in California’s urbanized counties. The researchers also applied the calculator to estimate the vehicle travel induced by five highway expansion projects in California that had gone through environmental review within the past 12 years. They then compared their estimates with the induced travel analysis completed for the projects’ actual environmental impact assessments. This policy brief summarizes findings from that research, along with policy implications.View the NCST Project Webpage

Pandemic-related Shifts in Work, Travel, and Transit Use: Implications for Public Policy

Status

In Progress

Project Timeline

July 1, 2022 - October 31, 2023

Principal Investigator

Project Team

Project Summary

While the COVID-19 pandemic dramatically affected travel and transportation systems, driving has largely returned to pre-pandemic levels, even as a significantly larger share of the workforce works from home full- or part-time. However, there have been significant changes in the timing and patterns of car travel since before the pandemic. Moreover, public transit systems have been especially hard hit, and riders have proven slow to return. While transit use by those unable to drive (who are more likely poor, immigrants, people of color, and/or disabled) has substantially recovered since the shutdowns in the spring of 2020, daily commuting to and from major employment centers collapsed and is just beginning to recover. The shifts in motor vehicle travel and the more dramatic changes in public transit use are both likely related to workplace changes, as the number of remote and hybrid workers has increased. The longer-term effects of the pandemic on travel remain uncertain, as do the appropriate policy responses to changing traffic patterns broadly, and to depressed transit ridership specifically. Public transit is a key transportation pillar of California’s climate and equity goals, which will be harder to meet with driving up and transit riding down.

To examine late-pandemic shifts in trip timing, this project analyzed smartphone location data to track the location and timing of vehicle trips on streets and highways in Greater Los Angeles. Specifically, this study compares the average number of trip origins for each hour of the day in all 10,783 census block groups in Imperial, Los Angeles, Orange, Riverside, San Bernardino, and Ventura counties in October 2019 and October 2021. The project then estimated a series of statistical models to examine the factors associated with both the levels of and changes in the timing of afternoon peak-period trip-making. Following an initial analysis, this project focused on shifts in early (12 p.m.–3:59 p.m.) and late (4 p.m.–7:59 p.m.) afternoon trip-making between fall 2019 and fall 2021. The primary data comes from StreetLight, a location analytics company that provides travel datasets collected from mobile phones, GPS receivers, and other network-enabled devices. This data was augmented with information from the U.S. Census, Longitudinal Employer-Household Dynamics Origin and Destination Employment Statistics (LODES), and the U.S. Department of Education.

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

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.

other

Press Release: Not Going Out is the “New Normal” Post-Covid, Say Experts

research report

Is Micromobility Being Used in Place of Car Trips in Daily Travel (or “Trip Chains”)?

Abstract

To understand the extent to which micromobility services such as bike-share and scooter-share are enabling car-lightlifestyles by replacing driving, this report explores the trip-chaining patterns of micromobility users. The research team used travel diary data collected from micromobility users in 48 cities across the US. Findings from their analysis shows that a considerable portion of car owners are leaving their cars at home when using micromobility. This suggests that, for a subset of users, micromobility can form part of a car-free or car-light day of travel, despite having a car available. In addition, micromobility services are supportive of complex trip chains that include both work and non-work trips with reduced reliance on cars. The use of micromobility services tends to entirely replace shorter car trips on shorter-length trip chains.

Our Experts

Nicholas Marantz

Associate Professor, Department of Urban Planning and Public Policy, UC Irvine

Recent Projects

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Research Team:

Jae Hong Kim (lead), Jesus M. Barajas, Douglas Houston, Nicholas Marantz

UC Campus(es):

UC Irvine, UC Davis

Research Team:

Nicholas Marantz (lead), Jae Hong Kim, Douglas Houston, Moira O'Neill, Eric Biber

UC Campus(es):

UC Irvine

Research Team:

Nicholas Marantz (lead), Douglas Houston

UC Campus(es):

UC Irvine

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Research Team:

Michael Manville (lead)

UC Campus(es):

UCLA

Research Team:

Paavo Monkkonen (lead), Shane Phillips, Michael Manville

UC Campus(es):

UCLA

Research Team:

Michael Manville (lead), Gregory Pierce

UC Campus(es):

UCLA

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Research Team:

Pei (Peggy) Wang (lead), Rui Lin

UC Campus(es):

UC Berkeley

Research Team:

Pei (Peggy) Wang (lead), Rui Lin

UC Campus(es):

UC Berkeley

Research Team:

Pei (Peggy) Wang (lead)

UC Campus(es):

UC Berkeley

Our Experts

Recent Projects

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Research Team:

Jane Macfarlane (lead), Joan Walker

UC Campus(es):

UC Berkeley

Research Team:

Joan Walker (lead), Johanna Zmud

UC Campus(es):

UC Berkeley