This study aims to improve a previously-developed methodology for predicting the traffic impacts of mixed-use developments (MXDs). In 31 diverse metropolitan regions across the United States, we collected consistent regional household travel survey data and computed built environment characteristics-D variables-of MXDs. Multilevel modeling (MLM) was employed to predict the probability of trips captured internally within MXDs, walking on internal trips, and travel mode choice on external trips, by trip purpose. Larger, denser, mixed-use, and more walkable MXDs show a larger share of trips internally, compared with conventional suburban developments. Those MXDs with good access to transit, employment, and destinations also show higher levels of walking, biking, and transit shares on external trips, thus helping to reduce traffic impacts on the external road network. Perhaps the most impressive finding is that well-designed MXDs have walk shares of more than 50 percent on internal trips. A k-fold cross-validation supports the robustness of our analyses.

Several studies have rigorously documented the induced travel effect, in which added highway capacity leads to added vehicle travel. Despite the evidence, transportation planning practice does not fully account for this phenomenon, with the result that estimates of the potential congestion-reducing benefits of added highway capacity may be overstated and estimates of potential environmental impacts understated. In 2015, the California Department of Transportation (Caltrans) sponsored a review of applicable induced vehicle travel research that could inform transportation analysis guidance in response to new laws in California such as Senate Bill 743 (S.B. 743), which prohibits the use of vehicle level of service (LOS) and similar measures as the sole basis for determining significant transportation impacts under the California Environmental Quality Act. Instead, vehicle miles traveled was selected to replace LOS under S.B. 743, and along with the new metric there will be a requirement to account for induced travel effects in analysis of roadway capacity expansion projects. The Caltrans review revealed an inconsistent lexicon in academic research and among practitioners, questions about research applicability, limitations in the sensitivity of travel forecasting models, and confusion about the appropriate use of induced vehicle travel elasticities from research. This paper summarizes the Caltrans review and shares the findings to advance understanding of induced vehicle travel effects and suggest steps for additional research.

Current methods of traffic impact analysis, which rely on rates and adjustments from ITE, are believed to understate the traffic benefits of mixed-use developments (MXDs) and therefore to lead to higher exactions and development fees than necessary and to discourage otherwise desirable developments. The purpose of this study was to improve methodology for predicting the traffic impacts of MXDs. Standard protocols were used to identify and generate data sets for MXDs in 13 large and diverse metropolitan regions. Data from household travel surveys and geographic information system databases were pooled for these MXDs, and travel and built-environment variables were consistently defined across regions. Hierarchical modeling was used to estimate models for internal capture of trips within MXDs and for walking, biking, and transit use on external trips. MXDs with diverse activities on site were shown to capture a large share of trips internally, so that the traffic impacts of the MXDs were reduced relative to conventional suburban developments. Smaller MXDs in walkable areas with good transit access generated significant shares of walk, bike, and transit trips and thus also mitigated traffic impacts.

This guidebook contains methods and tools for practitioners to estimate bicycling and walking demand as part of regional-, corridor-, or project-level analyses. The methods are sensitive to key planning factors, including bicycle and pedestrian infrastructure, land use and urban design, topography, and sociodemographic characteristics. The planning tools presented in this guidebook include some entirely new methods as well as some existing methods found to have useful properties for particular applications. The tools take advantage of existing data and the capabilities present in GIS methods to create realistic measures of accessibility which are a critical determinant of bicycle, pedestrian, and even transit mode choice. The publication includes a CD-ROM (CRP-CD-148) containing a GIS Walk Accessibility Model, spreadsheets, and the contractor’s final report, which documents the research and tools that operationalize the methods described in the guidebook. The CD-ROM is also available for download from TRB’s website as an ISO image. The guidebook should be of value to transportation practitioners either directly interested in forecasting bicycling or walking activity levels or accounting for the impact of bicycle or pedestrian activity in support of broader transportation and land use planning issues.

This publication is a handbook designed to provide information on how to analyze on-road greenhouse gas (GHG) emissions at the state and regional level, and how to incorporate those analyses into transportation planning efforts. The handbook is intended to help state departments of transportation (DOTs) and metropolitan planning organizations (MPOs) understand the possible approaches, data sources, and step-by-step procedures for analyzing GHG emissions. It provides an overview of estimating GHG emissions in the planning process, and identifies and describes several key methodologies used to estimate emissions. It also provides a discussion of the strengths and weaknesses of each methodology, and includes a section designed to help users identify which methodology is best for their situation.

This book describes how specific modifications in patterns of land development could help reduce greenhouse exhaust gases from vehicles. The book is based on a thorough review of dozens of studies by leading researchers in urban planning. It finds that urban development is both a major contributor to climate change and an essential factor in conquering it. The authors argue the premise that one of the best methods of reducing vehicle travel is development that is compact and condensed in nature. Such development would construct places in which people can navigate from place to place without driving. This kind of development includes pedestrian friendly development and mixed use development. There is a developing demand for smaller lots and homes, and condominiums and townhouses nears jobs and activity centers, which are fueled by rising gasoline prices, shrinking households, lengthening work trip commuting, and changing demographics. Existing government regulations and policies reward automobile dependent and sprawling development. The book offers recommendations for making green neighborhoods more affordable and available.

This report documents the findings of Strategic Highway Research Program 2 (SHRP 2) Project C16, Effect of Smart Growth Policies on Travel Demand. The project will help practitioners in two ways to understand how smart growth impacts travel: first, through a synthesis of research, and second, through a user-friendly software tool, initially called Smart Growth Area Planning (SmartGAP) and recently renamed the Rapid Policy Assessment Tool (RPAT), that can be used to evaluate the impact of smart growth policies on regional travel demand. The software application offers a reliable tool that transportation and land use planners can apply to better understand how smart growth strategies can influence travel demand in their regions by capturing time-of-day effects. This capability can differentiate between smart growth benefits on both peak and nonpeak travel.

The motivation is to synthesize existing research and package it into an easy to use software tool that can be used by transportation and land use planners. The innovation in the project is that by combining multiple research sources, we are able to provide more comprehensive software that bridges the gap between regional agencies visioning processes and their transportation plans, which evaluate projects. This tool evaluates scenarios at a regional level with available data sources.

Current methods of traffic impact analysis, which rely on rates and adjustments from the Institute of Transportation Engineers, are believed to understate the traffic benefits of mixed-use developments (MXDs), leading to higher exactions and development fees than necessary and discouraging otherwise desirable developments. The purpose of this study is to create new methodology for more accurately predicting the traffic impacts of MXDs. Standard protocols were used to identify and generate data sets for MXDs in six large and diverse metropolitan regions. Data from household travel surveys and geographic information system (GIS) databases were pooled for these MXDs, and travel and built environmental variables were consistently defined across regions. Hierarchical modeling was used to estimate models for internal capture of trips within MXDs, walking and transit use on external trips, and trip length for external automobile trips. MXDs with diverse activities on-site are shown to capture a large share of trips internally, reducing their traffic impacts relative to conventional suburban developments. Smaller MXDs in walkable areas with good transit access generate significant shares of walk and transit trips, thus also mitigating traffic impacts. Centrally located MXDs, small and large, generate shorter vehicle trips, which reduces their impacts relative to outlying developments.

For climate stabilization, the United States (US) will need to cut its transportation carbon dioxide (CO2) emissions by 60%–80% by 2050. As we cannot accomplish this reduction through vehicle and fuel technology alone, the environmental and transportation communities are focusing on strategies to reduce growth in vehicle miles traveled (VMT), reversing recent trends. The majority of recent VMT growth is due, not to population growth, but to the effects of urban environment, such as increased auto ownership, longer trips, and driving alone. The US Department of Energy forecasts that driving will continue to increase at almost threefold the growth in population. Even under the most stringent vehicle and fuel standards, transportation-related CO2 emissions will be 40% above the target level. In response, climate-change legislation has been passed in California and is pending in other states and in the US Congress that places strict new requirements on mandated environmental impact documentation. One limitation on compliance has been the lack of a unified set of scientific information on the underlying relationships between development form and VMT generation. This article distills and reconciles various forms of prior research on the subject, producing a unified quantitative understanding of the mechanisms that relate urban development forms with VMT and CO2. The findings will help improve the insightfulness and accuracy of the next generation of environmental documents. The article provides results of research and planning studies from throughout the US that indicate the degree to which developments with higher densities, mix of uses, accessible destinations, and interconnected streets reduce vehicle trips and VMT. Sources include regional blueprint studies, as well as project-specific studies such as Atlanta's Atlantic Station development, whose predicted trip reduction was found to be so compelling that the development was deemed a transportation control measure and air quality benefit by the Environmental Protection Agency and Federal Highway Administration. The article identifies the emerging practices in transportation impact analysis for assessing the degree to which the characteristics of development can reduce VMT and carbon impacts. It presents the empirical evidence of how vehicle travel is affected by density, diversity, walkability, regional accessibility, and distance from transit. It also reviews tools that transportation planners and analysts have available to capture these effects, including simple elasticities and new trip generation rates under consideration by the Institute of Transportation Engineers.

With growing worldwide concern about global climate change, this article asks two critical questions: What reduction in vehicle‐miles traveled (VMT) is possible in the USA with compact development rather than continuing urban sprawl?; and What reduction in greenhouse gas emissions would accompany such a reduction in VMT? Based on four different planning literatures, the answer to the first question appears to be a 20–40% reduction in VMT for each increment of new development. The answer to the second question is a 7–10% reduction in total transport carbon dioxide emissions by the year 2050 under a plausible set of assumptions.

This study addresses the need for information and tools on land use-transportation relationships in California. Providing up-to-date, California-specific data allows decision-makers to more effectively consider the potential benefits and impacts of choices regarding transportation infrastructure and land use planning in a consistent and supportable way. The project team obtained and reported detailed built environment and travel survey data for over 200,000 specific locations in California. Results are incorporated into scenario/sketch planning tools (in both GIS and spreadsheet formats) and travel demand forecasting models.