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.
An increasing number of jurisdictions across the United States are exploring level of service (LOS) for multiple travel modes, in part as a result of the release of the Highway Capacity Manual 2010 (HCM 2010), as well as an increased focus on complete streets policies. One of the most important questions being asked by these jurisdictions is whether new multimodal LOS methods are sensitive enough to inform transportation investments, mitigate impacts, and prioritize future projects. For this paper, transportation professionals (public, private, and academic) were surveyed about the inputs believed to have the greatest effect on pedestrian, bicycle, transit, and auto LOS or the inputs thought to have the greatest likelihood of being changed (e.g., to mitigate an impact or to improve existing conditions). Sensitivity testing was then performed at locations in four cities to measure how the HCM 2010 multimodal LOS scores responded as these inputs were incrementally increased or decreased. Although many inputs performed as expected, the testing also found model responses that were of a questionable direction or magnitude. The results of this study are informative for agencies that are considering adopting the HCM 2010 multimodal LOS for mitigation, resource allocation, and strategic decision making. The results also provide a starting point for additional research needed to enhance multimodal LOS methods.
Widespread application of traditional performance metrics such as vehicle level of service has resulted in transportation networks that are often suited for only one mode of transportation to the detriment of others. Moreover, the continued investment in capacity expansion intended to meet level of service expectations increases financial burdens on transportation agencies for the capital, operating, and maintenance costs of these facilities, without regard to whether those resources are being used efficiently. Shifting focus to alternative and more comprehensive performance metrics can result in a more economical approach to transportation infrastructure, allowing communities to understand what investment combinations provide the best bang for the buck. Innovative performance metrics also allow communities to consider priorities beyond level of service, and design infrastructure accordingly. The Wasatch Front Central Corridor Study, undertaken in the Salt Lake City metropolitan area, is one example of a regional application of efficiency-focused performance metrics such as person throughput, seat utilization, benefit–cost ratio, access to employment, and economic impacts. Further research opportunities could include development of best practices to standardize benefit–cost analysis for transportation projects, other methods of evaluating overall system efficiency, and the role of parking policy and land use change in maximizing use of transportation resources.
Bus rapid transit (BRT) is gaining greater interest by transportation planners and decision makers in the United States because of concerns about growing traffic congestion and a desire for improved environmental quality and sustainable land use development patterns. To help planners and decision makers, FTA developed the BRT implementation guidelines based on the 26 case studies located in North America, Australia, Europe, and South America. The FTA guidelines serve as a valuable source for the basic BRT concepts including the main system components and their types, general planning principles, and general design guidelines. However, the detailed implementation process, such as BRT station selection and route alignment determination, as one of the primary and practical concerns by transportation planners and decision makers, has not been studied in detail. A conceptual planning approach used to quickly evaluate potential BRT stations and alignments based on a case study in Placer County, California, is presented. The approach relies on land use development criteria and an analogous station-matching process to determine an initial range of potential ridership for future stations based on existing stations with similar land use development patterns. This information is combined to help gauge station feasibility and alignment options. The criteria used in this planning process were developed from a comprehensive literature review of the relationship between land use development and transit station ridership, as well as a unique database of transit ridership and land use development intensity for more than 80 existing transit stations in the San Francisco Bay Area and the Sacramento, California, region.
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