This report analyses traffic impacts from the 2015 implementation of a pilot “road diet” on Lincoln Avenue, in the City of San Jose, California. Road diets are street reconfiguration projects that reduce the number of travel lanes in a street, most often converting a four-lane, undivided roadway to a three-lane roadway with two through-travel lanes and a two-way center left-turn lane. For the study, we compared data on traffic volumes and speeds from before and after the road diet was implemented, looking not only at the impacts on the road diet segment itself, but also on surrounding streets that might have been impacted by traffic diverted off the road diet segment. Our analysis also compares impacts over different time periods: all day, during the am and pm peak periods, and by hour of the day. When road diets work well, they are a relatively low-cost measure that improves safety, multi-modal accessibility, and quality of life in the neighbourhood. Specific goals for many road diet projects include fewer crashes, improved facilities for pedestrians (who have to cross fewer lanes of traffic), and improved facilities for bicyclists (if new bicycle lanes are installed in the space freed up from the eliminated traffic lane). Road diets are not without concerns, however. Travel times may increase along the slimmed road. Also, depending on the configuration of side streets, some traffic may switch to nearby side roads, thus increasing traffic volumes and speeds on roads potentially less suited to handle such traffic. Despite growing interest in road diets among transportation planners and community members, there is limited empirical evidence on the effects of these roadway conversions. While some local governments and researchers have conducted evaluations on road diets, these vary widely in the metrics they evaluate and the quality of data collected.1 For example, a number of studies evaluate only safety outcomes. Also, many studies look only at the impact on the road diet segment, omitting impacts on neighbourhood streets. (For helpful summaries of the factors analysed in many of the older studies, see Huang, et al, 2003 and Lyles, et al, 2012.2) Further, many road diet evaluations are not formally published and archived in a permanent, accessible location, making them difficult to access. In short, transportation planners have limited high-quality resources to review when they want to understand how road diets perform in practice. This report contributes to the small but growing body of published road diet literature by analysing the traffic effects of a road diet in San José, California, focusing on neighbourhood-wide traffic volume and speed impacts. In the spring of 2015, the City of San José implemented a road diet pilot program along a one-mile stretch of Lincoln Avenue in the Willow Glen neighbourhood of central San José. Lincoln runs through a predominantly residential neighbourhood with a small neighbourhood business district. The street, a four-lane, undivided roadway, has become a popular route for commuters avoiding the more congested nearby freeways and expressways. Close to 20,000 vehicles per day travel along this route, often above posted speed limits, posing a risk to pedestrians and bicyclists. This study analyses before-and-after traffic volume and speed data that was collected at 45 different locations on Lincoln Avenue, intersecting streets, and nearby parallel streets. The City of San Jose collected the data in February 2015, several weeks prior to the beginning of the road diet pilot, and later in February 2016, one year after the project began. The traffic data was used to answer the following research questions specific to the Lincoln Avenue road diet: 1. How did the road diet impact all-day counts of traffic volumes and speeders for each street type? The street types analysed were Lincoln Avenue road diet locations, Lincoln Avenue locations outside the road diet, major streets, and neighbourhood streets. 2. How did the road diet impacts vary by street type when looking at all-day counts versus data for peak hours and data by hour of the day? 3. Did individual locations see speeding and volume increases noticeably greater than the street-type averages, such that additional traffic calming measures might be warranted? An additional objective of the research project was to recommend best practices in designing road diet evaluations that look at speeding and traffic volume impacts. As part of the City of San Jose’s analysis of the Lincoln Avenue road diet, a detailed report was prepared (City of San Jose, 2016). The current MTI report provides an independent third-party review of the traffic volume and speed data collected, as well as more detailed analysis of the hourly traffic patterns. The remainder of the report is organized as follows: Chapter 2 describes the history of the Lincoln Avenue road diet effort, Chapter 3 explains the study methods, and Chapter 4 presents detailed study findings. In conclusion, Chapter 5 summarizes the findings and offers recommendations for designing future road diet evaluations. Appendices present detailed data about each of the 45 data collection locations. (Author/publisher)
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