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17 Optimize clearance intervals. Tier I (higher priority): Install dynamic advance warning flashers. Change to Protected phasing, Work plans were developed for each of these. Note that this Change to Protected-permissive phasing, in effect includes six different treatments, since the first group Modify phasing and add left-turn lane, includes four treatments. Add left turn only, In addition to these six treatments, the following five treat- Lengthen left-turn lane, ments were identified as backups in case it was not possible to Dynamic advance warning flashers, evaluate any of the six high priority ones: Optimize clearance intervals, and Flashing yellow arrow. Implement Split phasing. Add left-turn lanes. Tier II (lower priority): Provide or improve right-turn channelization. Add signal heads. Convert signalized intersections to roundabouts, Converting signalized intersections to roundabouts. Right-turn channelization, Add signal heads, The work plan consisted of a plan for the following four Improving friction at approaches to intersections, activities: Changing fonts, and Change to Split phasing. Collecting in-depth installation data. Developing an experimental design for the treatments. After the interim meeting, the project team started compil- Collecting crash, roadway inventory, site characteristics. ing the necessary data for evaluating the treatments in Tier I. Conducting a rigorous evaluation of the strategies. The project team could not find sufficient data for some of the treatments in Tier I, and after discussing this issue with the panel, it was decided to include one of the treatments from Interim Meeting with NCHRP Panel Tier II (convert signalized intersections to roundabouts) for The prioritized list of strategies and the work plan were which there appeared to be a research need coupled with the discussed at the Interim Meeting in Washington, D.C., in availability of data for a substantial number of treatment sites. November 2007. At the meeting, the project team and the The following is the final list of treatments that were evaluated NCHRP Panel agreed on a set of Tier I treatments (higher pri- in this study: ority) and a set of Tier II treatments (lower priority) for the evaluation. At the meeting, it was agreed that funds would Install Dynamic Advanced Warning Flashers, probably not be available to address all the treatments in Tier I. Convert Signalized Intersections to Roundabouts, In addition, if data were not available to evaluate one or more of Change Clearance Intervals, the treatments in Tier I, treatments in Tier II could be included. Change Left-Turn Phasing, and The following is a list of treatments in Tier I and Tier II. Introduction of Flashing Yellow Arrow.