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NCHRP 3-74 Selection of Speed Reduction Treatments at High-Speed Intersections Abstract Page ii Abstract This project identified and evaluated treatments and developed guidelines for reducing vehicle speeds on approaches to high-speed intersections (approach speeds of 45 mph or greater). Phase I involved conducting a literature search and state agency survey to obtain information about speed reduction treatments currently being used throughout the nation, developing a testing plan for conducting treatment testing, and creating a framework for the research guidelines. Phase II involved conducting field testing of three types of treatments (transverse pavement markings, rumble strips, and dynamic warning signs) at ten sites in Oregon, Washington, and Texas, and developing a set of Guidelines for applying speed reduction treatments. The research focused on geometric design treatments and considered traffic signs and pavement markings on signalized, unsignalized, and roundabout intersections. The treatments investigated were: reduced lane width, visible shoulder treatments, speed tables, rumble strips, roadway environment, approach reverse curvature, roundabouts, splitter islands, wider longitudinal pavement markings, transverse pavement markings, and dynamic warning signs. Speed reduction treatments were investigated to determine their applicability, key features, speed effects, safety benefits, multimodal impacts, and maintenance issues. A survey of state highway agencies provided information about the types of speed reduction treatments that are currently being used and the agencies estimated effectiveness of each treatment. The research team coordinated with state agencies to identify candidate treatment testing sites and conduct a treatment selection and implementation process. Before-and-after testing was conducted using tape switches to estimate the effectiveness of each type of treatment installed. Transverse pavement markings were installed at five sites in Oregon. Dynamic warning signs were installed at two sites in Washington and Texas. Rumble strips were installed at three sites in Texas. As a final research product, the research team wrote the NCHRP Report 3-74: Guidelines for Selecting Speed Reduction Treatments at High Speed Intersections (ÂGuidelinesÂ) to assist roadway planners, designers, and operators as they consider and select appropriate speed reduction treatments at intersections located in high-speed environments. The application of these treatments most often applies to existing intersections that experience undesirably high speeds; however, the information is also relevant to new intersection designs. The Guidelines provide relevant information about the effects of speed, the conditions that may contribute to undesirably high speeds at intersection approaches, and the state of the practice related to speed reduction treatments used in the U.S. and abroad, including their effectiveness and implementation considerations. The Guidelines also provide insights on the relationship between speed and facility operations. The Guidelines provide users with information about speed, speed considerations at intersections, and the potential application of treatments to affect speed. Additional research is needed to fully understand the effects that speed reduction treatments and reduced speed may have on safety.
