Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections: Supplement to NCHRP Report 613 (2008)

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NCHRP 3-74 Chapter 1 Selection of Speed Reduction Treatments at High-Speed Intersections Introduction Page 1-1 1 Introduction 1.1 PROJECT OVERVIEW The purpose of this research project was to identify and evaluate treatments and develop a set of guidelines that can be used by transportation professionals for reducing vehicle operating speeds on approaches to high-speed intersections. The research focused on geometric design treatments and also considered traffic signs and pavement markings. The treatments focused on signalized and unsignalized intersections with approach speeds of 45 mph or greater. The products that resulted from this research are a prioritized list of potential speed reduction treatments for intersection approaches that might be used and a menu of different applications (e.g., new design versus retrofit, high crash locations, and crash locations exhibiting specific crash types) and a set of guidelines on the application of these treatments as design features for newly constructed intersections, and mitigation treatments for existing intersections, including the results of a testing program that determines treatment effectiveness. To provide an appropriate technical basis for the guidelines, the research team developed and conducted a treatment testing program at ten intersections in Oregon, Washington, and Texas. The team assessed the most appropriate methods to evaluate those treatments to determine their effectiveness in reducing speeds on intersection approaches and chose to use actual field testing in cooperation with state highway agencies. Once potential treatment sites were identified, the team worked with the state and county agencies to identify appropriate treatment installations, develop a treatment location layout, design the treatment and layout the data collection plan. 1.2 THE PURPOSE OF THIS FINAL REPORT This Final Report is to document the entire research effort including the research methodology, findings, and suggested future research. This report summarizes the literature review findings, state agency survey, testing plan, treatment installation, data collection plan, testing results, and the development of the Guidelines. A key finding is that, although speed has been studied frequently, intersection-specific information about speed, the factors that affect speed, potential speed reduction treatments, and specific applications of these treatments is limited. Based on these findings, the research team has developed Guidelines for selecting treatments and potential testing plan that could be applied to potential speed reduction treatments. The Guidelines is being published as a separate document than this Final Report. Therefore, this report provides an overview of the Guidelines development and information included in each section. 1.3 SUMMARY OF PHASE I RESEARCH ACTIVITIES The research team conducted a literature search on an extensive list of potential speed reduction treatments. The search included national and university online catalogues and databases [e.g. Transportation Research Board (TRIS), University of California, Berkeley (Melvyl), and Northwestern University (NuCAT)]; federal agencies (FHWA, NHTSA, and the Access Board); transportation organizations (ITE); and general search engines (Google and Yahoo). In addition to these formal searches, our team members contacted numerous colleagues and professionals to obtain information or leads on new sources. Key words used during the literature search were

Chapter 1 NCHRP 3-74 Introduction Selection of Speed Reduction Treatments at High-Speed Intersections Page 1-2 identified from the Research Plan and were tried in a variety of alternative forms to retrieve as many potential information sources as possible. Examples of key words include “speed reduction treatments,” “high-speed intersections,” and “intersection safety.” Abstracts were collected for each document that appeared to be relevant to the project objectives. A list of these documents is provided in Appendix A. To help prioritize the documents and identify which documents to obtain, a list of criteria was developed to screen the collected abstracts. The criteria summarized the critical concepts and general information outlined in each task of the Amplified Research Plan. A source that did not provide insight on the criteria was screened out as not having specific relevance to the research goals. The criteria used for screening the abstracts are shown in Appendix B. The following represents a summary of the information trends that have resulted from this review: • There is a significant amount of information associated with speed characteristics and factors that affect speed, but little quantifiable data on those factors. • There is very little information specific to speed at intersections; most information relates to roadway segment locations. • There is extensive information about safety but little direct correlation between speed and safety, especially for intersections. • There are a variety of potential speed reduction treatments, but very little quantifiable data about their effectiveness. There are numerous documents on understanding speed issues (design, operating, and posted). There is extensive information and interest about speed reduction (traffic calming and construction work zones). However, much of the information relates to segment or roadway volumes. Relatively little published research or testing results have been found for speed reduction treatments specifically for intersection approaches. The quantity and quality of the information available and collected for each treatment varied. For example, the team collected substantial information on rumble strips, speed tables, roundabouts, transverse pavement markings, reduced lane width, and dynamic warning signs. However, limited information was found regarding visible shoulder treatments, roadway environment, splitter islands, approach reverse curvature, and wider longitudinal pavement markings. The research team prepared and distributed a survey to a variety of highway agencies. The survey solicited specific suggestions on potential treatments, and requested expressions of interest in participating in the treatment evaluation process later in the project. Multiple ways to respond were provided to maximize the number of responses. Hard copies of the survey were distributed on October 15, 2004. Emails were distributed on October 16, 2004. The research team compiled and evaluated the results from the state agency survey. A total of 36 responses were received, out of the 50 questionnaires that were mailed, for a response rate of

NCHRP 3-74 Chapter 1 Selection of Speed Reduction Treatments at High-Speed Intersections Introduction Page 1-3 72 percent. The highway agency responses to each question in the survey were summarized to determine the types of speed reduction treatments that are currently being used and the agencies estimated effectiveness of each treatment. No new information regarding speed reduction treatments was uncovered from the state highway agency survey; however, several agencies expressed an interest in this study and reaffirmed the necessity of such research. The survey was designed to allow agencies to share their input about what speed reduction treatments they felt were most important to be evaluated when determining a level of effectiveness. The survey responses indicated that dynamic-warning speed activated signs and rumble strips in the traveled way are the most important treatments to be tested for effectiveness. The team also identified agencies interested in testing potential treatments during Phase II of this project. The State Agency Survey section of the Interim Report presents the treatments that are being sought for study along with which states have indicated a willingness to cooperate in such a study. These results were used to prioritize treatments for the testing plan. The team plans to follow-up with these state agencies to obtain additional details about their implementation plans and begin coordination for testing. Another information trend that has been investigated by the research team is the feasibility of measuring safety effects of speed reduction treatments. Overall, it is difficult to measure the safety effects; safety evaluations can potentially last many years to adequately assess the short, mid, and long-term effects of a treatment. Therefore, the research team’s focus was to develop a testing plan that will determine which treatments reduce vehicle speeds and quantify the expected amount of speed reduction, although it is widely agreed in concept that reducing operating speeds of vehicles at intersections should reduce the severity of crashes. Therefore, a treatment that does not prove be effective at reducing speeds would not be carried forward to a safety evaluation. Further, if a treatment was found to be ineffective at reducing speeds (although there may be other benefits), the profession would benefit by having this documented. 1.4 SUMMARY OF PHASE II RESEARCH ACTIVITIES One of the primary outcomes of the Phase I activities was a testing plan and a list of four treatments that the research team recommended for testing. These treatments included: rumble strips, transverse pavement markings, dynamic warning signs, and approach curvature. A “before-and-after” approach was used to evaluate the effect each treatment has on speed. Speeds were measured at selected locations on the intersection approach before and after the subject treatments were implemented. The “after” measurements were taken a minimum of three months following a treatment’s installation. This acclimation period allowed the novelty of the treatments to subside and motorists to adjust to their presence. This research project funded the treatment tests; however, the cost to install the treatment was the responsibility of the state or county agency involved. Therefore, the research team contacted various individuals and groups to identify states or counties that were interested in participating in the research and/or had plans to install a speed reduction treatment. As multiple candidate sites were identified in states throughout the nation, the team underwent a site screening process to refine the list of potential sites and screen sites that did not seem to meet the research objectives.

Chapter 1 NCHRP 3-74 Introduction Selection of Speed Reduction Treatments at High-Speed Intersections Page 1-4 The final list of candidate sites included ten intersections in Oregon, Washington, and Texas. The Oregon sites installed transverse pavement markings at all five sites, the Washington site installed a dynamic warning sign and the Texas sites installed rumble strips at three sites and a dynamic warning sign at one site. Approach curvature was prohibitive as a treatment because it requires construction and is more costly than other treatments, based on the need for roadway widening and partial roadway reconstruction in some cases. After the treatment selection process was completed and a treatment was identified for each site, the team used aerial images and the existing roadway and intersection features to identify appropriate locations for the treatment installations. For the majority of the sites, treatment schematics were developed to illustrate the appropriate treatment implementation locations. In addition to the treatment layout schematics, the research team also designed some of the treatments for specific sites. In conjunction with the treatment selection and layouts, the research team also investigated various data collection equipment and procedures to determine the most comprehensive and effective means of collecting speed data during field testing. The methodologies that were investigated are: Hi-Star devices, tape switches, and video photography. Based on conversations with many other researchers and the team’s own investigation, tape switches were ultimately determined to be the most appropriate device for the speed data collection. As part of the Phase I activities, the research team developed a data collection scheme with four data collection points on each subject intersection approach. Based on this data collection scheme, the research team prepared data collection plans for each of the sites, identifying the appropriate locations to collect speed data during “before” and “after” data collection. Before-and-after testing was conducted from April 2006 to March 2007. Once the before testing was completed, the research team coordinated with each agency to install treatments at each of the testing sites. Due to the three-month acclimation period, installing the treatments in a timely manner was a high priority to meet the overall project timeline. Data analysis and summarization of the testing results occurred after each of the testing sites was completed. In addition, all of the testing results and data analysis was refined after the completion of testing at all sites. Three types of analyses were conducted: • Analysis by Location – to determine the speed reduction observed at each data collection location (i.e., at each of the four locations along an intersection approach) • Analysis by Intersection Approach – to determine the overall speed reduction observed along an intersection approach • Analysis by Treatment Type – to quantify the effect of each treatment across all intersection approaches at which it was installed Overall conclusions from the testing results include:

NCHRP 3-74 Chapter 1 Selection of Speed Reduction Treatments at High-Speed Intersections Introduction Page 1-5 • All three treatment types may reduce speeds on high-speed intersection approaches; however, speed reduction is likely to be minimal (i.e., less than 3 mph). • The three treatment types appear to be most effective at reducing speeds at Location C (intersection perception/response speed location), which is the point where the intersection would first become visible to the driver or where the driver might first react to the intersection. • Of the three treatment types tested, dynamic warning signs activated by speed may be the most effective at reducing speeds. However, this conclusion is based on only three intersection approaches. • Peripheral transverse pavement marking also appear potentially effective at reducing speeds. • Based on a limited number of sites, rumble strips do not appear to be as effective at reducing speeds as dynamic warning signs or transverse pavement markings. As described previously, the purpose of this research project was to identify and evaluate treatments and develop a set of guidelines that can be used by transportation professionals for reducing vehicle operating speeds on approaches to high-speed intersections. Therefore, in addition to the treatment testing, Phase II also included the development of NCHRP Report 3-74: Guidelines for Selecting Speed Reduction Treatments at High Speed Intersections (“Guidelines”). This document is intended to assist roadway planners, designers, and operators as they consider and select appropriate speed reduction treatments at intersections located in high-speed environments. While the application of these treatments most often applies to existing intersections that experience undesirably high speeds, the information is also relevant to new intersection designs. The Guidelines are not a new standard for implementing treatments. Rather, they are informational, describing good practices for selecting treatments. The Guidelines apply to intersections with approach speeds of 45 miles per hour (mph) or greater. Stop-controlled, yield-controlled, and uncontrolled approaches to signalized and unsignalized intersections are addressed. Because speeds tend to be lower in urban areas, the Guidelines primarily apply to suburban and rural roadways. Speeds on roadway segments outside the influence area of an intersection are not addressed; however, the relationship between segment speed and speed within the intersection influence area is addressed. This document focuses on public roadway intersections; however, many principles also apply to private driveways that include public-roadway–like features. The Guidelines include the following four sections and appendices: • Section 1 introduces the Guidelines and presents their purpose, scope and applicability. • Section 2 focuses on the role of speed in an intersection environment and discusses the ways in which speed affects intersection performance and the adjacent environment.

Chapter 1 NCHRP 3-74 Introduction Selection of Speed Reduction Treatments at High-Speed Intersections Page 1-6 • Section 3 guides users through the process of selecting speed reduction treatments for intersection approaches. The process includes: intersection pre-screening; treatment screening; and treatment implementation. • Section 4 describes speed reduction treatments in detail. This section contains an overview of each treatment, as well as more detailed descriptions, summaries of applicability and pertinent considerations such as maintenance, discussions of potential layouts and designs, and summaries of the documented effectiveness of each treatment in reducing speeds and improving safety. Photos and diagrams are also provided. The • The appendices to the Guidelines provide a diagnostic flow chart, scenario-based case studies, testing data and results from the testing plan, and references to other relevant studies. In addition to the research findings and Guidelines that resulted from this NCHRP project the research team found as many questions as it did answers throughout the course of this research effort. Therefore, given the limits and focus of this research project, during Phase II the team also identified other research topics for future consideration. 1.5 FINAL REPORT ORGANIZATION This Final Report is organized into seven chapters with supplemental information provided in the appendices: • Chapter 1 – Introduction • Chapter 2 – Preliminary Findings • Chapter 3 – Testing Plan • Chapter 4 – Treatment Installation • Chapter 5 – Testing Results • Chapter 6 – Guidelines • Chapter 7 – Future Research Suggestions • Appendix A – Literature Review Abstracts • Appendix B – Criteria for Prioritizing Sources • Appendix C – State Agency Survey • Appendix D – State Agency Survey Mailing List • Appendix E – Process for Selecting Recommended Treatments • Appendix F - Histograms of Speed Profile Data at 10 Sites • Appendix G - Speed Analysis by Individual Approach Location • Appendix H - Secondary Analysis of 85th-Percentile Speeds