Intersection Safety
Intersection Safety A Manual for Local Rural Road Owners http://safety.fhwa.dot.gov FHWA-SA-11-08
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Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. FHWA-SA-11-08 4. Title and Subtitle 5. Report Date Intersection Safety: A Manual for Local Rural Road Owners January, 2011 6. Performing Organization Code 8. Performing Organization Report No. 7. Author(s) Golembiewski, G.A. and Chandler, B. 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Science Applications International Corporation (SAIC) Mail Stop E-12-3 8301 Greensboro Drive McLean, VA 22102-3600 11. Contract or Grant No. DFTH61-05-D-00025, T-09-003 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Office of Safety Federal Highway Administration 1200 New Jersey Ave, SE Washington, DC 20590-9898 14. Sponsoring Agency Code HSSP 15. Supplementary Notes The Task Manager for this document was Rosemarie Anderson, FHWA Office of Safety. The Technical Oversight Working Group included John Dewar, Ed Rice, Joe Bared, and Fred Ranck, FHWA; Betsey Tramonte, FHWA Louisiana Division; David Anderson, Delaware Valley Regional Planning Commission; Bruce Drewes, Idaho Technology Transfer Center; Joe Fiocco, McMahon Associates, Inc.; Wayne Schoonover, Ionia County, Michigan Road Commission; and Bob Sperry, Iowa LTAP/CTRE. 16. Abstract According to the Federal Highway Administration, over 6 million lane-miles of roadway are in rural areas, and more than two-thirds of these rural roads are owned and operated by local entities. In 2008 56 percent of the 37,261 fatalities on U.S. roadways occurred in rural areas. Rural areas face a number of highway safety challenges due to the nature of their facilities. More than 20 percent of all traffic fatalities in the United States occur at intersections and over 80 percent of intersection-related fatalities in rural areas occur at unsignalized intersections. This document provides information on effectively identifying intersection safety issues in local areas, choosing the countermeasures that address them, and evaluating the benefits of those treatments. It is geared toward local road managers and other practitioners with responsibility for operating and maintaining their roads. It offers information on the procedures and processes to improve the safety of local rural unsignalized intersections and to reduce the potential for future crashes. 18. Distribution Statement 17. Key Words Intersection Safety, Intersections, Local, Rural, Unsignalized Intersections, Data, Field Review, Signs, Pavement Markings, Practitioner, Crashes, Implementation. 19. Security Clasif. (of this report) Unclassified No restrictions. 20. Security Clasif. (of this page) Unclassified Form DOT F 1700.7 (8-72) 21. No. of Pages 60 21. Price N/A Reproduction of completed page authorized
Table of Contents Table of Contents. i 1 Introduction and Purpose.1 1.1. The Intersection Crash Problem.1 1.2. State Intersection Safety Implementation Plans.3 1.3. Implementation Approaches.3 1.3.1. Systematic Approach.3 1.3.2. Spot Location Approach.4 1.3.3. Comprehensive Approach.5 1.4. Information in this Document.6 2 Identifying Safety Issues.10 2.1. 2.2. 2.3. 2.4. 2.5. 2.6. 3 State and Local Crash Databases. 11 Law Enforcement Crash Reports and Citations. 11 Observational Information. 12 Public Notifications. 14 Roadway Data. 14 Exposure Data. 15 Safety Analysis.16 3.1. Crash Frequency. 16 3.2. Crash Rates. 16 3.3. Geometric Issues. 18 3.3.1. Sight Distance.18 3.3.2. Skewed Geometry.20 3.4. Field Reviews. 21 4 Countermeasures.23 4.1. Enhanced Sign and Pavement Marking Improvements. 23 4.2. Select Intersection Countermeasures. 25 4.3. Funding Intersection Safety Countermeasures. 43 5 Evaluation . .44 6 Summary . .46 Appendix A Resources and References.A-1 Appendix B MUTCD Compliance Issues at Rural, Two-Way Stop-Controlled Intersections. B-1 i Intersection Safety
List of Tables Table 1 Sample Spreadsheet to Monitor Crashes/Observations at Local Intersections .13 Table 2 Example of the Intersection Crash Rate Calculation.17 Table 3 Design Intersection Sight Distance – Left Turn, Right Turn, and Crossing from a Stop.20 Table 4 Example Spreadsheet to Monitor Countermeasure Application History and Crash/Observational Data.45 List of Figures Figure 1 Intersection Fatalities by Year. 7-8 Figure 2 Steps to Address Intersection Safety.9 Figure 3 Sight Distance Triangles for 4-Leg Stop-controlled Intersections.19 Figure 4 Skewed Intersection.20 Figure 5 Basic Package for Intersections Experiencing Crashes.24 Intersection Safety ii
1 Introduction and Purpose Three million miles of local roads are maintained and operated by local administrators, township managers, and public works officials in more than 38,000 counties, cities, villages, towns, and tribal governments across the United States.1 One issue common to all local agencies is traffic safety. One of the most pressing traffic safety issues on local roads is intersection safety. Intersections can vary widely in terms of size, shape, number of entering legs, and number of turn lanes. According to the American Association of State Highway and Transportation Officials’ (AASHTO) A Policy on Geometric Design of Highways and Streets, an intersection is defined as the general area where two or more highways join or cross, including the roadway and roadside facilities for traffic movements within the area. Each highway radiating from an intersection and forming part of it is an intersection leg. The most common intersection where two highways cross has four legs. Intersections generally involve through- or cross-traffic movements and typically involve turning movements between the highways. There are three general types of highway crossings – at-grade intersections, grade separations without ramps, and interchanges. This document addresses safety issues related to at-grade intersections. Local rural roads also encompass a wide range of surface types, including paved facilities, gravel roads, and dirt roads. Many local rural intersections lack suitable design standards, delineation, and signing that may be provided on higher volume roadways. Further, many were not officially designed, but rather “evolved” over time to their current geometric configuration. 1.1. The Intersection Crash Problem In 2008 the National Highway Traffic Safety Administration (NHTSA) indicated that 56 percent of the 37,261 fatalities on U.S. roadways occurred in rural areas.2 This figure is disproportionate since only 23 percent of Americans live in rural areas3 and rural roadways account for just 40 percent all vehicle miles traveled nationally.4 1 2 3 4 1 McNinch, T.L. and Colling, T.K. “Traffic Safety Education for Nonengineers.” Public Roads, May/June, 2009, pp. 32-39. Available at: 9june/05.cfm National Highway Traffic Safety Administration, Traffic Safety Facts: 2008 Data (Washington, DC: 2009). Available at: http://www-nrd.nhtsa.dot.gov/Pubs/811164.pdf U.S. Department of Transportation, “Rural Safety Initiative,” web page, February 2008. Available at: initiativeplan.htm U.C. Berkeley, Safe Transportation Research & Education Center, “Rural Road Safety” web page. Available at: ml Intersection Safety
More than 20 percent of all traffic fatalities in the United States occur at intersections, both signalized and unsignalized. As shown in Figure 1, the number of intersection-related fatalities has been decreasing since 2005, yet the overall number is still very high. More than 80 percent of rural intersection fatalities occur at unsignalized intersections. Due to this high proportion of crashes at these types of intersections, unsignalized intersections will be the focus of this report. For information on safety at signalized intersections, please refer to Signalized Intersections: Informational Guide5 and NCHRP Report 500, Volume 12, A Guide for Reducing Collisions at Signalized Intersections.6 9500 9362 9300 9273 9100 8922 8900 8700 9238 9176 8850 8703 8689 8500 8300 8100 7900 7809 7700 7500 2000 2001 2002 2003 2004 2005 2006 2007 2008 Figure 1 – Intersection Fatalities by Year According to FHWA, the most severe crash type at unsignalized intersections is a right-angle crash. This crash type typically occurs when two vehicles approaching at a perpendicular angle collide due to one vehicle failing to stop or yield right of way from a Stop or Yield sign. In recent data analyses commissioned by the Federal Highway Administration (FHWA), every 100 reported angle crashes at unsignalized intersections resulted in approximately 1 to 3 fatalities and 5 to 15 serious injuries.7 5 6 7 U.C. Berkeley, Safe Transportation Research & Education Center, “Rural Road Safety” web page. Available at: ml Antonucci, N. et al., A Guide for Reducing Collisions at Signalized Intersections, TRB, National Research Council, NCHRP Report 500, Vol. 12, 2004. Available at: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp rpt 500v12.pdf Federal Highway Administration, “State Intersection Safety Implementation Plans,” 2008-2010. (unpublished studies) Intersection Safety 2
1.2. State Intersection Safety Implementation Plans FHWA recognized that while a number of States had intersection safety as an emphasis area in their Strategic Highway Safety Plans (SHSP), they lacked an action plan to guide their intersection safety implementation activities on State and local roads. To date, FHWA has worked with 11 States to develop Intersection Safety Implementation Plans (Arizona, Florida, Georgia, Indiana, Louisiana, Mississippi, Missouri, Ohio, Pennsylvania, South Carolina, and Tennessee).8 The plans include the activities, countermeasures, strategies, deployment levels, implementation steps, and estimate of funds necessary to achieve the intersection component of the State’s SHSP goal. Local road practitioners should consult their State’s Intersection Safety Implementation Plan, if available, before embarking on an improvement strategy. 1.3. Implementation Approaches Local practitioners should consider implementation methodology when seeking to address intersection safety within their jurisdiction. Typical approaches include: Systematic approach; Spot location approach; and Comprehensive approach incorporating human behavior issues. 1.3.1. Systematic Approach For the systematic approach, the analysis is based on crash types and proven safety countermeasures selected based on those types. In one application of the systematic approach, common crash types are selected from analysis. Locations experiencing these crash types and locations with similar geometric features as those experiencing selected crash types are selected and treated systematically with low-cost safety countermeasures. Another application of the systematic approach begins with identifying low-cost, effective countermeasures to common traffic safety issues. Once a basic set of countermeasures is identified, the crash data system is analyzed to choose locations where the countermeasures can be costeffectively deployed. Estimates of the impacts of implementation can be made in terms of deployment cost and the benefits measured in traffic crash reduction. 8 3 An example Intersection Safety Implementation Plan is available at: sfty imp pln0709/index.cfm#toc Intersection Safety
Benefits of the systematic approach may include: Widespread effect. The systematic approach can impact safety issues at a large number of locations on an entire local roadway network. Crash type prevention. Using predominant crash types with a high or moderate level of crashes, an agency can address locations that have not yet experienced these crash types, but have similar characteristics to locations with such crash histories (e.g., geometric conditions, traffic volume). Cost-effectiveness. Implementing low-cost solutions across an entire system can be a more cost-effective approach to addressing system-wide safety. Reduced data needs. The systematic approach can be used without detailed crash history for specific locations, reducing data needs. Drawbacks of the systematic approach may include: Justifying improvements can be difficult. Because this approach does not always address locations with a history of crashes with recommended treatments, it can be difficult to justify improvements at locations without crash history. The systematic approach will rarely include a recommendation for a large-scale safety improvement at a single location. Since these are the types of projects that garner attention from decision makers, the media, elected officials, and the general public, it can require additional effort from the safety practitioner to explain the systematic approach and its benefits to those groups. 1.3.2. Spot Location Approach The spot location approach has typically been based exclusively on an analysis of crash history. Due to the fact that some locations in a jurisdiction may have a significantly higher number of crashes than most of the others, it is important to identify those locations and treat them accordingly. The benefits to the spot location approach may include: Focus on demonstrated needs. The spot location approach focuses directly on locations with a history of crashes and addresses them. Drawbacks of the spot location approach may include: Assumption that the past equals the future. This approach assumes locations with a history of crashes will continue to have the same number and type of crashes in the future. Minimal overall benefit. This approach often focuses on specific locations, and because of this, it is difficult to have a significant impact on the entire network. Intersection Safety 4
The spot location approach to traffic safety can be implemented in parallel with the systematic approach to provide the best combination of safety treatments in a jurisdiction. In addition, the spot location approach could be applied to those locations that have had low-cost countermeasures installed systematically but, after an assessment, continue to show a higher than average crash rate. 1.3.3. Comprehensive Approach The comprehensive approach introduces the concept of the 4 E’s of Safety; Engineering, Enforcement, Education, and Emergency Medical Services. This approach recognizes that not all locations can be addressed solely by infrastructure improvements. Incorporating other elements is often required to achieve marked improvement in intersection safety. Some intersections will be identified that have frequent driving violations for which targeted enforcement is an appropriate countermeasure. In general, the most common violations at intersections are speeding, failure-to-yield, aggressive driving, failure to wear safety belts, and driving while impaired. When locations are identified that have reports and observations of these violations, coordination with the appropriate law enforcement agencies is needed to deploy visible targeted enforcement at the identified intersections to reduce the potential for future driving violations and related crashes. Education and outreach efforts should supplement enforcement to improve the effect of each. 5 Intersection Safety
1.4. Information in this Document The purpose of this document is to provide information on effectively identifying intersection safety issues and countermeasures that address them, leading to the effective implementation of safety projects. This includes pertinent information regarding the Manual on Uniform Traffic Control Devices (MUTCD) requirements, guidance on conducting field reviews, identification of unsignalized intersections with multiple crashes and/or high potential for future crashes, selection of the appropriate low-cost improvement at these intersections, and evaluation of safety projects and processes. This document is intended to provide appropriate intersection safety information in one report. Some practitioners responsible for the safety of the local road network may not have formal safety-specific highway training; this can present a challenge in reducing the risk of crashes at rural unsignalized intersections on local roads. In addition, the person responsible for highway safety may have multiple responsibilities including public works functions, such as water and/or wastewater treatment, trash collection, and snow removal. In these cases, roadway safety and infrastructure maintenance may be only a small part of the job. The report is not intended as a comprehensive guide for intersection design and improvement. It does, however, provide a framework that can be used to assess the safety of existing intersections and determine whether additional countermeasures should be installed. This document suggests a process for the planning and implementation of intersection safety improvements. The processes discussed in this document are summarized in Figure 2. Intersection Safety 6
Step 1 Identify Intersection Safety Issues (Manual: Section 2) Safety issues can be identified by collecting crash history, roadway, and exposure information from the following sources: State and local crash databases Law enforcement crash reports and citations Observations by law enforcement or road maintenance crews Public notifications Hospital records State and local roadway databases Traffic count records Step 2 Record Information for Safety Analysis (Manual: Table 1) Compile information in a table that includes the source of the information, the type of problem, and other attributes of the crash, observation, or notification. Steps 3 & 4 Data Analysis, Countermeasure Selection, and Installation Depending on the approach, the order of data analysis, countermeasure selection, and countermeasure installation steps may vary. Spot Location Approach and Systematic Approach (Crash Type Focus) 7 Intersection Safety Systematic Approach (Countermeasure Focus)
Spot Location Approach and Systematic Approach (Crash Type Focus) Systematic Approach (Countermeasure Focus) Step 3 Step 3 Analyze Data Select Countermeasures (Manual: Section 3) (Manual: Section 4) Data can be analyzed in the following ways, based on available information: Crash frequency Crash rate calculations Qualitative analysis Develop a list of countermeasures and thresholds for their application (e.g. crash frequency, crash type, traffic volumes). Step 4 Step 4 Select and Install Countermeasures (Manual: Section 4) Analyze Data and Install Countermeasures (Manual: Section 3 and 4) Details from crash data and analysis feeds the countermeasure selection process. Enhanced signing Transverse rumble strips Clear sight triangles Other Search crash data for the criteria identified in Step 3. Determine cost-effective level of deployment for each countermeasure. Step 5 Assessment and Follow-up (Manual: Section 5) Evaluate intersection safety treatments after installation. Track countermeasure installations Monitor crash experience at treated locations Figure 2 – Steps to Address Intersection Safety Intersection Safety 8
Section 2 of this manual provides an overview of the types of data to collect for the identification of intersection safety issues. It discusses the sources of crash data and how they can be used. Additionally, types of roadway data used in safety analyses are introduced. Section 3 summarizes the types of analysis that can feed the issue identification and countermeasures selection process. This discussion builds on the types of information and data discussed in Section 2 and provides definitions and examples of the factors that should be considered. Section 4 provides a description of selected countermeasures that have been shown to improve safety at unsignalized intersections on local rural roads. It includes a basic set of strategies – supplementary warning signs and pavement markings – to install at locations experiencing a history of crashes. The section also introduces additional safety strategies, including flashing beacons on Stop signs and turn lane modifications. The steps to complete an evaluation are presented in Section 5. After the countermeasures are installed, assessing their effectiveness will provide valuable information and can help determine which countermeasures should continue to be installed on other intersections to make them safer as well. In Section 6 a summary of the overall content of the manual is presented. A list of resources and references is presented in Appendix A. It includes publications that focus on intersection countermeasures, research that supports their use, and various studies that document their effectiveness. The appendix also includes references that focus on the use of datadriven processes for countermeasure selection, assessment procedures and strategies, descriptions of successful programs, and national programs that may help identify resources to support local efforts. Appendix B addresses compliance with MUTCD minimum requirements for rural unsignalized intersections. The MUTCD provides the standards used by road managers nationwide to install and maintain traffic control devices on all public streets, highways, bikeways, and private roads open to public traffic. 9 Intersection Safety
2 Identifying Safety Issues Determining what the problems are and where they are occurring will assist in making the most informed decisions regarding countermeasure selection and implementation to address intersection safety issues. When conducting a safety analysis, a minimum of 3 years of data is desired to obtain an accurate picture of the crash history within a jurisdiction, since crashes are relatively rare events and are not universally distributed across all intersections. A relatively large representative sample size for crashes in the jurisdiction will increase the chance that locations with the most severe safety issues will be identified. Due to the possibility of changes in traffic patterns and the roadway itself, data more than 5 years old are typically not desirable for assessing safety issues. Analysis can range from simple “push pin” maps for identifying crash clusters to statistical analyses of crash rates, depending on the crash history and other data available. There are a number of information sources used to identify crashes and risk factors at rural intersections. These include: State and local crash databases; Law enforcement crash reports and citations; Observational information from road maintenance crews and law enforcement; and Public notification of safety concerns. In order to determine the intersections with a history of crashes (and those with a potential for future crashes), it is important to consider the types of data available and how those data can be used. In addition to the location of the crashes, the data can also provide information regarding crash causation to help identify potentially effective countermeasures. The types of data available can range from anecdotal information, such as public input, to crash databases provided by State or local agencies. In some cases it may be beneficial to collect data from multiple sources to identify safety issues occurring at intersections. The following discussion presents the most common information sources and recommendations for their use. Intersection Safety 10
2.1. State and Local Crash Databases Each State has a central repository for storing crash data that identifies locations with crash occurrences. Information found in a typical crash database includes; time and date of the crash, location, crash type, crash severity, and weather conditions. These data can be used to help compare a jurisdiction’s intersections with others in the State. This comparison can help determine the level of need as it relates to similar locations in the region. Often States will provide or assist local agencies with their crash data analysis needs. Crash data is typically stored by the State Department of Transportation (DOT), Department of Public Safety (DPS), or Department of Revenue (DOR). In addition, some local jurisdictions keep their own crash and roadway databases. If these exist, the information can be used as described above. Action: Depending on your State’s organizational structure, contact the county, regional, or State engineer or your State’s Local Technical Assistance Program (LTAP) representative to determine if crash data within your jurisdiction is available for your use. If available, obtain 3 to 5 years of crash and roadway characteristic data. Develop a spreadsheet for intersections with a history of crashes (see Table 1). This can serve as a basic database to help identify common crash characteristics and identify appropriate countermeasures. 2.2. Law Enforcement Crash Reports and Citations If an agency does not have access to State crash databases, law enforcement crash reports can be a valuable tool to identify the location and contributing circumstances to intersection crashes. The following variables (at a minimum) should be extracted and compiled from the crash reports: 11 Location; Date and time; Crash type; Crash severity; Weather conditions; Sequence of events; and Contributing circumstances. Intersection Safety
Review of law enforcement crash reports can support decisions regarding the locations to improve and the safety treatments to select. While the information collected by law enforcement personnel may differ by jurisdiction, the basic elements should provide sufficient data to identify intersections that need improvement. Citation records by law enforcement can provide information regarding driver behavior issues within a jurisdiction. Though not correlated directly to crash locations, citation information can indicate overall issues in the region that can potentially be addressed with enforcement and education strategies. Police reports should be reviewed periodically in order to compile the necessary information for conducting an analysis. This information can also be stored in the spreadsheet shown in Table 1. Action: Develop a relationship with law enforcement officials responsible for enforcement and crash investigation on their roads. This could foster cooperation in sharing crash reports and safety information and collaboration on problem intersections. 2.3. Observational Information The crews who maintain t
Table 3 Design Intersection Sight Distance - Left Turn, Right Turn, . administrators, township managers, and public works officials in more than 38,000 counties, cities, villages, towns, and tribal governments . system can be a more cost-effective approach to addressing system-wide safety. Intersection Safety intersection safety .
Displaced Left-Turn Intersection (DLT) 31 . Source: Google Earth . DLT in West Valley City, UT . The left-turns are displaced in advance of the intersection through two-phase signals. This can be done as a partial or full D\ൌT intersection. Median U-Turn Intersection (MUT) 32 .
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3 convex-convex n [DK85] convex-convex (n;lognp lognq) [DK90] INTERSECTION DETECTION OF CONVEX POLYGONS Perhaps the most easily understood example of how the structure of geometric objects can be exploited to yield an e cient intersection test is that of detecting the intersection of two convex polygons. There are a number of solutions to this .
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Multiparty Cardinality Testing for Threshold Private Set Intersection Pedro Branco Nico D ottlingy Sihang Puz February 26, 2021 Abstract Threshold Private Set Intersection (PSI) allows multiple parties to compute the intersection of their input sets if and only if the intersection is larg
WSDOT Design Manual M 22-01.15 Page 1300-1 July 2018 Chapter 1300 Intersection Control Type 1300.01 General. 1300.02 Intersection Control Objectives. 1300.03 Common Types of Intersection Control. 1300.04 Modal Considerations. 1300.05 Procedures. 1300.06 Do
MEDIAN U-TURN INTERSECTION (MUT) - (Also Known as Median U-Turn Crossover, Boulevard Turnaround, Michigan Loon and ThrU-Turn Intersection).* Replaces all direct left turns at an intersection with indirect left turns using a U-turn movement in a wide median. Eliminates left turns on both intersecting side streets and the major street.
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