National Academies Press: OpenBook

Safety Impacts of Intersection Sight Distance (2018)

Chapter: Front Matter

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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2018. Safety Impacts of Intersection Sight Distance. Washington, DC: The National Academies Press. doi: 10.17226/25082.
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Page ii
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2018. Safety Impacts of Intersection Sight Distance. Washington, DC: The National Academies Press. doi: 10.17226/25082.
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Page iii
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2018. Safety Impacts of Intersection Sight Distance. Washington, DC: The National Academies Press. doi: 10.17226/25082.
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Page iv
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2018. Safety Impacts of Intersection Sight Distance. Washington, DC: The National Academies Press. doi: 10.17226/25082.
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Page v
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2018. Safety Impacts of Intersection Sight Distance. Washington, DC: The National Academies Press. doi: 10.17226/25082.
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Page vi
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2018. Safety Impacts of Intersection Sight Distance. Washington, DC: The National Academies Press. doi: 10.17226/25082.
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Page vii
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2018. Safety Impacts of Intersection Sight Distance. Washington, DC: The National Academies Press. doi: 10.17226/25082.
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Page viii
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2018. Safety Impacts of Intersection Sight Distance. Washington, DC: The National Academies Press. doi: 10.17226/25082.
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Kimb Scott Kara Frank Richa VHB Ralei ACKNOWEDG This work was with the Feder which is admin Medicine. COPYRIGHT I Authors herein persons who o Cooperative R purposes. Per FMCSA, FRA, product, metho uses will give a request permis DISCLAIMER The opinions a are not necess or the program The informatio edited by TRB Safety erly Eccles Himes Peach Gross rd J. Porter gh, NC MENT sponsored by t al Highway Adm istered by the T NFORMATION are responsibl wn the copyrigh esearch Progra mission is give FTA, Office of d, or practice. ppropriate ack sion from CRP nd conclusions arily those of th sponsors. n contained in t . W Impac he American As inistration, and ransportation R e for the authen t to any previo ms (CRP) gran n with the unde the Assistant Se It is expected th nowledgment o . expressed or im e Transportatio his document w NC eb-Only ts of In sociation of St was conducted esearch Board ticity of their m usly published o ts permission to rstanding that n cretary for Res at those reprod f the source of a plied in this re n Research Bo as taken direct HR Docume tersecti ate Highway an in the Nationa (TRB) of the N aterials and for r copyrighted m reproduce ma one of the mate earch and Tec ucing the mate ny reprinted or port are those o ard; the Nation ly from the subm P nt 228: on Sigh Timothy Michigan East Lan Christop Portland Portland Contracto d Transportatio l Cooperative H ational Academ obtaining writte aterial used he terial in this pub rial will be used hnology, PHMS rial in this docu reproduced ma f the researche al Academies o ission of the a t Dista J. Gates State Unive sing, MI her M. Mons State Unive , OR r’s Final Repor n Officials (AAS ighway Resea ies of Science n permissions f rein. lication for clas to imply TRB, A, or TDC endo ment for educat terial. For oth rs who perform f Sciences, Eng uthor(s). This m nce rsity ere rsity t for NCHRP Pr Submitted Ja HTO), in coop rch Program (N s, Engineering, rom publishers sroom and not AASHTO, FAA rsement of a p ional and not-fo er uses of the m ed the researc ineering, and M aterial has not oject 17-59 nuary 2017 eration CHRP), and or -for-profit , FHWA, articular r-profit aterial, h. They edicine; been

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. C. D. Mote, Jr., is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.national-academies.org. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to increase the benefits that transportation contributes to society by providing leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Board’s varied committees, task forces, and panels annually engage about 7,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

iv CONTENTS LIST OF FIGURES ....................................................................................................................... vi  LIST OF TABLES ......................................................................................................................... vi  AUTHOR ACKNOWLEDGMENTS .......................................................................................... viii  ABSTRACT ................................................................................................................................... ix  SUMMARY .................................................................................................................................... 1  Chapter 1: Background ................................................................................................................... 4  Background on Study .................................................................................................................. 4  Study Objectives and Scope ........................................................................................................ 5  Approach to Achieve Objectives ................................................................................................ 6  Scope of this Document .............................................................................................................. 6  Chapter 2: Research Approach/Analytical Methodology ............................................................... 7  Overview ..................................................................................................................................... 7  Review of Existing ISD Practices and Relationships ................................................................. 7  Introduction ............................................................................................................................. 7  Literature Review.................................................................................................................... 7  Review of Documented Practices ......................................................................................... 13  Summary of Field Methods .................................................................................................. 24  Summary of Parameters ........................................................................................................ 24  Other Guidance ..................................................................................................................... 25  Review of Uncontrolled Intersection Sight Distance Methodologies ................................... 26  Field Data Collection ................................................................................................................ 32  Site Selection ........................................................................................................................ 32  Criteria for Inclusion ............................................................................................................. 32  Data Collection Methodology ............................................................................................... 35  Summary of Selected Sites ................................................................................................... 46  Analytical Method .................................................................................................................... 56  Chapter 3: Findings and Application ............................................................................................ 59  Overview ................................................................................................................................... 59 

v Final Models ............................................................................................................................. 59  Target Crashes ...................................................................................................................... 59  Target Fatal and Injury Crashes ............................................................................................ 62  Summary ................................................................................................................................... 65  Guidance Document Development .......................................................................................... 83  Vetting Process ..................................................................................................................... 83  Final Guidance Document .................................................................................................... 85  Chapter 4: Conclusions, Recommendations, and Suggested Research ........................................ 87  Conclusions and Recommendations ......................................................................................... 87  Incorporating Results into Practice ........................................................................................... 88  Dissemination ........................................................................................................................... 89  Suggested Future Research ....................................................................................................... 90  References ..................................................................................................................................... 91  Appendix A ................................................................................................................................. A-1 

vi LIST OF FIGURES Figure 1. Comparison of ISD Design Values for Uncontrolled Intersections. ............................. 30  Figure 2. Data Collection Site in North Carolina. ........................................................................ 34  Figure 3. Data Collection Sites in Ohio. ....................................................................................... 34  Figure 4. Data Collection Sites in Washington. ............................................................................ 35  Figure 5. Left- and Right-Directional Analysis Unit. ................................................................... 41  Figure 6. ISD Quality Condition 1. ............................................................................................... 43  Figure 7. ISD Quality Condition 2. ............................................................................................... 43  Figure 8. ISD Quality Condition 3. ............................................................................................... 44  Figure 9. Sighting Target .............................................................................................................. 45  Figure 10. Sample Chart. .............................................................................................................. 68  Figure 11. CMF for Target Crashes when Posted Speed Equals 35 mph. .................................... 69  Figure 12. CMF for Target Crashes when Posted Speed Equals 40 mph. .................................... 70  Figure 13. CMF for Target Crashes when Posted Speed Equals 45 mph. .................................... 71  Figure 14. CMF for Target Crashes when Posted Speed Equals 50 mph. .................................... 72  Figure 15. CMF for Target Crashes when Posted Speed Equals 55 mph. .................................... 73  Figure 16. CMF for Target Crashes when Posted Speed Equals 60 mph. .................................... 74  Figure 17. CMF for Target Fatal and Injury Crashes when Posted Speed Equals 35 mph. ......... 75  Figure 18. CMF for Target Fatal and Injury Crashes when Posted Speed Equals 40 mph. ......... 76  Figure 19. CMF for Target Fatal and Injury Crashes when Posted Speed Equals 45 mph. ......... 77  Figure 20. CMF for Target Fatal and Injury Crashes when Posted Speed Equals 50 mph. ......... 78  Figure 21. CMF for Target Fatal and Injury Crashes when Posted Speed Equals 55 mph. ......... 79  Figure 22. CMF for Target Fatal and Injury Crashes when Posted Speed Equals 60 mph. ......... 80  Figure 23. Example 1 – Target crashes. ........................................................................................ 81  LIST OF TABLES Table 1. Expected Crash Reduction Frequencies per Intersection per Year (David and Norman 1975). .............................................................................................................................................. 8  Table 2. Summary of Field Method. ............................................................................................. 16  Table 3. Summary of Parameters. ................................................................................................. 18 

vii Table 4. Summary of Other Policy Specifics. ............................................................................... 22  Table 5. Crash, Roadway, and Traffic/Operations Data Elements of Interest. ............................. 36  Table 6. Combination of Maneuvers. ........................................................................................... 40  Table 7. Crash Types Used in Identifying Angle Crashes. ........................................................... 40  Table 8. Sites Stratified by State, Area Type, and Terrain. .......................................................... 46  Table 9. Sites Stratified by State, Major Route Type, and Area Type. ........................................ 46  Table 10. Target Stratified by State and Year. .............................................................................. 47  Table 11. Summary Statistics for NC Continuous Independent Variables. .................................. 48  Table 12. Summary Statistics for NC Categorical Independent Variables. .................................. 49  Table 13. Summary Statistics for OH Continuous Independent Variables. ................................. 51  Table 14. Summary Statistics for OH Categorical Independent Variables. ................................. 52  Table 15. Summary Statistics for WA Continuous Independent Variables. ................................. 54  Table 16. Summary Statistics for WA Categorical Independent Variables. ................................. 55  Table 17. Model Estimation Results for Expected Number of Target Crashes. ........................... 61  Table 18. Model Estimation Results for Expected Number of Target Fatal and Injury Crashes. 63  Table 19. Descriptive Statistics for Variables in Target Crash Models. ....................................... 64  Table 20. Vetting Webinar Participants. ....................................................................................... 84 

viii AUTHOR ACKNOWLEDGMENTS The research reported here was performed under NCHRP Project 17-59 by VHB, Wayne State University, and Portland State University. VHB was the prime contractor for this study. Ms. Kimberly Eccles, P.E., Safety Practice Leader at VHB, was the Project Director and Principal Investigator. The other authors of this report are Dr. Scott Himes, P.E., Highway Safety Engineer at VHB; Ms. Kara Peach, Transportation Planner at VHB; Dr. Frank Gross, P.E., Highway Safety Engineer at VHB; Dr. Timothy Gates, P.E., PTOE, Associate Professor at Michigan State University (formerly of Wayne State University); and Dr. Christopher M. Monsere, P.E., Associate Professor at Portland State University. Dr. Richard Porter, P.E., Highway Safety Engineer at VHB, provided direction on specifying the statistical road safety models for crash modification factor development.

ix ABSTRACT This report documents the methodology and presents the results of a study aimed at estimating the safety effects of intersection sight distance (ISD) at stop-controlled intersections. To establish the relationship between ISD and safety at stop-controlled intersections, crash, traffic, and geometric data were collected for 832 intersection approaches with minor road stop control in North Carolina, Ohio, and Washington. These intersections represented a range of traffic volumes and major road cross section geometrics (e.g., two-lane, undivided; four-lane, undivided; four-lane, divided) in both urban and rural areas. Sites were selected for data collection without considering historic crash frequencies and severities. The data collection included field-measured ISD as a continuous variable using a standardized method as well as an exploratory measure of ISD quality. A cross-sectional study design with count regression modeling was used to quantify the relationship between safety and ISD. Target crashes were defined as those where a vehicle on the minor road collided with a vehicle on the major road. Target crash counts were associated with specific, measured values of an approach level ISD (i.e., one observation of target crash frequency in the database represents the target crash frequency for one minor road and major road approach combination). The results suggest that the expected numbers of target crashes and target fatal and injury crashes are associated with available ISD. Target crash frequencies increase as available ISD decreases. ISD quality may also impact safety performance, but it was not included in ISD crash modification functions (CMFunctions) that were created as part of this research. Results also suggest that ISD is associated with the expected number of target crashes in a non-linear fashion. The sensitivity of the expected number of target crashes to changes in ISD is highest when ISD is shorter, and decreases as ISD increases (i.e., the safety benefit of increasing ISD from 300 to 600 feet is substantially larger than the safety benefit of increasing ISD from 1,000 to 1,300 feet). Moreover, the results suggest that the impact of ISD on target crashes and target fatal and injury crashes varies as a function of the major road two-way annual average daily traffic (AADT) and the major road speed limit. The sensitivity of the expected number of target crashes to changes in ISD increases as both major road traffic volume and speed limit increase.

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TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 228: Safety Impacts of Intersection Sight Distance documents the methodology and presents the results from NCHRP Research Report 875: Guidance for Evaluating the Safety Impacts of Intersection Sight Distance. It provides the underlying research on estimating the safety effects of intersection sight distance (ISD) at stop-controlled intersections. To establish the relationship between ISD and safety at stop-controlled intersections, crash, traffic, and geometric data were collected for 832 intersection approaches with minor-road stop control in North Carolina, Ohio, and Washington.

NCHRP Research Report 875: Guidance for Evaluating the Safety Impacts of Intersection Sight Distance is a resource for practitioners involved in the planning, design, operations, and traffic safety management of stop-controlled intersections. It provides information on how to estimate the effect of ISD on crash frequency at intersections and describes data collection methods and analysis steps for making safety-informed decisions about ISD. The guidance also provides basic information on the importance of ISD that can be shared with decision makers and other stakeholders. A PowerPoint presentation that describes the project also accompanies the report and web-only document.

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