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30 CHAPTER 4 Development of New AMFs through Expert Panels This chapter includes a discussion of the second method- medium-high level of predictive certainty. Given this orienta- ology used in this study to develop AMFs--analysis-driven tion, expert panel membership needed to include expert expert panels. The chapter includes a listing of the partici- researchers knowledgeable about the AMFs of interest and the pants in each of the two panels convened, a description of the strengths and weaknesses of study methods and a group of overall process followed for the two panels with respect to expert state and local AMF users (i.e., safety engineers) with identifying and prioritizing the treatments to be explored, knowledge of both the specifics of the AMFs needed and of the and the results of the panel discussions. real-world conditions under which evaluated treatments were probably implemented. The decisions on expert panel mem- bership were made jointly by the Principal Investigators of the Introduction three involved NCHRP projects (NCHRP Projects 17-25, As noted in Chapter 2, one approach to AMF devel- 17-26, and 17-29). Members of the expert panels for each proj- opment/modification involved two analysis-driven expert ect are shown in Figure 1. panels. While other alternative expert panels were discussed during the project planning effort, it was decided by the team Procedures Followed and the oversight panel that a more critical need was to assist the research teams from NCHRP Projects 17-26 and 17-29 in The same procedures were followed for both expert pan- developing AMFs needed for the safety prediction tools they els. Both expert panels met for a 3-day period. Because the were developing for urban/suburban arterials and rural mul- number of potential AMFs was greater than could be stud- tilane highways. Because of the large number of serious and ied and discussed in this time frame, the AMFs were priori- fatal crashes that occur on two-lane rural roads, much of the tized before each meeting. For each meeting, The NCHRP past AMF development work has focused on treatments for Project 17-25 research team and the Principal Investigator that roadway class. Literature on AMFs for other roadway for each companion NCHRP project (17-26 and 17-29) de- classes is limited. It was hoped that expert panels might be veloped two lists of candidate treatments to consider for able to combine the limited past evaluations specific to these AMF development--one for roadway segments and one for two roadway classes (urban/suburban arterials and rural intersections. These lists were based on the results of the ear- multilane highways) with modified versions of rural two-lane lier-described AMF knowledge matrix and on the specific AMFs to develop the needed estimates. It was also hoped that AMF needs of the companion NCHRP projects. The two lists this option might produce multiple AMFs at a lower cost than were sent to each member of the expert panel before the the cost of new analyses. meeting. The expert panel members reviewed each list sepa- rately (intersection and segment treatments) and ranked each variable with respect to level of importance as either Members of the Panels primary (P) or secondary (S). Primary variables were those A critical requirement was that the expert panels be analysis- believed to be the most important predictors of safety on the driven. The AMFs derived by the panels were to be based on road type in question and in definite need of discussion at critical reviews of the existing research literature and on a con- the meeting. Secondary variables were those believed to be of sensus decision that the results from the research literature were less importance with respect to predicting safety, which robust enough to allow development of an AMF with at least a should only be considered for discussion at the meeting if
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31 Suburban and Urban Arterials Doug Harwood, Midwest Research Institute (Principal Investigator, NCHRP 17-26) David Harkey, UNC Highway Safety Research Center (Principal Investigator, NCHRP 17-25) Dr. James A. Bonneson, Texas Transportation Institute Dr. Forrest Council, VHB Kim Eccles, VHB Dr. Ezra Hauer, University of Toronto (Retired) Dr. Bhagwant Persaud, Ryerson University Stan Polanis, City Traffic Engineer, City of Winston Salem, NC Dr. Raghavan Srinivasan, UNC Highway Safety Research Center Tom Welch, State Transportation Safety Engineer, Iowa DOT Rural Multilane Arterials Dr. Dominique Lord, Texas A&M University (Principal Investigator, NCHRP 17-29) David Harkey, UNC Highway Safety Research Center (Principal Investigator, NCHRP 17-25) Dr. James A. Bonneson, Texas Transportation Institute Dr. Forrest Council, VHB Kim Eccles, VHB Dr. Ezra Hauer, University of Toronto (Retired) Loren Hill, State Highway Safety Engineer, Minnesota DOT Brian Mayhew, North Carolina DOT Dr. Bhagwant Persaud, Ryerson University (representing NCHRP 17-29) Dr. Raghavan Srinivasan, UNC Highway Safety Research Center Dr. Simon Washington, Arizona State University Tom Welch, State Transportation Safety Engineer, Iowa DOT UNC = University of North Carolina. VHB = Vanasse Hangen Brustlin, Inc. Figure 1. Members of the analysis-driven expert panels. time permitted. The primary variables were also ranked from the recommendation of an AMF or a listing of possible most important (first) to least important (last). These rank- resources that could be reviewed for future AMF develop- ings were based on each member's assessment of (1) the per- ment consideration. ceived magnitude of the effect of the variable on safety and · Copies of five cross-sectional studies. These studies in- (2) the quality and extent of reliable information in the lit- cluded a number of the high-priority elements. A descrip- erature on which an AMF could be based. The expert panel tion of the models developed and the variables included inputs were then compiled by the NCHRP Project 17-25 were provided for each study. The models could possibly team to develop a final list for discussion. provide additional insight into the direction and magni- The research team then developed and distributed to each tude of the effect of the variables found to be significant. expert panel member a resource notebook. This notebook · A draft procedure for adjusting AMF estimates and stan- included the results of the prioritization task, contact infor- dard errors. This procedure was developed and applied mation for all expert panel members, resource materials for under NCHRP Project 17-27. each variable/treatment, and pre-meeting assignments for the expert panel members. The resource materials included In order to ensure that all treatments or variables were ad- the following for each AMF under consideration: equately addressed, the expert panel members were given pre-meeting assignments. The expert panel was divided into · The AMF summary material developed in NCHRP Proj- three groups, and each group was assigned a subset of the ect 17-25 and described in Chapter 2 of this report. This variables to review prior to the meeting and asked to help lead material included the draft research results digest for those the discussion on those topics. The expert panel was asked to AMFs considered to have high or medium-high levels of focus on three questions: predictive certainty and summary pages from the interim report for those of lower quality. (1) Do the materials presented include enough quantitative · The AMF summary from NCHRP Project 17-27 (Parts I information to potentially develop an AMF for urban and II of the Highway Safety Manual). This draft summary and suburban arterials (or rural multilane highways)? was completed in 2005 and included assessments of AMFs; The materials provided to the panel included a wide spec- a discussion of the studies from which the AMFs were taken trum of study types (e.g., rigorous before-after studies, or derived; and a discussion of materials reviewed without simple before-after studies, cross-sectional studies, or less
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32 Table 17. Treatments reviewed and AMFs developed by expert panels. AMF Treatment Review PanelA CommentsC DevelopedB Intersection Treatments Intersection Skew Angle U/S Arterials No U/S Arterials Yes Left-Turn Lanes RML Highways No U/S Arterials Yes Right-Turn Lanes RML Highways No Intersection Medians U/S Arterials No Developed by separate 17-25 Signal Installation RML Highways No analysis U/S Arterials Yes Combined findings from two Left-Turn Phasing studies; further developed by RML Highways No separate 17-25 analysis Signal Change Interval U/S Arterials No Signal All-Red Interval U/S Arterials No Signal Cycle Length U/S Arterials No Right-Turn-On-Red (effects on Further developed by additional U/S Arterials Yes vehicle crashes) 17-26 analysis Right-Turn-On-Red (effects on U/S Arterials No Possible development in 17-26 pedestrian crashes) Driveways Near Intersection U/S Arterials No Intersection Sight Distance U/S Arterials No Curb Parking Near Intersection U/S Arterials No U/S Arterials Yes Further developed by additional Intersection Lighting RML Highways Yes 17-25 and 17-26 analysis Red-Light Cameras U/S Arterials Not needed Available from prior study (26) U/S Arterials Not needed Left-Turn Channelization RML Highways No U/S Arterials No Right-Turn Channelization RML Highways No Approach Speeds U/S Arterials No Roundabouts U/S Arterials Not needed Available from prior study (8) Roadway Segment Treatments Number of Lanes U/S Arterials No Lane Width U/S Arterials No U/S Arterials No Shoulder Type RML Highways Yes U/S Arterials No Shoulder Width RML Highways No Add a Median U/S Arterials No U/S Arterials No Developed by separate 17-25 Median Width RML Highways No analysis Two-Way Left-Turn Lane (TWLTL) U/S Arterials Yes Horizontal Curvature U/S Arterials No Possible development in 17-29 RML Highways No Sideslope RML Highways Yes Clearzone Width RML Highways No U/S Arterials No Developed by additional 17-26 Roadside Fixed Objects RML Highways No analysis U/S Arterials No 17-26 analysis produced separate Driveways/Access Points RML Highways No models for driveway accidents U/S Arterials No Developed by separate 17-25 Speed Limits/Zoning RML Highways No analysis On-Street Parking U/S Arterials Yes Further developed by additional Segment Lighting U/S Arterials Yes 17-25 and 17-26 analysis U/S Arterials Not Needed Rumble Strips RML Highways No Miscellaneous Treatments Pedestrian/Bicycle Treatments U/S Arterials No Some being developed in 17-26 Far-Side vs. Near-Side Bus Stops U/S Arterials No A Indicates which panel considered the treatment to be a priority, reviewed the relevant research, and discussed the potential for AMF development; U/S Arterials = urban/suburban arterials and RML Highways = rural multilane highways. B "Yes" indicates that consensus was reached at the expert panel meeting on an acceptable AMF from the critical review and discussion of prior research. C Numbers in "Comments" refer to NCHRP projects. Note that the 17-26 and 17-29 teams were involved in their respective panels.