Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges (2021)

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363 APPENDIX A: PRACTITIONER INTERVIEWS This appendix describes the findings from interviews with practitioners on the topic of freeway and interchange safety. The findings were used to identify design and operational elements that have a significant effect on safety and knowledge gaps. This information was used to develop a methodological framework for a freeway and interchange safety prediction methodology and analysis tool. The framework is described in Chapter 3. OVERVIEW The primary objectives of the interviews were to: (1) obtain a sense of the type of issues encountered in the design and operation of freeways and interchanges and (2) identify the safety- related information needed by practitioners during the project planning and development processes. Three different groups were included in the interviews. One group included planners and engineers that were interviewed using a common set of questions. A second group included engineers at FHWA responsible for the review of interchange justification reports. A third group included engineers that have used ISAT to conduct an engineering analysis of interchange safety. The information obtained from each group is described in the next three subsections. The interviews revealed that a key motivation for the development of ISAT was the request for an interchange safety evaluation tool by several FHWA division offices. These offices (notably the Illinois office) indicated that tools were needed to support the safety evaluation for interchange and access justification reports. These reports are required for all proposed changes in access to the Interstate Highway System and must be approved by FHWA. INTERVIEWS WITH PLANNERS AND ENGINEERS A primary source of safety information was the interviews with engineering and planning professionals. Both in-person and telephone interviews were conducted. In-person interviews were held with state DOT engineers in Alabama, Illinois, Maryland, and Washington. Telephone interviews were conducted with 18 agencies representing FHWA field offices, state DOTs, and metropolitan planning organizations (MPO). The demographics of the agencies contacted for telephone interviews are listed in Table A-1. Collectively, 40 persons were interviewed in person and 22 persons were interviewed by telephone. The in-person interviews typically took place over several hours and included engineers involved in freeway concept planning, preliminary design, final design, traffic operation, and safety programs. The telephone interviews were intentionally kept to about 30 minutes and typically included only one or two individuals. To adhere to this time limit, only a subset of the questions used in the in-person interviews were used for the telephone interviews. In a few instances, the interviewees opted to conduct the interview by e-mail.

364 TABLE A-1. Demographics of telephone interview groups Expertise Agency Representation FHWA Field Offices State DOT MPO Engineering 4 8 1 Planning 1 1 3 Each interview typically consisted of three parts. The duration of each part was adjusted depending on whether the interview was in-person or via telephone. Initially, a presentation was made by the researchers to provide background information. An overview of the project was provided and ISAT was described. Then, the questions in Figure A-1 were posed in sequence and the responses recorded. Most of these questions were intentionally broad to encourage discussion and a free flow of ideas. A subset of the questions was used for the telephone interviews. The specific questions asked during each telephone interview were varied in a predetermined manner to ensure an equal number of responses were received for each question. Operational Issues 1. a. What are some common design problems or operational issues encountered in freeway projects? b. What are the safety concerns related to these problems or issues? 2. a. What are some common design problems or operational issues encountered in interchange projects? b. What are the safety concerns related to these problems or issues? 3. Are high-occupancy-vehicle (HOV) or high-occupancy-toll (HOT) lanes used? If yes, what are some common problems or issues encountered? Decision-Making Process 4. Is there some official guidance that... a. Describes how to evaluate safety? or, b. How to determine when there is a safety problem? 5. How does crash severity influence decisions? Level of Analysis Detail 6. For the planning stage of the project development process... a. Is it important to quantify the performance of the entire project? or b. Is it sufficient to evaluate a few select segments, ramps, or ramp terminals that are suspected of having issues? 7. For the design stage of the project development process... a. Is it important to quantify the performance of the entire project? or b. Is it sufficient to evaluate a few select segments, ramps, or ramp terminals that are suspected of having issues? Evaluation Tools or Techniques 8. What simulation models are used to evaluate traffic operation? 9. Were you aware of ISAT before today? a. If yes, are you having it used on your projects? b. What is the best thing about it? c. What could make it more useful? Figure A-1. Questions posed during the interviews.

365 A final element of the interview was an interactive session where specific design or operational elements were posed and the interviewees were asked to provide a number indicating the importance of each element. The responses to the questions in Figure A-1 are summarized in the following sections. Interview Questions Operational Issues The most commonly mentioned operational issue was freeway congestion. Its impact on crash frequency, manner of collision, and crash severity are issues for many of the interviewees. The long-standing belief that capacity improvements lead to safety improvements was cited by some. However, a more quantitative understanding of this relationship appears to be desired. Another issue that was frequently cited was bringing an alignment into compliance with the latest design criteria through reconstruction. By implication, this process should improve safety; however, a few interviewees indicated a desire for information that can be used to quantify this improvement. Topics that were mentioned often enough to be noteworthy include weaving section design and periodic maintenance pull-outs on urban freeways. Both elements are believed to have an influence on safety, but the relationship is undocumented. About one-half of the interviewed agencies indicate that HOV lanes are used in their state. Most of these agencies also have some HOT mileage. A range of issues was cited but with little commonality among them. This trend appears to reflect the wide range of HOV lane designs that are being used in the various states. A couple of interviewees noted that the speed differential between the HOV and adjacent lanes was a safety issue, especially when trucks were allowed in the HOV lane. Another issue cited by more than one interviewee was the lack of a shoulder of sufficient width to protect a stalled vehicle or facilitate enforcement in many barrier-separated HOV lanes. Decision-Making Process This question was answered by the state DOT interviewees. The tools for safety evaluation and safety problem identification vary among the states. Some use a site’s crash rate for evaluation and compare it to statewide averages for similar facilities to determine problem locations. Other states use an index value for safety evaluation, where the index represents a mathematical combination of crash frequency, severity, and rate. A couple of states noted that they were using (or planning to use) safety performance functions instead of statewide crash rates or indices as a basis for identifying problem locations. The severity of crashes is recognized as an important factor in evaluating the safety of a project or highway facility. Examples illustrating the consideration of severity typically focused on fatal crashes, or fatal crash rates. A couple of states indicated the use of a weighting system to compute a site’s severity index, where the weight given to each of the severity classes (K, A, B, C, PDO) decreases in an exponential manner, with fatality (K) weighted highest and property-damage- only (PDO) given negligible or no weight.

366 Level of Analysis Detail The planners and the engineers involved in concept planning described a need to evaluate the entirety of the project, regardless of whether the focus is cost, operations, or safety. Some interviewees indicated that the evaluation should reflect performance of the project over its design life. A similar sentiment was expressed by some engineers involved in preliminary design and final design; however, other engineers tended to have interest only in evaluating specific intersections, segments, or ramps. Evaluation Tools or Techniques Three simulation models were identified as being used to evaluate freeway segments or interchanges; they include: CORSIM, VISSIM, and SimTraffic. No one of these tools was mentioned notably more often than the other. Fourteen of the 18 telephone interviewees were not aware of ISAT prior to the interview. Similarly, three of the four state DOTs participating in the in-person interviews were not aware of ISAT. Of those that were aware of ISAT, only one interviewee was aware of it having been used for an engineering project. Given the limited prior awareness of ISAT, comments about its strengths and weaknesses were limited primarily to the participants of the in-person interviews (who had the benefit of a 30-minute ISAT presentation and demonstration). In this regard, it was offered that ISAT looked easy to use. There was some concern about the need for local calibration of the many safety performance functions in ISAT. Also, its ability to model only four ramp configurations (i.e., diamond, parclo, free-flow loop, and directional) was seen as a limitation. A lack of sensitivity to many geometric and operational design elements on the freeway, crossroad, and ramp (e.g., curve radius, weave section) was also seen as a limitation. Interactive Session Results During the interactive session, specific freeway and interchange elements were posed and the interviewees were asked to provide a number indicating the importance of each element. Specifically, they were asked to indicate: (1) the frequency with which an element was discussed during the planning or project development processes and (2) the perceived influence of the element on safety. The response to each question was one of three numbers based on the following scale: 0 - never/none; 1 - sometimes/some; 2 - often/high. Thus, two “scores” were recorded for each element, one score for frequency and one score for influence. The results of this session are shown in Tables A-2, A-3, and A-4 for freeway segments, interchange ramps, and interchange ramp terminals, respectively. The last column of each table indicates how the element ranked, relative to the other elements in the same table. The ranking is based on the product of the two scores. An element that ranks with a “1” is considered most frequently and is believed to have the most influence on safety, relative to the other elements listed.

367 TABLE A-2. Safety information needs for freeway segments Category Element 1 Rank 2 Roadway Lane width 12 Inside or outside shoulder width 2 Median width 9 Roadside and Safety devices in median Clear recovery distance 13 Side slope 4 Barrier length along embankments 3 Barrier type (say, to less rigid) 10 Median barrier 7 Crash cushions at roadside features 5 Alignment Horizontal curve radius 6 Superelevation of horizontal curve 8 Vertical grade 15 Other elements Continuous shoulder rumble strips 11 Highway illumination between interchanges 14 Distance between two ramps (e.g., weaving section) 1 HOVlane(s) 16 Use buffer-separation or barrier-separation for HOV lane 18 HOV lane entrance or exit frequency or location 17 Any Other: Interchange spacing Crest vertical curvature Lane drop (lane drop in curve) Lane add Congestion extent or duration Median crossover Truck-only facilities Lane balance at ramp ent. and exit Lane continuity along segment Signing consistency Ramp meter operation Barrier on curve (block sight lines) Tangent length between curves Shoulder use by bicyclists Notes: 1- Top ranking elements are identified by bold font. 2- 1 = most frequently considered and believed to have most influence on safety.

368 TABLE A-3. Safety information needs for interchange ramps Category Element 1 Rank 2 Roadway Ramp configuration (diamond, loop; direct, semidirect) 2 Lane width 13 Inside or outside shoulder width 12 Number of lanes 9 Roadside Clear recovery distance 10 Side slopes 8 Crash cushions at roadside features 1 Alignment Horizontal curve radius 3 Superelevation of horizontal curve 5 Vertical grade 4 Other elements Ramp illumination 10 Use of collector-distributor road 6 Weaving length on collector-distributor road 7 Ramp meter 14 Any Other: HOV bypass lane on entrance ramps Notes: 1- Top ranking elements are identified by bold font. 2- 1 = most frequently considered and believed to have most influence on safety. The number of responses that underlie a rank ranges from seven to ten, with nine being the most common. There was some variability in the responses for each element that reflects differences in opinion among the interviewees. Nevertheless, those elements in the top one-third of the rankings are consistently in the “more important” category for almost all interviewees. These elements have been identified in the table by bold font. Similarly, those elements in the bottom one-third of the rankings are consistently in the “less important” category for almost all interviewees. The last row in each of the three tables lists other elements that were identified during the interviews. In each instance, one or more interviewees felt that safety information about the element listed would be helpful in their work.

369 TABLE A-4. Safety information needs for interchange ramp terminal Category Element 1 Rank 2 Freeway speed-change lane Left-hand or right-hand ramp 11 Lane length (sensitivity to truck percent, grade, no. of ramp lanes) 2 Ramp illumination 12 Crossroad speed-change lane Provide (or not) 16 Crossroad ramp terminal Interchange type (SPUI, diamond, parclo) 1 Intersection skew angle 8 Left-turn lane or bay 5 Right-turn lane or bay 10 Left-turn lane length 6 Right-turn lane length 9 Outside shoulder width 15 Intersection median width 12 Sight distance restrictions 4 Driveway presence on crossroad approaches to intersection 3 Lane width 17 Channelized (free) right-turn lane 14 Illumination at terminal 7 Any Other: Ramp entrance or exit on freeway curve Design or signing treatments to reduce wrong-way maneuvers Roundabout crossroad ramp terminal Taper versus parallel entrance ramp Various (unnamed) pedestrian accommodations at terminals Ramp storage size to minimize queue spillback onto freeway Grade of terminal approach Notes: 1- Top ranking elements are identified by bold font. 2- 1 = most frequently considered and believed to have most influence on safety. MEETING WITH FHWA ENGINEERS The researchers met with engineers in FHWA’s Office of Infrastructure. This office has the responsibility of approving interchange justification reports and access justification reports. These reports have been required by FHWA since about the mid-1980s. In the early 1990s, FHWA’s policy for modifications to access to the Interstate Highway System was updated to require adherence to eight specific elements. The third element states that the proposed access point should “...not have a significant adverse impact on the safety and operation of the Interstate facility based on an analysis of current and future traffic.” This element provides the motivation for documenting the findings from a formal safety evaluation in the preparation of these reports.

370 Experience in reviewing justification reports indicates that the safety impacts of a proposed access point are often addressed through an assessment of its compliance with approved design criteria. In many instances, capacity improvements made in conjunction with the new access are cited as having an indirect safety benefit through the alleviation of queue spillback or bottleneck. It was noted that some interchange or access justification reports are prepared at a time in the project development process where some design details have not been determined. This situation can limit the level of analysis detail. Specific evaluation tools (e.g., ISAT or CORSIM) are not required for the safety or operations evaluation. The operations evaluation is only required when the freeway facility will experience congested flow conditions. The FHWA engineers estimated that these conditions are encountered in about one-half of the reports that they review. VISSIM is the most commonly used simulation tool used for operational evaluation. However, CORSIM is also often used and the Highway Capacity Manual methods are used in some situations. There are three ingredients that FHWA desires in the safety evaluation for an interchange or access justification report. First, the evaluation should address the entire project, as opposed to just selected locations or components. Second, the evaluation should reflect consideration of the crash history in the most recent three-year period for which crash data are available. These data would be used to identify locations in the project area at which crashes are relatively frequent. Third, the report should describe the proposed changes such that the project will not have a significant adverse effect on safety. The presence of HOV lanes on the freeway in the project vicinity is rarely a point of concern in the interchange or access justification report. Issues that have come up when reviewing these reports include: (1) the distance between the HOV entrance (or exit) and the nearest ramp terminal and (2) the speed differential between the HOV lane and adjacent through lane during peak traffic periods. The FHWA engineers have not found many reports where ISAT has been used in the safety evaluation. They believe that this trend may be a result of its limited ability to model complicated ramps and interchanges. They suggested that its capability should be broadened so that it could be used to evaluate ramp-to-ramp junctions, combined system and service interchanges, and complicated ramp alignments (e.g., braided ramps). INTERVIEWS WITH ISAT USERS The purpose of the interviews with ISAT users was to determine the types of applications for which ISAT is being used and to identify any useful improvements that could be made to it. Eleven professionals were identified as potential ISAT users. They were identified in a variety of ways, including information provided by FHWA’s Office of Safety R&D and leads provided during the interviews with planners and engineers. Each potential user was contacted by e-mail and asked to provide some feedback on their ISAT experience. Only three persons indicated that they had experience using ISAT (a few did not reply and a few others indicated that they had ISAT but have not had an occasion to use it).

371 One of the respondents used ISAT in preparation of an interchange justification report. The other respondents used it for environmental evaluations and planning studies. The stated benefits of using ISAT were: ● it can be used to evaluate a range of alternative interchange types, and ● it can predict crash frequency by severity. Identified areas of potential technical improvement for ISAT include the ability to evaluate the following design elements and components: ● weaving section design, ● left-hand versus right-hand ramps, ● the length of the marked gore area, ● auxiliary lane addition, and ● sensitivity to level of service or volume-to-capacity ratio. Identified areas of potential user-interface improvement for ISAT include: ● improved guidelines for model calibration, and ● ability to generate a user-friendly report of computed safety measures.