Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges (2021) / Chapter Skim
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From page 43... ...
4-1 The assessment of A.I.I. alternatives for pedestrians and bicyclists is an integral part of the Intersection Control Evaluation (ICE)
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4-2 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Exhibit 4-1. Overview of the assessment framework for pedestrian and bicyclist safety at A.I.I.s.
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Assessment 4-3 It is critical in the design process to decide on the pedestrian and bicycle facility type early; the decision can directly affect overall right-of-way needs and many subsequent design decisions. For pedestrians, sidewalks should be sized depending on local context and functional classification (see Chapter 2)
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From page 46... ...
4-4 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges PLOS categorizes quality of service for pedestrians on an A to F scale, where PLOS A is excellent or very comfortable for pedestrians, and F is very poor, indicating a very uncomfortable experience for pedestrians. Exhibit 4-3 tabulates the effect that various PLOS inputs have on the PLOS score for street segments and signalized intersections, where a higher score worsens the PLOS rating of the link or intersection.
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Assessment 4-5 A factor in calculating PLOS involves the delay experienced by pedestrians. When a delay is perceived as excessive, pedestrians are more likely to take risks in crossing a conflicting traffic stream.
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4-6 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Generally, the scoring accounts for the "friction" between users of different modes -- pedestrians, bicyclists, runners, in-line skaters, and child bicyclists -- as they pass one another using the trail. This friction is influenced by (1)
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Assessment 4-7 range in integer values from 1 to 4, with more stressful conditions on the higher end of the range (LTS 3 or LTS 4)
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4-8 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges 4.4 Design Flag Assessment As a surrogate for quantitative performance measures, performance measures -- also known as design flags -- can help identify potential safety, accessibility, operational, or comfort issues for pedestrians and bicyclists. A design flag does not necessarily represent a fatal flaw for an alternative; rather, it presents a design issue that should be addressed in the iterative development and evaluation of the alternative.
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Assessment 4-9 Sec. Design Flag Bikes Peds.
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4-10 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges For designs in which there is more than one way to complete a particular movement (e.g., a shared-use path adjacent to an on-street bicycle lane) , the analysis should select one of these options and remain consistent over the evaluation of all flags.
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Assessment 4-11 each flag. The following sections present each design flag in detail.
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4-12 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges This motor vehicle right-turn design flag can be categorized as either yellow or red, depending on two dimensions: (1) vehicle right-turn speed, and (2)
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From page 55... ...
Assessment 4-13 equal to 50 veh/h are therefore given a yellow flag, while a turning speed or volume beyond these thresholds increases the safety risk for the pedestrian and results in a red flag. Exhibit 4-11 shows a traditional four-legged intersection with both exclusive right-turn lanes and shared through-right lanes.
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4-14 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Exhibit 4-14. Design Flag 2 – Yellow- and red-flag thresholds.
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Assessment 4-15 applications, it is important to consider any shy distance requirements from the edge of the travel lanes, or vertical obstructions. In both cases, the "effective width" is reduced by 2 feet each, recognizing that bicyclists cannot ride immediately next to these obstructions.
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4-16 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges at channelized turn lanes and in some A.I.I. configurations, this may not always be the case.
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Assessment 4-17 4.4.4 Crossing Yield-Controlled or Uncontrolled Vehicle Paths The flag for crossing yield-controlled or uncontrolled vehicle paths is shown in Exhibit 4-19. Focus group discussions indicated yield-controlled and uncontrolled crossings of vehicle and pedestrian paths lead to uncomfortable and potentially unsafe interactions.
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4-18 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges speed-radius relationship found in the AASHTO Green Book or measured in the field, while vehicle volumes are available from traffic forecasts or local counts. This flag applies to both pedestrian and bicycle paths.
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From page 61... ...
Assessment 4-19 The level of comfort in this assessment category is not strictly a function of the number of crossings (e.g., provision of midblock refuge to create a two-stage crossing) , but rather from multiple crossings that do not lead directly to the desired destination.
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4-20 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Exhibit 4-24. Design Flag 5 example.
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Assessment 4-21 4.4.6 Executing Unusual Movements The executing unusual movements design flag is shown in Exhibit 4-26. Design consistency helps roadway users by setting expectations for how to move around a network and through an intersection.
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4-22 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges proceeds across the intersection into a two-way cycle track. In most locations, the presentation of an exclusive bicycle lane developing between two vehicular lanes and proceeding at an angle through an intersection would be considered an unusual movement.
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Assessment 4-23 refuges, for crossing one direction of travel at a time, and for having raised separation between opposing directions of traffic. Similar considerations apply for bicyclists.
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4-24 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges a particular origin-destination movement must be completed. These delays should be minimized to the extent possible.
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Assessment 4-25 A planning-level estimation of delay can be made using the equation below. This method assumes random arrival at the intersection.
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4-26 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges 4.4.9 Undefined Crossings at Intersections The undefined crossings at intersections design flag is shown in Exhibit 4-36. For all intersection forms, unmarked or undesignated space at an intersection can lower the level of comfort when walking or biking.
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Assessment 4-27 Exhibit 4-38. Design Flag 9 example.
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4-28 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges This design flag can be categorized as either yellow or red, depending on two dimensions: (1) vehicle turn speed, and (2)
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Assessment 4-29 left-turning movement and thus increase vehicle delay and the likelihood of a driver accepting an inappropriately small gap in the pedestrian flow. Exhibit 4-43 shows a more traditional permissive left-turn conflict with two-directional traffic.
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4-30 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Exhibit 4-44. Design Flag 11 – Intersecting driveways and side streets.
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Assessment 4-31 Exhibit 4-46. Design Flag 11 example.
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4-32 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges 4.4.12 Sight Distance for Gap Acceptance Movements The design flag describing sight distance for gap acceptance movements is shown in Exhibit 4-48. Throughout the design, sight distance must be provided.
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Assessment 4-33 Flag Applicable Mode Measure of Effectiveness Yellow-Flag Threshold Red-Flag Threshold Sight distance for gap acceptance movements Pedestrian & Bicycle Sight Distance N/A Less than required for vehicle speed Exhibit 4-49. Design Flag 12 – Red-flag thresholds.
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4-34 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges appropriate sight distance for pedestrians standing on the northeast quadrant preparing to cross the mainline to the west. 4.4.13 Grade Change The grade change design flag is shown in Exhibit 4-52.
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Assessment 4-35 4.4.14 Riding in Mixed Traffic The riding in mixed traffic design flag is illustrated in Exhibit 4-55. As noted in Chapter 3, riding in mixed traffic next to motorized vehicles with high speeds, high volumes, or both have been documented as both a safety issue and a comfort issue for bicyclists.
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4-36 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Exhibit 4-57 shows an intersection with a posted 25 mph speed limit on the east-west street and a 35 mph speed limit on the north-south street. On both streets, there is a dedicated bike lane with no buffer.
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Assessment 4-37 cross may occasionally lead to a bicyclist being in the intersection when a conflicting movement receives a green indication. • At many signals, a cyclist can only rely on the yellow indications for motorists.
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4-38 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges a bicycle, therefore, requires 3 to 5 times the clearance times calculated for motorized traffic. This flag can only be applied to bicycle movements.
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Assessment 4-39 Exhibit 4-62. Design Flag 16 – Yellow- and red-flag thresholds.
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4-40 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Exhibit 4-64. Design Flag 17 – Bicyclists traveling in channelized lane adjacent to motor vehicles.
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Assessment 4-41 speed might be higher or lower than the design speed given the intersection environment. The channelization length should be measured from the design concepts, aerial surveys, or field measurements.
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4-42 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Exhibit 4-67. Design Flag 18 – Turning motorists crossing bicycle path.
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Assessment 4-43 Exhibit 4-69. Design Flag 18 example.
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4-44 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Typically, the downstream situation is more severe because merging traffic has to switch lanes across the bike path (see flag #18) , but both situations can be of concern for cyclists.
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Assessment 4-45 Exhibit 4-74. Design Flag 19 example.
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4-46 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges 4.5 Design Flag Assessment Scoring Sheets Exhibit 4-78 and Exhibit 4-79 can be used as scoring sheets. A new sheet should be used for each design alternative.
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Assessment 4-47 Pedestrian Flags NCHRP 7-25 Method Date: Project: Alternative: Intersection/Interchange: Analyst: No. Name West East North South 1 Motor Vehicle Right-Turn 2 Uncomfortable/ Tight Walking Environment 3 Nonintuitive Motor Vehicle Movement 4 Crossing Yield or Uncontrolled Vehicle Paths 5 Indirect Paths 6 Executing Unusual Movements 7 Multilane Crossing 8 Long Red Times 9 Undefined Crossing at Intersections 10 Motor Vehicle Left-Turn 11 Intersecting Driveways and Side Streets 12 Sight Distance for Gap Acceptance 13 Grade Change Total Possible Flags Total Yellow Flags Total Red Flags PCT Yellow PCT Red PCT Flagged Indicate R=red flag, Y=yellow flag, or blank=no flag Study Area Sketch with Path Assignment Exhibit 4-78.
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4-48 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Bicycle Flags NCHRP 07-25 Method Date: Project: Alternative: Intersection/Interchange: Analyst: No. Name N BL N BT N BR SB L SB T SB R EB L EB T EB R W BL W BT W BR 4 Crossing Yield or Uncontrolled Vehicle Paths 5 Indirect Paths 6 Executing Unusual Movements 7 Multilane Crossing 8 Long Red Times 9 Undefined Crossing at Intersections 10 Motor Vehicle Left-Turn 11 Intersecting Driveways and Side Streets 12 Sight Distance for Gap Acceptance 13 Grade Change 14 Riding in Mixed Traffic 15 Bicycle Clearance Times 16 Lane Change Across Motor Vehicle Lanes 17 Channelized Lanes 18 Turning Motorists Crossing Bicycle Path 19 Riding Between Travel Lanes 20 Off-Tracking Trucks in Multilane Curves Total Possible Flags Total Yellow Flags Total Red Flags PCT Yellow PCT Red PCT Flagged Indicate R=red flag, Y=yellow flag, or blank=no flag Study Area Sketch with Route Assignment Exhibit 4-79.
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From page 91... ...
Assessment 4-49 4.6 References 1.
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