Posted Speed Limit Setting Procedure and Tool: User Guide (2021) / Chapter Skim
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11 Roadway Segment Context and Type The initial step in decision-making is identifying the roadway segment content and type. The Expanded Functional Classification System (Expanded FCS)
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12 Posted Speed Limit Setting Procedure and Tool: User Guide • Suburban: areas with medium density, mixed land uses within and among structures (including mixed-use town centers, commercial corridors, and residential areas) , and varied setbacks.
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Decision-Making Steps Within the Suggested Speed Limit Procedure 13 • Principal Arterials: corridors of regional importance connecting large centers of activity. • Minor Arterials: corridors of regional or local importance connecting centers of activity.
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14 Posted Speed Limit Setting Procedure and Tool: User Guide low/medium because of the competing issues within these contexts and the varied pedestrian and roadside environment. The designer should examine the available speed range to select the operating speed most appropriate for all users given the facilities and context.
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Decision-Making Steps Within the Suggested Speed Limit Procedure 15 Speed Distribution The distribution of individual vehicle speeds within the traffic stream is dependent on several factors. Speeds tend to be relatively uniform (i.e., narrowly distributed)
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16 Posted Speed Limit Setting Procedure and Tool: User Guide When the roadway conditions are optimal, the suggested speed limit would reflect the 5-mph increment closest to the 85th percentile speed except for segments within the Full- Access SLSG, where it would reflect the 5-mph increment closest to the 50th percentile speed in recognition of the anticipated users within those facilities. When roadway conditions are not favorable to all users or when crashes are a significant concern, then the suggested speed limit would reflect the 5-mph increment closest to the 50th percentile speed for Limited-Access, Developed, or Undeveloped SLSGs or the 5-mph increment rounded down from the 50th percentile speed for the Full-Access SLSG.
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Decision-Making Steps Within the Suggested Speed Limit Procedure 17 unusual but are accurate given the provided speed data, and hence should be interpreted with caution. Decision Rules for Each Speed Limit Setting Group The following sections presents the decision rules for selecting the 5-mph increment that reflects C50, RD85, or C85 by SLSGs.
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18 Posted Speed Limit Setting Procedure and Tool: User Guide Speed Limit Setting Group: Developed Table 7 provides an overview of the variables along with the variable value that would trigger using C85, RD85, or C50. Table 8 provides the decision matrix for sidewalk presence/width, sidewalk buffer, and pedestrian activity combinations for Developed SLSG.
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Decision-Making Steps Within the Suggested Speed Limit Procedure 19 Variable Closest 50th (C50) Rounded-Down 85th (RD85)
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20 Posted Speed Limit Setting Procedure and Tool: User Guide Pedestrian Activity Sidewalk Presence/Width Sidewalk Buffer SpeedPercentage High Adequate Not present RD50 High Adequate Present C50 High Narrow Not present RD50 High Narrow Present RD50 High None Not applicable RD50 High Wide Not present C50 High Wide Present C50 Some Adequate Not present RD50 Some Adequate Present C50 Some Narrow Not present RD50 Some Narrow Present RD50 Some None Not applicable RD50 Some Wide Not present C50 Some Wide Present C50 Negligible Adequate Not present C50 Negligible Adequate Present C50 Negligible Narrow Not present C50 Negligible Narrow Present C50 Negligible None Not applicable C50 Negligible Wide Not present C50 Negligible Wide Present C50 See text for additional discussion on sidewalk presence/width and sidewalk buffer characteristics. Table 10.
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