Posted Speed Limit Setting Procedure and Tool: User Guide (2021) / Chapter Skim
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Pages 44-50
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From page 44... ...
44 Why 85th or 50th Percentile Speed? Currently, the predominant method for setting speed limits is with the use of the 85th percentile speed.
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From page 45... ...
Other Considerations When Setting Posted Speed Limits 45 For the SLS-Procedure, the research team suggested the consideration of measured operating speed as the starting point for selecting a posted speed limit, but that the measured operating speed be adjusted based on roadway conditions and the crash experience on the segment. Identifying the Segment Limits Roadway segments are defined based on roadway characteristics and roadway context and type.
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From page 46... ...
46 Posted Speed Limit Setting Procedure and Tool: User Guide along its length, and record keeping for the roadway will be more complex. If the roadway has a large number of short segments, it may be necessary to combine adjacent segments that are reasonably similar or apply speed limits from adjacent segments to the segment of interest, if appropriate.
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From page 47... ...
Other Considerations When Setting Posted Speed Limits 47 Design Speed The relationship between design speed and posted speed was addressed in a 2015 memorandum from FHWA (46)
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From page 48... ...
48 Posted Speed Limit Setting Procedure and Tool: User Guide can be affected by whether the section is undivided or divided. The effect of this variable on crash frequencies differs based on the facility type.
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From page 49... ...
Other Considerations When Setting Posted Speed Limits 49 TCD Variables The type of TCDs present can influence operating speeds and crashes. For example, when traffic signals are timed to optimize progression along a corridor, drivers tend to operate at that speed to avoid having to stop at the next signal.
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From page 50... ...
50 Posted Speed Limit Setting Procedure and Tool: User Guide • Other roadway geometry variables: Other roadway geometry variables that may have an effect on speed or crashes include the LW, number of lanes, presence of bike lane, intersection angle, and intersection lighting. Variables Associated with Roadway Surroundings The characteristics of the road's surroundings, including the neighboring land use, affect both operating speed and crashes.
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