Development of a Posted Speed Limit Setting Procedure and Tool (2021) / Chapter Skim
Currently Skimming:
Pages 107-118
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 107... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 95 APPENDIX E RELATIONSHIP AMONG URBAN/SUBURBAN ROADWAY CHARACTERISTICS, POSTED SPEED LIMIT, AND CRASHES IN WASHTENAW COUNTY, MICHIGAN OVERVIEW In order to provide guidance for the setting of speed limits consistent with the stated objectives of NCHRP Project 17-76, a safety analysis was conducted specific to urban and suburban roadway segments located in Washtenaw County, Michigan (see Figure 17)
|
From page 108... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 96 then reduced to include only non-freeway and non-local roadways with urban designations where the posted speed limit ranged between 25 to 50 mph. These candidate roadways were then segmented such that each roadway segment's end points were intersections controlled via either signalization, stop control, a roundabout (yield control)
|
From page 109... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 97 Council of Government's (SEMCOG's) open data portal (217, 218)
|
From page 110... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 98 A map of study segments by posted speed limit is presented in Figure 21, and a map of study segments by AADT is presented in Figure 22. Figure 20.
|
From page 111... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 99 Figure 22. Study road segments by AADT estimate.
|
From page 112... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 100 Additional Geometric and Roadway Characteristics After the identification of the study road segments, an additional manual review of satellite imagery was performed in order to collect a variety of geometric and other roadway characteristics specific to each segment. These characteristics are summarized in Table 39.
|
From page 113... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 101 DATA ANALYSIS -- METHODOLOGY The research team compiled the dataset consisting of 530 sites to conduct the analysis. Table 40 provides the descriptive statistics for the variables considered in the analysis.
|
From page 114... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 102 RESULTS AND DISCUSSION Variable Relationships with Crashes The investigation into the relationships among the roadway characteristics, posted speed limit, and traffic crashes focused on segment crashes rather than all crashes that included intersections. The research team considered both crashes with fatal and injuries (i.e., KABC)
|
From page 115... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 103 Table 42. Variables with significant effects on KABC segment crashes.
|
From page 116... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 104 Median type was significant for all severity level crashes, with the presence of a raised median being associated with fewer crashes than either a TWLTL or no median, which is consistent with the findings for data from Austin. The presence of a TWLTL was also associated with fewer crashes when compared to no median, a finding that is contradictory in this case to the KABC NID crash data from Austin.
|
From page 117... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 105 Variable Relationships with Posted Speed Limit A better understanding of relationships between roadway characteristics and the posted speed limit may assist with identifying how the look and feel of a road could help to communicate the appropriate operating speed along with the posted speed for the facility. Table 45 provides a summary of three models that explore the significance for several variables with posted speed limit.
|
From page 118... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 106 Table 45. Models exploring the significance of variables for posted speed limit.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.