Development of a Posted Speed Limit Setting Procedure and Tool (2021) / Chapter Skim
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Pages 43-52
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From page 43... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 31 APPENDIX B RELATIONSHIP AMONG ROADWAY CHARACTERISTICS, SPEED, AND SAFETY FOR HIGH-SPEED HIGHWAYS Several factors are known or suspected to affect safety on rural or high-speed highways, such as horizontal/vertical alignment, shoulder width, passing zone and passing lane presence, and access point density.
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From page 44... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 32 Operating Speed Relationship with Crashes A study using 179 roadway sections in Israel explored the relationship between free-flow speeds (obtained from GPS devices) and crashes on rural, two-lane highways with a typical speed limit of 50 mph (9)
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From page 45... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 33 Posted Speed Limit Relationship with Operating Speed For rural high-speed highways, posted speed limits are typically established by taking several factors into consideration, including the roadway design speed. Vehicular operating speeds along tangent sections of two-lane highways have been shown to be impacted by the posted speed limit, with vehicular speeds increasing as the posted speed limit increases (123, 124, 118)
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From page 46... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 34 Passing Lane Relationship with Operating Speed Freedman and Kaisy (137) investigated the passing maneuvers within a passing lane section on a rural two-lane, two-way highway located on a U.S.
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From page 47... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 35 Vertical Alignment Relationship with Crashes Prior research has shown that steeper vertical alignments could induce higher crash potentials (16, 123)
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From page 48... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 36 Median Relationship with Operating Speed A study on rural four-lane highways in Kentucky (155) found that the presence of a median barrier is related to operating speed.
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NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 37 Lane Position Relationship with Operating Speed Himes and Donnell (121) measured different speeds in the left and right lanes for rural and urban four-lane highways and identified the following variables as relevant to their study: heavy vehicle percentage, posted speed limit, and adjacent land use.
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From page 50... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 38 speeds, so vehicles close to each other, which could happen at a driveway access point, were removed. Urban or Rural Relationship with Crashes Whether the roadway segment is in a rural area or an urban area has been found to be significantly related to crashes (115)
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From page 51... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 39 Table 3. Factors of high-speed highways that affect crashes.
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From page 52... ...
NCHRP Web-Only Document 291: Development of a Posted Speed Limit Setting Procedure and Tool 40 Table 4. Factors of high-speed highways that affect operating speed.
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