Communicating Changes in Horizontal Alignment (2006) / Chapter Skim
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Pages 23-28
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From page 23... ...
First Recommendation (Changing "May" to "Should" Regarding Use of Basic Curve Signs) The text of the first recommendation and the results regarding "adoption" are shown in Table 2.
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Somewhat surprisingly, there were only a few comments, and they were mixed -- for example, define X or options should always use "may." Third Recommendation (Engineering Study) Although the requirement for the use of an "engineering study" is cited in the MUTCD, the term is not adequately First recommendation: The first option in §2C.06 of the millennium edition of the MUTCD should be changed to read that horizontal alignment signs may be used in advance of situations where the roadway alignment changes and should be used when the alignment change would result in an advisory speed equal to or lower than the posted speed limit.
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Just less than 22 half thought that the list was adequate "as is" with the rest desiring to modify the list in some way -- primarily by adding factors. Table 6 is the distribution of responses to a follow-up question regarding the factors that should be included in an engineering study to determine the appropriate TCDs for horizontal curves.
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If answered "yes" regarding adoption of a recommendation for an engineering study for TCD applications at horizontal curves, is the list of factors sufficient? Employer Possible Responses county road commission (n=37)
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-- 2 85th-percentile (part of above, but listed separately as several wanted to eliminate reference to this speed) -- -- 5 the approach sight distance to the beginning of the curve 37 -- 3 the visibility around the curve 37 -- 3 unexpected geometric features within the curve, such as an intersection or a change in the curve radius 37 -- 1 the position of the most critical curve in a sequence of relatively closely spaced curves 37 -- 2 shoulder width -- 2 -- shoulder type -- 1 -- obstruction close to pavement -- 1 -- gradient -- 2 -- ball-bank study -- 5 -- ball-bank study using 10° -- 1 -- electronic ball-bank study -- 1 -- 85th-percentile speed of vehicles in curve -- 1 -- accident history -- 7 -- superelevation -- 1 -- roadway volume or average daily traffic -- 3 -- signing practices in area -- 1 -- degree of curvature -- 1 -- TABLE 6 Factors suggested for inclusion in horizontal curve study
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From page 28... ...
* state highway department (n=62)
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