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17 the purpose of deciding upon the applicability, design, oper- not surprisingly, there is no attribution of the reasons for the ation, or installation of a traffic control device. Engineering inconsistencies. judgment shall be exercised by an engineer, or by an indi- Practitioners were generally in favor of the concept of better vidual working under the supervision of an engineer, through the application of procedures and criteria established by the guidelines for using TCDs that would lead to more consistent engineer. Documentation of engineering judgment is not use, but there was an even stronger sentiment for maintaining required. sufficient flexibility for rendering judgments regarding which devices should be used when. However, practitioners expressed It is not surprising that there are inconsistencies in the use concern about prescriptive guidelines that could be interpreted of TCDs to communicate information on changes in hori- as what "must" be done. zontal alignment to the driver because the MUTCD does not In this context of varying views of what the content of specify or even suggest factors to be considered when apply- guidelines could or should consist of, a set of recommendations ing engineering judgment in this instance. was developed. In the paragraphs that follow several rela- tively modest changes to the MUTCD (the millennium edition FINDINGS FROM THIS STUDY version) are recommended based on the results of the research RELATED TO UNIFORMITY presented here. These changes were then presented to prac- titioners in a survey. The response to the survey is contained The driver survey respondents and the driver focus group in the following section of this report. participants in this study both reported a perception of non- uniform treatment of horizontal alignment changes across different jurisdictions. The practitioner survey results included RECOMMENDED CHANGES TO THE MUTCD the finding that in many jurisdictions the decisions on which, if First Change any, TCDs to use to inform the driver of a change in horizontal alignment are made by non-engineers. The participants in the Recommended Change practitioner focus groups identified the need for better guidance on when to use supplemental TCDs at horizontal curves. The first recommended change is as follows (changes to The practitioner survey revealed a wide variation in the use the language of the MUTCD are in bold): of chevrons: from using them on all curves when an advisory speed plaque is used to only using them when there is a 6 or 1. The first option in 2C.06 of the MUTCD should be greater degree of curvature. The DPM study was inconclusive changed to read horizontal alignment signs may be used with respect to using chevrons because they did not seem to in advance of situations where the roadway alignment change driver performance when negotiating curves. changes The practitioner survey also revealed a wide variation about the decision of when to use advisory speed plaques: some and should be used when the alignment change would result jurisdictions use them on all curves when the advisory speed is in an advisory speed equal to or lower than the posted speed equal to or less than the posted speed limit but other jurisdic- limit. tions use them on curves where the advisory speed is 20 mph The Winding Road (W1-5) sign should be used where there or more below the posted speed limit. This variation could is a series of turns or curves that requires driving caution be problematic because the driver survey respondents and and where curve or turn signs would be too numerous to be the driver focus-group participants both stated that they use effective. Where any of the curves has an advisory speed that the advisory speed as a guideline in selecting the speed when is (X) mph or more below that of the first curve, then a curve or turn warning sign and an advisory speed plaque should entering a horizontal curve. The latter is in spite of the fact that be used. they do not necessarily slow to the posted advisory speed. Overall, the TCD options provided in the MUTCD are per- ceived to be adequate--there does not appear to be an unmet Bases for the Recommendation demand among practitioners for a range of new and different options. Likewise, drivers seem reasonably satisfied with the The bases for the first recommendation are as follows: TCDs that they encounter and, in fact, place TCD changes relatively far down a list of changes they would like to see at The state MUTCD review showed that at least 10 states horizontal curves. In a similar vein, most practitioners stated have already adopted this language. that they use TCDs consistently although they are not so sure The practitioner survey indicated that horizontal align- about their counterparts in other jurisdictions. ment signs are already widely used except on winding Practitioners were likely to attribute inconsistency in the use roads and low-volume roads, which are covered in sep- of TCDs to differences in operating budget and other resources arate sections of the MUTCD. and not to interpretation of the manual. Drivers also perceive This change would increase uniformity at a relatively low some inconsistency from one jurisdiction to another although, cost because most agencies already sign those curves