Communicating Changes in Horizontal Alignment (2006)

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26 CHAPTER 5 REVISED RECOMMENDATIONS FOR THE MUTCD AND RELATED CHANGES INTRODUCTION In this chapter, revised recommendations are presented. The revisions are prompted by two things: (1) the responses of practitioners to the originally proposed recommendations and (2) the reconciliation of the changes to the MUTCD that are needed because of the differences between the millennium and 2003 editions of the MUTCD. It is again noted that the proposed changes to the MUTCD are modest in scope. This is due to several reasons: the results from the study indicated that the basic guidelines for using curve-related TCDs are not seriously “broken” and do not need major revision; results from this project, as well as more spe- cific results from previous work, are sometimes inconsistent; it is virtually impossible to develop guidelines that would apply to all situations and still be explicit (e.g., if a speed reduction of X is desired, use sign Y with chevrons and centerline markings); and, perhaps most importantly, most practitioners have mixed feelings regarding more explicit guidelines. Concerning the latter, there was some resistance to even listing elements of what should be considered in an engineering study, let alone providing guidelines regarding how the results of such a study would be interpreted to determine the appropriate TCDs for a given horizontal curve. In the paragraphs that follow, the three basic recommenda- tions are reiterated and discussed individually. In each instance, the original recommendation is presented and then discussed. FIRST RECOMMENDATION Initial Proposed Statement The initial proposed statement is as follows: 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. The Winding Road (WI-5) sign should be used where there is a series of turns or curves that requires driving caution and where curve or turn signs would be too numerous to be effec- tive. Where any of the curves has an advisory speed that is (x) mph or more below that of the first curve then a curve or turn warning sign and an advisory speed plaque should be used. This recommendation had good support from the practitioners in the follow-up survey. Exceptions to this came from prac- titioners who interpreted the “may to should” as a rule that must be followed with at least one state indicating that this is the way that a state attorney general had interpreted it. Given that states have the option of adopting the MUTCD in a whole- sale manner or with exceptions, states that have significant problems with the language can make an exception. These problems notwithstanding, most respondents indicated that they were supportive of the change. Existing Statements in the MUTCD The precise wording of the first option in §2C.06 of the millennium edition (ME) and 2003 edition are shown below with additions in the 2003 version shown in italic: • ME: The horizontal alignment Turn (W1-1), Curve (W1-2), Reverse Turn (W1-3), Reverse Curve (W1-4), or Winding Road (W1-5) signs may be used in advance of situations where the horizontal roadway alignment changes. A Large Arrow. . . . • 2003: The horizontal alignment Turn (W1-1), Curve (W1-2), Reverse Turn (W1-3), Reverse Curve (W1-4), or Winding Road (W1-5) signs (see Figure 2C-1) may be used in advance of situations where the horizontal roadway alignment changes. A One-Direction Large Arrow. . . . The messages regarding use of the noted signs are basically the same in both of these versions with only clarifying comments added. Final Proposed Statement The proposed revised version that results from implement- ing the first part of the first recommendation, using the 2003 version as the base and showing changes in bold, is as follows: The horizontal alignment Turn (W1-1), Curve (W1-2), Reverse Turn (W1-3), Reverse Curve (W1-4), or Winding Road (W1-5)

signs (see Figure 2C-1) may be used in advance of situations where the horizontal 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. A One-Direction Large Arrow. . . . The Winding Road (W1-5) sign should be used where there is a series of turns or curves that requires driving caution and where curve or turn signs would be too numerous to be effective. Where any of the curves has an advisory speed that is 10 mph or more below that of the first curve, then a curve or turn warning sign and an advisory speed plaque should be used. The speed of 10 mph is inserted in the second paragraph above based on the responses to other questions in the final survey. This is also discussed below. An additional question, chang- ing the “should” condition to “shall” had very little support because as it was apparently interpreted as potentially caus- ing too many liability or litigation-related problems and being too prescriptive. Thus, the more emphatic language is not recommended. SECOND RECOMMENDATION Initial Proposed Statement Section 2C.42 of the MUTCD should be changed to read: An Advisory Speed (W13-1) plaque should be used to indicate the advisory speed for a change in horizontal alignment when the advisory speed is X mph or more below the applicable speed limit. This recommendation also garnered good support although the objections from some respondents were basically the same as reported for the first recommendation. Existing Statements in the MUTCD In the ME, the discussion of advisory speed plaques was in §2C.42. In the 2003 edition, this discussion was in section §2C.46. The precise wordings of these two versions are given below with changes in the 2003 edition shown in italic: • ME (§2C.42): The Advisory Speed (W13-1) plaque may be used to indicate the recommended speed for a condition. • 2003 (§2C.46): The Advisory Speed (W13-1) plaque (see Figure 2C-5) may be used to supplement any warning sign to indicate the recommended speed for a condition. While one of the changes between the ME and 2003 edition is merely a clarifying comment, the other change is potentially more sweeping—referring to all instances where the plaque is used to supplement a warning sign. The earlier version also had general application but it was placed in the section with 27 the horizontal curve signs. The wording that had been proposed here and reviewed by the practitioners referred explicitly to horizontal curves and not all instances where advisory speed plaques might be used. Final Proposed Statement The final proposed revision is for a new section that would be applicable only to horizontal curves and based, in part, on the 2003 wording is as follows: An Advisory Speed (W13-1) plaque should be used to indicate the advisory speed for a change in horizontal alignment when the advisory speed is 10 mph or more below the applicable speed limit. Another option is to replace §2C.46 in the 2003 edition with a variation on the wording given above—that is, to eliminate the words “for a change in horizontal alignment” thus making the proposed revision more generic. As was the case for the first recommendation, the speed of 10 mph is inserted in the proposed revision above based on the responses to other questions in the final survey. The selection of “10” as the speed increment to be used is based on the final survey responses and consistent with general comments from drivers and practitioners during the focus group and earlier survey exercises. The possibly more significant addition to the section on advisory speed plaques in 2003 was the “option” section where the advisory speed was defined: The advisory speed may be the 85th percentile speed of free- flowing traffic, the speed corresponding to a 16-degree ball bank indicator reading, or the speed otherwise determined by an engineering study because of unusual circumstances. It is also noted that the first two conditions are thought to be approximately equal for horizontal curves. This definition for determining appropriate advisory speeds has the potential to significantly increase existing advisory speeds and to have adverse impacts on motorist speeds through horizontal curves. The latter occurs if motorists continue to assume that they can travel at speeds that are typically as high as “+10 mph” over the posted advisory speed. If the advisory speed is “set” at a speed approximating the 85th-percentile speed, the aver- age motorist may actually exceed what would be the normal 85th-percentile speed by 5 to 10 mph or more. That is, they might maintain what they perceive to be a safe increment over the posted advisory. While the higher advisories may be “more realistic,” motorist reaction is not clear and it is like- wise not clear how the revised guidelines might be phased in within and between jurisdictions. At least in the short term, the lack of consistency among speed advisory applications may be exacerbated rather than ameliorated by exercising the new option. Based on responses to the survey questions, it seems likely that practitioners would be critical of this option in terms

28 of it costing a considerable amount of money to re-check all existing curves within a jurisdiction and in terms of increased liability, at least during a transition period. Some jurisdictions may also selectively not adopt this definition, resulting in long-term differences between jurisdictions—that is, less consistency, not more. THIRD RECOMMENDATION Initial Proposed Statement Add a section to the MUTCD (similar to section §2B.11 for setting speed limits in speed zones) to define the factors to be considered when conducting an engineering study to establish the appropriate TCDs when there is a change in the horizontal alignment of the highway. The language should read as follows: Standard: After an engineering study has been made in accordance with established traffic engineering practice or where engineering judgment determines the need for horizontal alignment signs, advisory speed plaques, and/or supplemental guidance, these TCDs shall be used. Guidance: The factors that should be considered in determining the system of TCDs to be displayed when there is a change in the horizontal alignment of the highway include the following: • The difference in the posted speed limit and the 85th- percentile speed of free-flowing traffic; • The approach sight distance to the beginning of the curve; • The visibility around the curve; • Unexpected geometric features within the curve, such as an intersection or a change in the curve radius; and • The position of the most critical curve in a sequence of relatively closely spaced curves. In the 2003 edition, the section on speed limit signs was renumbered (from §2B.11 in the ME to §2B.13 in the 2003 edition) although the content remained basically the same. As noted, the factors to be considered in an engineering study are not explicitly defined in either the ME or 2003 edition. How- ever, in both editions, there are factors implied in the guidance section on the use of the advisory speed plaque (ME §2C.42; 2003 edition §2C.46): Because of changes in conditions, such as roadway geo- metrics, surface characteristics, or sight distance, might affect the recommended speed, each location should be periodi- cally evaluated and the Advisory Speed plaque changed if necessary. In this context, defining the factors that should be considered in an engineering study doesn’t really increase the level of obligation for a jurisdiction doing studies or periodic evalu- ations but rather provides a list of the factors to be considered. However, based on the results from the final practitioner sur- vey, the list of factors initially proposed has been modified in the final proposed statement given below. Final Proposed Statement Changes from the initial statement are shown in italic: Standard: After an engineering study has been made in accordance with established traffic engineering practice or where engineering judgment determines the need for horizontal alignment signs, advisory speed plaques, and/or supplemental guidance, these TCDs shall be used. Guidance: The factors that should be considered in determining the system of TCDs to be displayed when there is a change in the horizontal alignment of the highway include • The difference in the posted speed limit and the 85th- percentile speed of free-flowing traffic (or a 16° ball-bank reading); • The approach sight distance to the beginning of the curve; • The visibility around the curve; • Unexpected geometric features within the curve, such as an intersection or a change in the curve radius; • Curve and roadway geometry; • Accident history; and • As appropriate, the position of the most critical curve in a sequence of relatively closely spaced curves. It is also recommended that further definition of the factors to be included in engineering studies related to horizontal curves be included in appropriate sections of the Traffic Control Device Handbook. It has been argued here that the existing definition of an “engineering study” is too general for the purposes of placing TCDs on horizontal curves; it is thus recommended that the inclusion of a more explicit list of factors to be considered be included in the definition. The current definition does little to help practicing engineers know what to look at when under- taking such a study. Indeed, there are other instances in the MUTCD where additional factors to be considered in other situations are explicitly listed. For example, in §2B.13 regard- ing speed limit signs, six factors are listed including road char- acteristics, pace speed, roadside development and environment, parking practices and pedestrian activity, and crash experience. Signal and other warrants are also, in essence, lists of factors to be considered in engineering studies. In addition, just under two-thirds of county road and DOT respondents to the final survey regarding the efficacy of the suggested recommenda- tions thought this recommendation should be adopted.

It has also been recommended that these changes should be in the MUTCD as recommended because not all engineers and other persons determining which TCDs to use at a hori- zontal curve necessarily have ready and immediate access to other references such as the TCD Handbook. Nonetheless, the expanded list of factors to be included should also be included in the TCD Handbook along with a recommended procedure for collecting the various data. FOURTH RECOMMENDATION Initial Proposed Statement The initial proposed statement is as follows: NCHRP should consider funding a project to incorporate these factors in an expert system similar to the U.S. Limits system being developed to provide guidance on the speed limit to be posted in speed zones. The response of the practitioners to the proposed expert system was not as positive as had been expected. However, based on some respondent comments, at least some of the opposition can be attributed to the respondents not knowing enough about such a system. Moreover, it is neither intended that development of such a system nor use of it be linked directly to the MUTCD. A problem for which there is variation among the opinions of different professionals and for which there is no precise set of rules or algorithm that can be used to produce a “right” answer is a problem for which an expert system is expected to have application. There is also value in linking development of an expert system to outcomes and experience gained through implemen- tation of the third recommendation—that is, if studies for horizontal curves become more the norm, valuable information should be obtained by practitioners that ultimately assists them in making more informed decisions regarding TCD treatments and specifying speed advisories for those locations. This experience will also be helpful in developing and refining expert systems. Final Proposed Statement The recommendation for development of such an expert system is still advanced although the proposed statement is modified: NCHRP should consider funding a project to develop an expert system that would incorporate the factors listed in the third recommendation and that would be used for guidance for traffic control device deployments (including advisory speeds) for horizontal curves. Information and experience obtained as a result of the implementation of the third recommendation should also be incorporated into the system. This system should be similar in concept to the U.S. Limits system being developed to provide guidance on the speed limit to be posted in speed zones. 29 CONCLUDING REMARKS Initially, the outcomes of this project had been envisioned to include a comprehensive set of guidelines for using various TCDs, including advisory speed plaques, for changes in hor- izontal alignment on different components of the road system. Over time, the emphasis changed to two-lane, two-way rural roads. Moreover, as the literature was reviewed and practi- tioners consulted, it became clear that it would be impossible with limited resources to develop comprehensive guidelines for use of different TCDs in the myriad combinations of cir- cumstances that exist in the field, for example: Under what explicit circumstances should chevrons be used? What would the expected result be? Finally, most practitioners felt that existing guidelines and engineering judgment were adequate for determining when different devices should be used. An interesting conundrum was presented by the responses from road users, from practitioners, and even from the NCHRP panel. While there is general agreement that improving con- sistency in the application of the various TCDs available to provide information and guidance to drivers encountering a change in horizontal alignment is desirable, there is significant reluctance to support language or guidelines that would result in this improved consistency. Moreover, as just noted, it is not clear that specific guidelines applicable to each of the myriad combinations of factors related to horizontal curves could ever be realized. The MUTCD already contains language recognizing that there may be an exception to any standard, guidance, or option when engineering judgment determines that the situation can be made safer or can operate more efficiently if an exception is used (i.e., §1A.09 in the 2003 edition). However, the for- mulation of standards and guidance can be effective tools in achieving uniform application of TCDs. Since horizontal curves are so numerous and varied, some guidance can none- theless be an effective means of reducing the inconsistent use of these devices, an inconsistency that is recognized by the engineering community. If more explicit standards or guidance are not acceptable to many practitioners and/or if it is impossible to develop an exhaustive set of guidelines, the alternative should be to improve consistency in the exercise of engineering judgment by identifying the factors that should be considered in deter- mining the appropriate treatment. If all engineers consider the same factors in making a decision, there is an increased prob- ability that they will reach the same decision for a given set of conditions, thus leading to greater uniformity. Conversely, uniformity will not be achieved by allowing engineers and non-engineers to continue to select the TCDs to be used on horizontal curves without guidance or even the identification of factors that should be used in making these decisions. Thus, the suggested changes in guidelines became more general, and even those were subject to debate. For example, while something as straightforward as changing from “may” to “should” for the use of warning signs was supported by a

30 The recommendations for additional research come in two areas. The first area is the need for the investigation of devel- opment of an expert system. Because of the combinations of conditions encountered in the field, an expert system would seem to represent a viable tool to be used by engineers in assessing the need for different TCDs at specific locations. Used properly, it would help engineers identify the options that “best practices” might indicate for TCDs at an explicit site. The second area is further research into motorist reaction to wholesale changes in determining the appropriateness of advisory speeds using a ball-bank reading of 16°. Based on feedback from both motorists and practitioners, it is important to ascertain how motorists will respond to what will generally be higher advisory speed values on many curves. If motorists, and especially “unfamiliar” ones, continue to routinely exceed the new speed advisories by the same margins as they do now, dangerous situations could easily exist. Moreover, it is expected that “conversion” to a new method would lead to considerable inconsistency in the use of advisory speed plaques for several years. This would occur, if for no other reason, because of the apparent disparities in budgets of different county road com- missions, resulting in some counties, states, or parts of states “converting” their advisory speed plaques immediately while others lag for several years until the advisory speed plaque and other curve-related TCDs might otherwise be updated as a part of normal maintenance. significant majority of practitioners, there was still substantial opposition. It is unlikely that widespread support for more explicit sign-specific guidelines would be well received. Thus, the suggested changes to the MUTCD were modest in some respects. However, they were all directed to providing more consistent information to the motorist. Nonetheless, from other perspectives even these changes were cause for consternation. Finally, there was a comment regarding whether the existing arsenal of TCDs available for horizontal curves is “working.” The United States has a crash rate that is among the lowest in the world, and the crash rate has decreased substantially over time. This decrease is due to good traffic engineering practice, among other things, and points to how well the sys- tem does work, not that it couldn’t improve. If anything, this research project demonstrated that the TCD arsenal readily available to practitioners is actually working well. In addition, most of the practitioners that participated in the project were satisfied with the array of available TCDs and the “instructions” for using them. For the most part, and including recommen- dations made here, changes that are required are “tinkering at the margin.” If the expectation was for radical changes to the MUTCD, then the outcomes here are disappointing. However, if the desire was to obtain a reasonable assessment of whether things needed to be changed, then that has been achieved— and the required changes are minimal.