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1 CHAPTER 1 INTRODUCTION AND RESEARCH APPROACH PROBLEM STATEMENT AND each individual supplementary sign such as chevrons; then RESEARCH OBJECTIVE progress with combinations of supplementary signs, adding striping, post-mounted delineators, raised pavement markers, The appropriateness and effectiveness of traffic control and so on. The number of treatments to be tested alone would devices (TCDs) used to inform drivers of the presence of, and have numbered in the dozens. Then, curve characteristics such appropriate speed for, horizontal curves remains a subject of as geometric characteristics, presence and absence of inter- interest to researchers; to practicing engineers at federal, state, sections or driveways in and near the curve, and parameters and local levels; and, most importantly, to the motoring pub- such as design speed for the curve would have to be varied. lic. While horizontal curves in general have long been iden- This would result in a test matrix with hundreds of cells. tified as high hazard locations, many of these curves are per- Given the number of combinations, the use of field studies ceived as "simple" highway situations by drivers while others to develop universal and explicit guidelines for use of selected stand out as very hazardous. Many of the previous studies TCDs was prohibitive in terms of time and funds available. of horizontal curves have identified inconsistencies in using Thus, this research relied on focus groups and surveys aug- TCDs to convey the appropriate message to the driver as an mented with limited and more qualitative field work. With the issue. For example, how severe is "this" curve? What driver exception of the field work, most of the project activities made action is required here? In this context, the underlying objec- use of participants/respondents ranging from national samples tives of this research were to develop guidelines regarding to groups from two states; the latter included drivers from when and how to communicate horizontal curve information Michigan and North Carolina. to drivers in a credible, effective, consistent, and timely man- ner. This includes recommendations for changes to the Man- RESEARCH APPROACH ual on Uniform Traffic Control Devices (MUTCD). It should be noted that "TCDs," in this context, is meant to include all The project included the following tasks: traffic control devices such as advisory signs, advisory speed · A traditional literature review; plaques, regulatory signs, pavement markings, and delineators. · Focus group exercises involving practitioners from However, the emphasis that emerged was on signing. four states and two jurisdictional levels, state DOTs, and county road engineers; SCOPE OF STUDY · A nationwide survey of practitioners; · Focus group exercises involving crash-involved and The original scope of the study was fairly unrestricted in terms typical or "average" Michigan drivers; of curves and types of TCDs, but as the project progressed, the · A survey of crash-involved and typical or "average" scope changed. The types of roads were reduced to an empha- drivers in Michigan and North Carolina; sis on two-lane, two-way rural roads with a "client" who was · A limited field study of behavior as Michigan drivers more likely to be practicing at the county-road or similar level. negotiated a pre-determined route and encountered var- Thus, while some attention was given to the full range of TCDs ious horizontal curves; including "high-tech" solutions such as speed-triggered sign · Development of recommendations for changes in the messages or flashing lights, the emphasis was on more routine MUTCD; and treatments likely to be used by lower-budget jurisdictions. · A final nationwide survey of practitioners to assess the In order to develop comprehensive guidelines for the use of perceived need for, and practical utility of, the recom- various TCDs in different horizontal curve situations, a full- mendations. factorial experiment design matrix would have been necessary that would have considered the permutations and combinations REPORT ORGANIZATION of TCDs and site conditions. For example, the treatments to be tested would start out with stand-alone applications of the basic In the remainder of the report, summaries of findings from curve signs; then progress to those signs in combination with each of the tasks listed above are presented.