Communicating Changes in Horizontal Alignment (2006)

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