NCHRP Project 3-61 examined the use of traffic control devices (TCDs) for communicating changes in the horizontal alignment of roadways. Although the initial scope had been fairly broad, the emphasis that emerged was on two-lane, two-way rural roads. The objective was to develop guidelines and/or recommendations for the consistent and uniform use of TCDs for horizontal curves. Activities included a literature review; focus group exercises involving practitioners in Michigan, North Carolina, and Indiana with some supplemental interviews of other practitioners in North Carolina and Tennessee; a nationwide survey of practitioners; focus groups with drivers in Michigan; a survey of crash-involved and typical drivers in Michigan and North Carolina; a field observation study of 40 drivers in Michigan, including three “expert” drivers from the Michigan State Police; and a final nationwide survey of practitioners to assess their response to proposed changes to the Manual on Uniform Traffic Control Devices (MUTCD). 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 horizontal 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 practitioners consulted, it became clear that with limited resources, it would be impossible to develop comprehensive guidelines for use of different TCDs in myriad combinations of circumstances. Finally, most practitioners felt that existing guidelines and engineering judgment were adequate for determining when different devices should be used. Thus, the suggested changes in guidelines became more general, and even those were subject to debate. For example, while something as straightforward http://gulliver.trb.org/publications/nchrp/nchrp_rpt_559.pdf This report may be accessed by Internet users at as changing the language from “may” to “should” in warning signs was supported by a significant majority of practitioners, there was still substantial opposition. Thus, it is unlikely that widespread support for more explicit guidelines would be well received. (Author/publisher)
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