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14 visibility through the curve, was more problematic. The con- other parts of this project where surveyed drivers re- clusion, albeit based on only two sequences, is that drivers will ported that they consistently exceed posted advisory generally perform well unless a curve is more difficult. This speeds at curves and where practitioners indicated that gives credibility to the idea that gravel roads may require less their expectations and perception of common practice signing except at difficult curves such as those that require a were that drivers routinely exceeded advisories. This turn arrow, have sight distance problems, or both. Again, the phenomenon is also noted in the literature review. sample size of curves in this category is quite small. Raising advisory speeds may well result in drivers who routinely exceed advisories and approach the maximum safe speeds, at least in the short term. Moreover, the Curves and Intersections problem will likely be worse on curves with the lowest advisories. Thus, the effects of driver response to raised Results from other parts of this project have also indicated advisories should be thoroughly studied before changes that more problematic types of curves are those that have are made. additional distractions or elements--most specifically, an It is not clear that comprehensive signing for curves intersection either on or near the curve. The speed differen- needing the lowest speed advisories will reduce the tials notwithstanding, the problems that drivers had in sev- number of drivers with errors. However, the number of eral sequences were in not giving adequate attention to the problems with such curves suggests that drivers either intersection that was encountered in the vicinity of the curve need additional information or need to better process in spite of the fact that standard intersection signs were typ- and/or respond to the information that is made available. ically present. There were six sequences (5, 11, 3, 7, 8, and Thus, it is argued that signing should be comprehensive 5a) that had an intersection or, in one instance, a driveway for the situations where the lowest advisory speeds are that was in essence an intersection. The two sequences that appropriate. had the most intersection-related errors were 5 and 5a where the intersection was literally on the curve: 10 and 25 drivers, respectively, made errors. In these two sequences the inter- General Speed-Related Issues secting roadway came in at close to a right angle from one side or the other. Three other sequences (11, 3, and 8) had A recommendation regarding speed-related issues is as intersections close to, but not on, the curve. These intersec- follows: tions were far less problematic with between one and four drivers making errors. The final sequence of interest (7) had The recommendation for the sequences where the initial an intersection in the curve, but drivers had an excellent view speed is relatively high but decreases at a subsequent of it as the intersecting road was essentially "straight ahead" curve within a series of relatively close curves is to con- as they approached it and the road (and route) curved to the tinue to sign the lower-speed curve aggressively in spite left--a significantly different "look" for the approaching of the number of drivers making errors even when speed driver. Notwithstanding the fact that all of these intersections advisories and other treatments are present. This is con- were marked with Intersection Ahead signs, it is clear that sistent with current practice of independent signing for intersections in the curve caused the most difficulties for sequential curves unless the tangent is <600 feet long. drivers. None of the signs "combined" the curve and inter- section warning. Given the problems experienced, even with signs deployed, it seems clear that the combination is indeed Driver Errors problematic and that drivers should be provided with advance warning whenever possible. Findings and recommendations regarding driver errors are as follows: Overall Summary and Recommendations When sequences were divided into two groups (10 Based on the discussion above, overall findings are re- drivers made errors versus <10), seven fall into the first iterated and some recommendations made. category while five fall into the second. The curves where more drivers made errors already had more exten- sive treatments. This was especially true with the use of Advisory Speeds chevrons where four of the seven more problematic sequences had chevrons present versus only on one of Findings and recommendations regarding advisory speeds the other group (of five). Contrarily, neither of the two are as follows: worst curves had chevrons deployed. The two sequences on gravel roads showed opposite The DPM subjects routinely exceeded posted advisory results. For one sequence, there were very few errors as speeds. These findings are consistent with findings from drivers approached and drove through the curves conser-