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8 · Seeing the curve in advance, especially through the addi- provided in three separate categories: where there were no or tion of reflective visual aids for nighttime driving such slight differences among the respondent groups, where there as chevrons or by clearing obstruction near TCDs. were differences by state, and where there were differences by crash versus typical drivers. Participants indicated that they tended to drive slower and The first set of summary statements contains those where closer to the posted advisory speed when driving unfamiliar there were no substantial differences among the groups of curves. When driving familiar curves, participants indicated respondents: that they routinely go at least 5 mph over the advisory and/or about 5 mph faster than they would at an unfamiliar curve (the · Except of the local Michigan crash group, respondents responses were not necessarily consistent). In general, speed were generally confident that they knew the difference advisories were perceived as a warning to "slow down" but between advisory and regulatory signs. not necessarily to the advisory level. In that context, there was · Respondents generally stated that advance curve warning considerable variance in how speed advisories should be used signs helped them anticipate and drive through a curve. and at what level they should be set. However, the participants · Respondents generally stated that large arrows and indicated that they felt that changing advisory speeds at rural chevrons as well as pavement markings helped them curves is not a high priority for change or use of financial anticipate and drive through a curve. resources. Most of the participants have their own method of · The most prevalent comment about advisory speeds was relating their speed to the posted advisory speed. that their use "depends" on one or more factors such as weather and visibility. Many respondents commented CRASH-INVOLVED AND TYPICAL/ that they generally interpreted the advisory speed as a AVERAGE DRIVER SURVEY message to "slow down," even if not to the actual speed noted on the advisory sign. Few respondents reported As noted, both a focus-group exercise and a survey were actually driving at the advisory speed; conversely, numer- undertaken to assess driver responses to different curve- ous comments were made to the effect that advisory related issues. The focus of the survey was also on rural two- speeds are routinely exceeded. lane, two-way roads. The topics were parallel to both those of · There was no consensus on how appropriate advisory the driver focus group and the practitioner-related exercises speeds should be determined: fully 25% thought it should and included the adequacy of existing signs; perception of and be the maximum safe speed, more than 30% thought it response to specific TCDs, identification of what makes some should be faster than most drove, and 36% thought it curves more difficult than others, the extent to which famil- should be a "comfortable" speed on dry pavement. iarity is a factor in difficulty with curves, what types of roads · While speed was often mentioned in the context of prob- present the most difficulty, how TCDs for curves could be lems with curves, 42% of all the respondents indicated improved, characteristics of their own "worst" curve-related that their worst-curve experiences occurred on roads experience, and whether that "worst" experience on a curve with speed limits of 50 mph or less. had short- or long-term effects on driving habits. The drivers · The "top five" characteristics of problem curves include were broken into two basic groups: drivers involved in a motor- very sharp, no advance signs, over top of a hill, getting vehicle crash on a horizontal curve within approximately two sharper as the curve is traversed, and unexpected. With years; and typical or "average" drivers. The survey was done minor variations, these were listed by all groups. Violation in both Michigan and North Carolina. There were actually of driver expectation appears to be the common thread. seven different driver groups queried: typical Michigan-local, · The "top three" sign-related solutions were to lengthen typical Michigan-statewide, typical North Carolina, two the distance between the advance signs and the curves, sub-groups of crash-involved Michigan-local, crash-involved to increase sign size, and to increase the number of Michigan-statewide, and crash-involved North Carolina. The advance signs. All of these are concerned with giving differentiation between local and statewide Michigan drivers the driver the appropriate information earlier and appear occurred because there was interest in identifying a "local" to be consistent with the "top five" problems. crash group for other phases of the project. The local group · In the context of fixing problem curves, while TCD was composed of drivers in and around the greater Lansing changes were often mentioned as remedies, other fac- area, which included both the urbanized Lansing/East Lansing tors such as geometric changes were mentioned more area as well as the surrounding six counties that are largely often. This is in spite of the clear emphasis in the survey rural agricultural areas outside the immediate urbanized area. instrument on TCDs. The Michigan statewide sample was from the Lower Peninsula · If a curve "check list" was to be made on how to "fix" only. The overall response rate was 13%. curves, it would include correct the superelevation; install/ The following summary and discussion are based on stated maintain good-quality center- and edgelines; ensure that preferences and do not necessarily represent how respon- appropriate advance warning signs are present; generally dents actually perform on the road system. The summary is make sure that the road, shoulders, and right-of-way are
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9 well-maintained; and provide special emphasis on "bad" · Typical respondents were more likely to think that or dangerous curves. curves "far away" from home were the most problematic while crash respondents indicated that "closer" curves In some instances, there were variations in answers to ques- were--that is, it is likely that those who crash on curves tions that could be attributed to the respondent's state of resi- do so more often on roads with which they are familiar. dence. While these are highlighted below, it is not clear that the This is in spite of an earlier assertion that familiarity with variation is really state- or region-related. In many instances, curves was a significant issue for all groups. the variations among the various groups in Michigan were more · While all respondents cited poor weather or pavement pronounced than those between the two states. Although the conditions, poor visibility, darkness, and unexpected majority of all respondents indicated that they used advisory traffic as important contributors to curve problems, the speeds as "guides," Michigan respondents were more likely crash groups cited poor weather more often. Conversely, to use them in that manner and less likely to say that they darkness was more often cited by typical drivers. drove at the advisory speed. It is not clear why this difference · While all groups cited speed-related problems when de- exists--it may be a function of the perception of speed-limit scribing their "worst curve" experience, the crash groups enforcement in general. were less likely than their counterparts to cite "going too The variations in answers that could be attributed to re- fast" as part of the problem. Ironically, most groups spondents' state of residency are as follows: thought that advisory speeds are too low while citing going "too fast" as a contributing factor in worst-curve · While all respondents thought familiarity was a signifi- experiences. cant issue in successfully negotiating curves, it was rated · Crash groups were somewhat more desirous of change as more important by Michigan respondents. in signs and markings. Overall, approximately 25% of · Michigan respondents were more likely to report gravel the respondents did not think any TCD-related change roads as a contributing factor in making curves haz- was necessary. ardous. This may simply be a function of there being · Crash groups were somewhat more likely to think that more gravel roads in rural Michigan. bad curve experiences had an effect on driving behavior · The North Carolina respondents were more likely to cite although all groups stated that, not surprisingly, the a combination of factors in describing their worst curve effects lessened over time. experiences. Overall, while there were some differences in responses Finally, there were differences between respondents who by state, it is not clear that the differences are related to had been involved in a curve-related crash and the "typical" intrinsic regional behavior differences or simply differences respondents. While some crash respondents may not have in the roadway system such as fewer gravel roads in North been involved in crashes on curves because of difficulties in Carolina. On the other hand, there were often clear differ- locating actual crash locations, they had certainly been in- ences between crash and typical respondents. Drivers who volved in some crash; likewise, while some of the typical, had been involved in crashes were more likely to state that their randomly selected respondents may have been involved in worst experiences occurred closer to home than were the typ- crashes, it should be much less likely. These caveats notwith- ical respondents, and they were more likely to indicate the standing, differences between the two groups included the need for more or better communication. While the former following: confirms what is known about many crashes occurring closer to home, it is not clear what the implications are for TCDs. · Crash groups in both states were more likely than their Improved communication would probably not help drivers in typical counterparts to disagree with a statement indi- many of their familiar problem situations. On the other hand, cating that they were getting enough advance informa- all respondent groups stated that "fixes" that deal with geom- tion about upcoming curves. etry and other design features are more important than mod- · Although all respondents were generally positive about ifications of TCDs. In regard to changes needed for TCDs, advisory speed signs, crash groups were more likely to for the most part, respondents seemed satisfied with the ones disagree with a statement indicating that advisory speed they routinely encounter. However, they were adamant in sug- signs were helpful. gesting that center- and edgelines be more widely used. Inter- · While crash-involved respondents were not overwhelm- estingly, there were very few comments about the use of ingly honest in reporting their "worst curve" experience, chevrons, large arrows, or both. they were far more likely to note involvement in a crash There is cause for concern with respect to speed advisory than were typical groups. signs. While most respondents report using the advisories as · Typical respondents were more likely to think that curves a general guide and as a suggestion to "slow down," they also on gravel roads were a more serious problem than did the indicate that they typically exceed advisory speeds. At the crash respondents. same time, they often cite excessive speed as a reason for