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15 vatively, negotiating them with ease. The other sequence The drivers were observed to operate their vehicles "mechan- was more problematic with a much more abrupt curve ically" in an incremental rather than continuous process and with lower visibility through it. The conclusion, albeit did not respond to TCDs as if they were messages about what based on only two sequences, is that drivers will gener- was on the road ahead. The immediate responses were often ally "take it easy" on gravel roads and will perform well "tokens" of response--for example, drivers would take their unless a curve is more difficult or unexpected. This gives foot off the pedal although they would not actively slow credence to the idea that gravel roads may require less down, in spite of a speed advisory being present. While in signing except for "difficult" curves such as those where some instances this response was "good enough," in others it a turn arrow would be used when they should be signed was not. This is borne out by the quantifiable responses at sev- more aggressively. eral of the curves. If the curve was reasonably gentle and did not violate basic expectations, the drivers were in good shape. If the curve was a more serious undertaking, token responses Curves and Intersections then led to driver errors. The types of curves or situations where more drivers had errors included the following: Findings and recommendations regarding curves and inter- sections are as follows: Curves where the drivers had limited or no visibility of the curves when the TCDs were first visible; Notwithstanding the fact that all intersections were marked Curves where there were vertical curves, primarily hill with Intersection Ahead signs, intersections in the curve crests that obscured the curve; and caused difficulties for drivers. None of the signs "com- When the curve was combined with another element, bined" the curve and intersection warning. It is not clear especially intersections. what more could or should be done, but it is clear that the combination is indeed problematic and should be In general, although the curves were well-marked, the signed whenever it occurs--that is, drivers should always nominal responses to the TCDs (such as easing up on the gas be told when there is an intersection on or near a curve. pedal) were simply not enough when the situations were more complex. Consequently, a more positive or assertive Anecdotal Observations Based response was delayed until the drivers actually saw the extent on DPM Subject Performance of the curve or other feature. In some instances, modest responses caused later driver errors. There was also a general In addition to the more quantified results just recapitulated, "dilution" of the driver's attention--that is, in addition to a summary of more qualitative comments has also been pre- tending to the driving task, they also looked at the scenery, pared. The point of this exercise was to use the perspective asked general questions, talked on a cell-phone, or asked spe- of the DPM observer in assessing how drivers responded to cific questions. This performance can be compared with the curve-related TCDs and to the physical situations that they three trained MSP officers--they were highly focused on the encountered in the field. task at hand and not easily distracted.