AgdaPkt 2000-08-28 - Laserfiche WebLink

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/OA7 hump installation.' Before hump installation, approximately 550 vehicles per day drove on the subject section of Edgewood at speeds above 35 mph. After hump installation this total has been reduced to an average of 37 per day. This is obviously a significant benefit to the residents of Edgewood Road. The figure also shows that none of the surrounding streets are adversely impacted by having numbers of very high-speed drivers diverted to their streets. In fact, occurrence of speeds exceeding enforceable citation threshold on Blandford declined from an average of 12 per day to 8 per day, apparently the result of the stop signs that were installed there in concert with the hump program on Edgewood. Figure 5 provides a multi-stage sequence of eighty-fifth percentile speed measurements on Edgewood and on Blandford. The first measurements were taken in the winter of 1999 before any control actions had been taken. The second measurements were taken in June, 1999, in the immediate aftermath of a period of saturation speed enforcement by the Redwood City Police Department. The third measurements were taken in April/May, 2000, after the humps' and stop signs were in place. The figure shows that saturation enforcement did lower speed some, but not to the extent that residents desire, on Edgewood. Achieving the change required maintaining a level of police presence in a limited area that is beyond what is practical for the community to afford on a long term basis. The traffic control changes provided a more extensive and continuous speed reduction at a relatively limited one-time cost. The humps on Edgewood appear to have had what might be termed "spill-over" benefits. Before and after speed measurements were also taken on the block of Edgewood just west of Sommerset, a block outside the segment where the speed humps were employed. In this segment of Edgewood, the eighty-fifth percentile speed dropped from 32 mph to 31 mph, a modest but desirable change. Much more significant is the change in the number of vehicles per day exceeding 35 mph (120 per day before the humps, an average of 63 per day) since the humps have been in place. Effects On Noise FiGures 6 throuGh 8 present comparisons of limited acoustic data taken before and after hump installations. The data were taken at approximately the same time of day before and after humps were installed. Since most users of the street are "regulars", roughly the same vehicle/driver population was observed in the before and after measurements. Instantaneous sounds of vehicles passing the hump locations are shown on Figure 6. The noise of normal automobiles passing and the noise of vans, pickups and sport-utility vehicles was less, on the average, with the humps in place, than before the humps. Average continuous sound levels, shown on Figure 7, were less at the hump locations when the humps were in place than before the humps were installed. However, the difference is insufficient for the improvement to be perceptible to most individuals. In the limited acoustic data collected, the percent of vehicles on the street causing very loud sounds near the hump locations was slightly less with the humps in place than before the , The 35 mph threshold is considered significant both because residents are often most disturbed by the number of very fast cars rather than averages or eighty-fifth percentiles and because in enforcing speed citations courts commonly grant motorists about 10 mph leeway above the posted speed limit. Hence, 35 mph constitutes both a threshold of severe resident irritation and of enforceable speed violation. -4- '."r--'-'T"