NEGATIVE EFFECTS OF MID-BLOCK SPEED CONTROL DEVICES AND THEIR IMPORTANCE IN THE OVERALL IMPACT OF TRAFFIC CALMING ON THE ENVIRONMENT

The purpose of this study is to investigate previously unknown effects of speed control devices on fundamental characteristics of traffic, s uch as vehicle headway distribution, absorption capacity and average d elays to vehicles entering from driveways and pedestrian crossing oppo rtunity. Headway data were collected at seven sites in the Sydney Metr opolitan Area, under various levels of traffic flow and at various dis tances from the devices. The results demonstrate that although speed c ontrol devices do have some negative side-effects which are sometimes statistically significant, the magnitudes of the increase in average d elays and the decrease in absorption capacities around the devices are below the level that would conceivably influence the practical crossi ng and merging abilities. These minor inconveniences to pedestrians an d drivers are confined to the immediate vicinity of the devices and ar e, by far, outweighed by the benefits in terms of accident savings ove r the whole length of the street. (C) 1998 Elsevier Science Ltd. All r ights reserved.