IMPLICATIONS OF REDUCING THE TARGET HEIGHT USED TO DELINEATE PASSING ZONES

The current standard for establishing thresholds of passing zones on two-lane roads is based on target heights of 115 cm. As the percentage of Canadian vehicles equipped with daytime tuning lights continues to increase, it may become appropriate to lower the target height to 60 cm to correspond with the minimum height standard for headlights. The revision would recognize a possible change in behavior where the driver may become accustomed to identifying oncoming vehicles by the presence of headlights. With such a revision there will be a corresponding reduction in the number of passing opportunities on two-lane roads resulting in decreased operation levels. The net reduction will depend on prevailing terrain (level, rolling, mountainous) and operating speeds. A sample of arterial and collector highways was surveyed using a decreased target height of 60 cm to quantify the changes in passing opportunities which may result from a decreased target height. Results showed that a target height reduction would decrease the capacity utilization on facilities by an overall average of only 1% and in most cases there was no change in the level of service grade assigned to a facility.