Design Hourly Volume from Road Users' Perspective

The tradition of selecting the 30th highest hourly volume or what is known as the ``knee-of-curve'' approach for road design is based mainly on the facility utilization because it permits a given road facility to be congested for a certain number of hours during the year. This note reexamines the design hour volume concept from the users' perspective. Alberta's highway system is investigated and the users' perspective is considered by classifying the road sites into several types according to trip characteristics, such as trip purpose and trip length distribution. The main conclusions of the study are as follows: (1) the type of road use is a significant variable that should be considered for appropriate design hour volume; and (2) to provide a more uniform service to the users of various road facilities, it is better to use different highest volume hours for designing different types of roads.