Truck Level of Service: Conceptual Methodological Exploration

Although the passenger car is the most dominant mode of transportation on the roadway system, commercial trucks are also a very important mode because freight movement is vital to the Nation’s economy. The efficient movement of freight is becoming an increasingly significant issue to all levels of government. Consequently, the ability to accurately measure operational parameters and corresponding levels of service for large trucks is becoming increasingly important. This would also allow for the ability to more effectively evaluate such policy issues as truck lane restrictions and dedicated truck lanes, which continue to get increased attention. The current LOS methodologies prescribed by the Highway Capacity Manual (HCM) for various roadway facilities present single LOS criteria for all vehicles that use the facility. While passenger cars, buses, recreational vehicles, and heavy trucks all use these facilities, the LOS values determined by HCM procedures apply to the traffic stream as a whole. With this method of determining level of service, trucks and passenger cars cannot be examined separately. This paper presents an exploratory investigation, and development, of a methodology for assessing the level of service for heavy trucks in the traffic stream separately from that for passenger vehicles, for basic freeway segments. This methodology is based on a ‘relative maneuverability’ concept, which is a function of the ratio of percentage of free-flow speed of trucks to percentage of free-flow speed of passenger cars. Speed prediction equations were developed (via microscopic simulation, a factorial design and regression analysis) for various classes of trucks, as well as for the passenger car, for use in calculating a ‘Relative Maneuverability Index’, which is subsequently used to determine truck level of service.