Urban freeway has played a key role in the transportation system in a big city. However, it has experienced a transportation problem due to the increased traffic exceeding the capacity since 1980's. Additionally the transportation systems management(TSM) and intelligent transportation systems(ITS) have been introduced for solving the transportation problem with the transportation facility construction and extension limited since 1990's. Despite all these efforts, urban freeway is experiencing the social and economic losses from a severe traffic congestion. Thus, urban freeway traffic management system(UFTMS) should be systematically devised for promoting the efficiency of urban freeway.
First of all, it is important to perceive and demarcate the characteristics on the operational conditions of urban freeway for constructing the UFTMS. There are the levels of service(LOS) to describe the operational conditions within traffic flow, based on the service measures such as freedom to maneuver, traffic interruptions, and comfort. However, LOS F has not kept up with the changes in the travel patterns for the past 20 years. It did not distinguish the increased levels of congestion nor did it help to prioritize the facility improvement, mitigation or transportation solutions for the increased congestion magnitude. Thus, it is necessary to additionally add the levels of service(LOS) within the LOS system.
The purpose of this study is to expand the levels of system under LOS F and advance the reporting system by distinguishing between varying degrees of failure on uninterrupted transportation facilities, especially on merge areas of urban freeway. First, the traffic characteristics were identified on merge points of the 1st urban freeway in Busan, based on the principles of traffic flow theories and the existing literatures. Second, trafficability efficiency() during a traffic congestion was introduced as the measure of effectiveness(MOE) of the LOS system for quantifying a congestion with the concept of efficiency. Also, LOS F through J was separately conferred on the domain corresponding to each trafficability efficiency domain under the congestion condition. Third, the 15-min period-based multi-period reporting system was introduced to simultaneously report the worseness and duration of congestion. Finally, the congestion index(CI) and level(CL) were suggested to replace the lengthy alphanumerics by a simple integrated grade for the flexible periods.
From the LOS system expansion and the newly reporting system on the merge points of urban freeway, the following conclusions were drawn:
ⅰ) Congestion were not classified definitely into the density of influence areas, exclusive flow rates or average travel speed on the merge points of urban freeway.
ⅱ) Trafficability efficiency(), introduced with the concept of efficiency on roadway facilities under congestion, showed the better MOE's on ramp junctions of urban freeway because the boundaries of each level were divided clearly into quantification of congestion.
ⅲ) Based on the relationship of flow rate and speed, it was suitable for expanding the LOS system under congestion to divide capacity and its critical speed into the five domains, respectively and to assign each domain of trafficability efficiency to LOS F through J.
ⅳ) The information of the duration as well as the worseness of congestion should be included as the level of service for congestion was reported, especially for grasping the real traffic flow characteristics every 15-min unit.
ⅴ) Integrated level of service(LOS) system, which was constructed with congestion index(CI) weighted for expanded level of service depending on the unit period and congestion level(CL) multiplied by the number of unit periods lasted, was expressed as the simple letter-typed level of service(LOS) for any congested period.
ⅵ) Congestion level(CL) was applicable to a selection of relatively inefficient areas and a criterion of prioritization for facilities improvement or traffic management.