DETERMINING THE SPEED-FLOW RELATIONSHIP AND CAPACITY FOR A FREEWAY WORK ZONE WITH NO LANE CLOSURE

摘要

Speed-flow relationship in work zones has been a rather infrequent research topic. This studyexamines the speed-flow relationship of a selected work zone with no lane closure. A step-by-stepprocedure is presented to develop the work zone speed-flow curve as a three-regime model that involvedfree flow, transition, and congestion regimes, respectively. Field data showed that the free flow regimeexisted up to a flow rate of about 800 passenger cars per hour per lane (pcphpl), which is much lower thanthat of the Highway Capacity Manual (HCM) 2000 models for basic freeway sections. In the transitionregime, the average speeds were observed to decrease at a rate higher compared to the HCM 2000 modelsfor basic freeway sections. The congestion regime of the speed-flow curve was constructed in the form ofa power function. Using this three-regime speed-flow curve, the work zone capacity was estimated to be1900 pcphpl, which checked very well with the maximum 15-minute flow rate of 1891 pcphpl estimatedfrom the work zone headway data.By using the step-by-step procedure used in this study, work zone speed-flow relationships can bebetter understood and work zone capacity can be accurately estimated. Accurate estimation of work zonecapacity leads to more efficient operation in a real-time system, more appropriate information on travelpattern, more accurate diversion and traveler information for alternate routing, and improved reliability ofthe transportation system.