Queue and user's costs in highway work zones

The IDOT Bureau of Design and Environment (BDE) Manual requires that traffic control plans for freeway reconstruction projects include a queuing analysis to determine the anticipated traffic backups in work zones. Queue length and delay calculations rely on the estimation of capacity and operating speed. In this study, field data were collected from five work zones in Illinois. Thirteen data sets were extracted from the field data. Each data set represents a particular traffic condition at a given site. A work zone capacity value was suggested for each traffic condition based on the field data. The suggested capacity for the sites with speed limit of 45 mph ranges from 1200 pcphpl (passenger cars per hour per lane) to 1550 pcphpl. The 1200 value was suggested for a traffic condition with flagger and queue, and 1550 value was for a traffic condition with no work activity, no speed management treatment and no queue. A capacity of 1600 pcphpl was suggested for a site with speed limit of 55 mph, dynamic speed feedback sign, no work activity, and no queue; and a capacity value of 1750 pcphplwas recommended for a short-distance work zone with speed limit of 55 mph, no work activity, and no queue. Using the field data, speed-flow curves were proposed for: work zones with speed limit of 45 mph and a flagger, work zones with speed limit of 45 mph and without a flagger, and work zones with speed limit of 55 mph. Each of these models can be adjusted to non-ideal conditions. Methods to estimate the length of moving queue, delay and users’ cost were developed to handle the cases where a demand higher than capacity causes queue. The queue length and delay were estimated for all the data sets using the proposed method. The results also were compared with the QuickZone 2 outputs. When the arrival volume in an interval was less than the capacity of the interval, the QuickZone2 did not yield any delay or queue length even though there was congestion and delay in a part of the interval.