Estimation of capacity and delay at work zones in urban areas.
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Civil works on engineering projects often require the Contractor to close off part of the road to allow uninterrupted construction and safety of own workers. However, in case where the road section is narrow, lane closures in the work zones often result in excessive delays and queuing of regular traffic. This results to loss in working hours, agitation and could result in safety risks to the Contractor. As such, it is important that lane closures minimize travel delay and queuing. There is however, limited knowledge on the general impact of lane closures on delay, capacity, and queuing in work zones in Uganda. The present study examined capacity and delay of work zones taking into account the length and width of available section shared by traffic in two directions, and the arrival demand upstream the work zone in two directions. The data used in the study was collected at five work zones located along Hoima road at: Kasubi, Nakulabye and Bakuli. Two work zones were located in Kasubi, one in Nakulabye and two more in Bakuli. The work zones were all 4-to-2 lane closures. The data was collected using manual counts methods for traffic volumes (arrival, queue lengths and work zone discharge), and video recording for delays per vehicles arriving in the work zone. The capacities of the work zones were taken as the maximum discharge volumes. The results show that the capacities of the five site work zones were 1474, 999, 1305, 1056 and 491 vph and the maximum delays were 444, 300, 767, 471 and 245 seconds. The 588 meter long work zone exhibited delays ranging from 498 to 767 seconds. The 169.5 meter work zone exhibited delays ranging from 179 to 444 seconds. The 81 meter work zone exhibited delays ranging from 9 to 245 seconds. It can be noted that longer work zones exhibited higher values of delay. These results show that in order to minimize delay in work zones, the section should not be longer than 300 meters, and when volumes exceed 1474 vph, it is important that more than one directional lane is provided to accommodate arrival volumes and minimize travel delays where possible.