Work zone and construction impacts on arterial streets can constitute a considerable source of congestion in North Carolina metropolitan areas. Work zones that cause a "significant" disruption to the traveling public are required to undergo a performance evaluation to assure that impacts can be minimized to the extent possible. This includes decisions on the types of work zone configurations to be considered, as well as an assessment of the feasible times of day during which construction activities are permitted. The analysis of the operational impacts of work zones is important to estimate travel time, delay, and user cost borne by motorists and the community due to construction activities. Therefore, finding the best ways to operate and control arterial work zones provides a safer condition for drivers and improves mobility. The increase in work zone activities motivates the development of a tool that can estimate the impact of work zones on urban arterial streets. For this reason, NCDOT sponsored research project RP-2013-09 titled "Delay and User Cost Estimation for Work Zones on Urban Arterials." This project is ongoing and has provided a new arterial work zone saturation headway model for signalized intersection.
However, saturation headway on signalized intersection alone does not support a full assessment of the operational impacts of work zone activities. It is also necessary to define the resulting ratio of effective green (g) to the cycle length (C). This ratio, known as the green ratio and denoted as g/C, is a key attribute of intersection capacity. The green ratio is used directly to predict lane group capacity in analytical analysis approaches such as the Highway Capacity Manual (HCM) methods. Furthermore, most of the signalized arterials maintained by NCDOT use semi-actuated coordination. Under semi-actuated coordinated control, the g/C ratio for the coordinated phases are not fixed but dynamically vary cycle by cycle as demand fluctuates. Therefore, there is a need to study urban arterial work zone capacity in a way that explicitly considers dynamic g/C ratio under various work zone configurations.
In addition, work zones on signalized arterials affect not only intersection capacity but also corridor travel speed. There is high possibility that arterial coordination will also be disrupted due to such progression speed changes. Therefore, an analysis tool is needed that includes models to predict the impact to coordinated phase green ratios and work zone travel speed in addition to modeling the impact to saturation flow rates.
This project seeks to develop methodologies for estimating the capacity reduction and progression degradation on arterial work zones in North Carolina due to the combined effect of saturation flow rate, green ratio, and arterial travel speed reductions. The research will be conducted using NC-specific empirical performance data gathered in active arterial work zones. NCDOT recently sponsored related projects RP-2012-12 and RP-2013-09. These projects provided arterial performance monitoring methods with signal coordination strategies as well as arterial work zone saturation headway models. The methodologies developed in this proposed project will be implemented in an enhanced version of the software tool (ARTVAL-WZ) developed under NCDOT RP-2013-09. The resulting arterial work zone analysis tool that will have a two-tiered level of analysis that allows initial planning level assessment by the Work Zone Traffic Control group with support from the Congestion Management group and, if necessary, detailed analysis by the Central Office Signal Timing (COST) section.
