دانلود رایگان مقاله انگلیسی بازسازی زیرساخت بحرانی: براورد ریسک مبتنی بر منطق فازی - نشریه الزویر

Abstract

This paper presents a comprehensive framework for risk assessment and micro simulation modelling to assess traffic impacts during re-decking of a major suspension bridge identified as Critical Infrastructure (CI) in Halifax, Canada. The bridge is being replaced while maintaining traffic during day time. As re-decking is relatively a rare and unknown construction event for a Cable Bridge, unexpected risk event and uncertainty would be associated with complex engineering manoeuvring during the re-decking of the bridge. Therefore, this study proposes a fuzzy logic approach to estimate the construction related bridge opening delay, and subsequently develops a micro simulation-based traffic network model to assess the traffic impacts on transport network. Weather data, traffic volume and signal data obtained from multiple data sources have been used during the risk assessment and micro simulation modelling. The results suggest that the likelihood of bridge opening delay could range from 18%-30% for an hour period to 40% for 3 hour period depending on the level of consequence on any day in December. The average potential delay is obtained as 22 minutes, 1.5 hours, and 2.6 hours for low consequence, medium consequence, and high consequence respectively. Based on the delay analysis, this study evaluates three alternative bridge opening delay scenarios. It is observed that the increment in number of operating vehicles becomes steady at 30% suggesting the network has reached its capacity. The results also reveals that any delay over 2 hours in bridge opening would add a slight change to the impacts on the network. This study will help policy-makers to develop risk mitigation plans and contingencies to ensure better management of traffic during 18 months long re-decking of this critical infrastructure.

5. Conclusion and future development

This study presented a framework for fuzzy logic-based risk assessment and micro simulation-based traffic modelling for assessing the traffic impacts due to construction related bridge opening delay in the morning peak period. This study contributes to the gap existing in literature by assessing the traffic impacts of sudden delay in redecking of a critical infrastructure. Initially, the risk assessment estimated the probabilities of bridge opening delays depending on the level of consequences (i.e. low, medium, and high). For example, 1 hour delay probability in bridge opening is 18% and 30% with respect to cases- low consequence, and medium consequence respectively. On the other hand, 2 and 2.5 hour delay in re-opening the bridge is equally probable (40%) in the case of high consequence. The delay risk results then inform the scenario building process for traffic impact assessment within a microsimulation platform. The scenarios include (i) 1 hour delay (ii) 2 hour delay, and (iii) 3 hour delay in re-opening the bridge.

Next, each delay scenario is simulated for traffic impact assessment and compared to base case scenario (no delayed opening). The simulation results yield considerable traffic impacts on link level as well as on network level. The Mackay Bridge, as a major alternative link, anticipates a high re-routed traffic volume during the closure of the Macdonald Bridge. Results in Table 13 reveal that only 31% re-routed vehicle could cross the Mackay Bridge in the hour, 6:30 am -7:30 am due to a high base peak hour traffic volume on the bridge. As a result, queue grows rapidly and network gets saturated. This study found all the intersections saturated in terms of queue length for the whole evaluation period in the case of a 3 hour closure of the Macdonald Bridge. Moreover, average travel time increases by 33% and 45% in the case of scenario 2 (2 hour delay) and scenario 3 (3 hour delay) respectively with respect to the base case scenario (no delayed opening). From the operational point of view, the increment in number of operating vehicles became steady at 30% with respect to scenario 2 (2 hour delay) and scenario 3 (3 hour delay), which means the system has exceeded the capacity and any further delay over 2 hours in bridge operation would slightly change the impacts on surrounding network. Therefore, the congestion level that is found in terms of the changes in MOEs implies that the congestion reaches its threshold level in the absence of any warning of the closure incident.