Evaluating Reliability, Resiliency and Vulnerability of Urban Expressway

Abstract

The trend of increasing transportation demand with limited road network needs an exploration of evaluating performance of a transportation system. A transport network is a place where various interactive situations occur that arise complexity in a system. In such a system, urban expressways play an important role by reducing some of the variability associated with travel time by directly connecting major attraction and production zones. However, they are expensive and thus, limited in number and with sparse space to accommodate a high proportion of transport vehicles, some questions may arise that how often an urban expressway may fail, how quickly it recovers from the unstable states and how severe the consequences of failure of that system may be. Although there have been some research on estimating the vulnerability of transportation networks, the effort to evaluate the reliability, resilience and vulnerability (R-R-V) of an urban expressway in isolation has not been explored. This study presents an analogy between urban expressways and water stream and applies the popular methods used in water resource engineering to evaluate the R-R-V of urban expressways. For this, it selects Shibuya 3 route of Tokyo Metropolitan Expressways Company Limited as study area, which is heavily instrumented with detectors with an almost uniform spacing of 250 meters. . Six month data on traffic flow variables, e.g., speed, flow and occupancy for every minute for every detector location, along with road crash data were collected. R-R-V were calculated by comparing the quality of traffic stream density with the jam density of the respective location where any density below jam density was identified as satisfactory operational condition. R-R-V provides one of the most comprehensive approaches for analysing the probability of success or failure of a system, the rate of recovery of a system and to quantify the expected consequence of being in unsatisfactory states. The result from reliability heat map, resiliency and vulnerability curve advocates that there is high sensitivity (chances of system failure) in on-ramp, off-ramp zones of the route network. Due to congestion and crashes, system recovery rate is very much lower in connectors as it hampers traffic flow in both ways. These findings can be valuable in the evaluation and selection of alternative design and operating policies for a wide variety of transportation system performance with a variety of operating policies.