Critical Transport Infrastructure in Urban Areas: Impacts of Traffic Incidents Assessed Using Accessibility-Based Network Vulnerability Analysis

Incidents (vehicle breakdowns, crashes, roadworks, lane blockages, severe weather, etc.) are believed responsible for about 50 percent of traffic congestion in Australia's major cities, which is a similar situation to that found in cities in many other parts of the developed world. Incident-based congestion is particularly disruptive because of its random occurrence in space and time, which maximises the operational impacts of the congestion on social and economic activities. This paper discusses a method for assessing critical locations-congestion hot spots-in urban road networks, and the development and application of diagnostic tools that will allow urban road system managers to anticipate potential vulnerabilities to incident-related congestion and take proactive action to avoid congestion rather than react to it. The expected Outcomes are then reduced congestion, delays, and pollution; significantly improved performance from the existing urban road system; and reduced pressure to build more roads. The method involves modelling of travel demand, network topology, capacity and road geometry, the identification and assessment of impacts of traffic incidents at specific locations in a road network, and the use of accessibility impact analysis to assess system-wide effects. Accessibility impact analysis is undertaken using an accessibility framework, which can account for time of day, transport mode and destination choices by individuals, and level of traffic congestion among other factors. A case-study application to a specific (potential) incident in a real-world network indicates that the proposed method is feasible and demonstrates its power in identifying not just total impacts but the distribution of those impacts across a region or community. While Current approaches to urban road network planning and management tend to be reactive-finding cures for problems as they arise or addressing locations of recurrent congestion or bad incident record-the vulnerability analysis method described in the paper should lend itself to a proactive approach that can anticipate structural weaknesses and vulnerabilities and help to avoid or at least temper potential adverse effects, rather than to react to them afterwards.