Abstract:
Motorway crashes are critical from a traffic safety as well as an operational point of view. They not only impact traffic safety but also cause non-recurrent congestion. The probability of a crash is significantly affected by the traffic flow and the environmental weather conditions that can change adversely. An analysis of road crash data and contributing factors with varying traffic flow are evaluated in this dissertation. A case study using data collected over an 11.28 km section of Auckland's Southern Motorway (State Highway 1) identified factors that includes time periods, weather, lighting conditions, weekday/weekend and others that were over representative. Volume to capacity (v/c) ratios, Level of Servive (LOS) and traffic regimes under which higher crash rates occurred are identified. 30sec loop detectors' data from the Sydney Coordinated Adaptive Traffic System (SCATS) and Crash data from the New Zealand Transport Agency (NZTA) Crash Analysis System (CAS) database over a one year period from 1st June 2009 to 31st May 2010 were obtained and analysed. The research demonstrated that the highest frequency of crashes occurred in the PM peak period when traffic flow was heavy between 3600 to 4788 vehicles per hour. The crash rates on this motorway section generally increase with increasing traffic volume to capacity (v/c) ratio conditions, up to a maximum of 27.8 crashes per 100 Million Vehicle Kilometres Travelled (MVKT) at 0.7 v/c ratio (corresponding to a Level of Service (LOS) of "D"). This crash rate is more than double the crash rate at 0.5 v/c ratio. This research also surprisingly shows that the crash rate then decreases from this maximum rate to 8 crashes per 100MVKT at capacity conditions (v/c ratio = 1.0) being approximately the same crash rate as a v/c ratio of 0.4. Most of the rear end (non-injury) crashes occur during day time peak hour periods. The findings of this research are relevant to the agencies and road safety engineers responsible for management, operations and safety of Auckland's Motorway Networks (although also relevant to some other parts of New Zealand and congested networks internationally) helping them in developing better methodologies for safe traffic operations and management on motorway networks. This post graduate research has been undertaken in conjunction with the Auckland Motorway Alliance (AMA).