Loading on long span bridges in heavily trafficked areas

The critical traffic loading condition for long-span bridges is congestion when vehicles may be closely spaced together. Data on very high traffic flows is limited however, as induction loops which are typically used to collect traffic data, are ineffective when traffic flow breaks down. A number of long span bridges are located in areas of high traffic with periods of recurring congestion occurring daily. While the inter-vehicle gap distances are greater than those occurring during non-recurring full stop accident type events, the high frequency of the recurring congestion events can increase the probability of a critical load case occurring. A location on the N7/M7 national primary route in Ireland is identified where regular congestion occurred due to a lane drop. Traffic monitoring using an Unmanned Aerial Vehicle (UAV) is carried out, generating a significant amount of high quality footage of congested traffic from a bird’s eye view. A method of processing the data is developed to transform the trajectory data into a traffic stream that can be used to simulate load effects on long span structures. The process is applied to 2 notional long span structures. Insights into the load patterns that give rise to critical loading events are identified for both structures