Calibration of a Congestion Load Model for Highway Bridges Using Traffic Microsimulation

For short- to medium-length bridges, the governing traffic loading scenario may be that of congested traffic. This paper presents the calibration of a congested traffic load model using traffic microsimulation. A range of bridge lengths, forms of construction, and load effects is considered. Different driving parameters and traffic composition are also considered. The influence of these parameters on the resulting load effect is determined. For each of these scenarios, a calibrated gap between trucks is determined to replicate the traffic microsimulation results. This calibrated gap can then be used as part of a simpler congestion model, suitable for bridge assessment. Such simpler models can be used to simulate much longer periods than are possible using traffic microsimulation. It is found that the calibrated gaps are either similar to, or are larger than, previous work in the area. Consequently, this approach helps to remove some conservatism from congested traffic load effect estimation, and this may find valuable application in the assessment of existing bridge structures.