C.C. Caprani & E.J. OBrien THE GOVERNING FORM OF TRAFFIC FOR HIGHWAY BRIDGE LOADING

Traffic loading is one of the most variable parameters in a bridge reliability assessment. Its accurate assessment potentially offers large savings due to reduced bridge rehabilitation or replacement costs. It is frequently assumed that free-flowing traffic (incorporating dynamic effects) governs for short- to medium-length bridges, whilst congestion governs for longer bridges. In this paper, for a range of bridge lengths and load effects, several traffic congestion models are considered, including the most common in the literature, as well as a model based upon traffic micro-simulation. For the critical model, the dynamic ratio that would be required for free-flowing traffic to govern is determined. For a range of bridge lengths, these dynamic ratios are larger than would be expected, and thus the authors conclude that contrary to the common assumption, the governing form of traffic may be congested traffic