Estimating the impact of abnormal loads on network performance

The English Highways Agency is required to improve network performance including journey time reliability measured by average delay on the 10% slowest journeys along a specified set of primary routes in the strategic road network. Abnormal indivisible loads, which behave as moving bottlenecks, can cause significant delay, but the factors involved are complex, so methods have been developed to model their effect. These methods have been extended to estimate their impact through the Average Vehicle Delay (formerly PSA1 delay) measure, allowing mitigations through intelligent transportation system or policy options to be evaluated. Environmental impacts are also considered.