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In previous studies, little attention has been paid to developing methods for estimating passenger car equivalent (PCE) factors under oversaturated conditions. This paper presents a new method to estimate PCE factors for heavy vehicles based on the assumption that backward wave velocities keep consistent under oversaturated conditions. As the variations of backward wave velocities in mixed flows will be minimal if the traffic stream is uniform, a minimum relative standard deviation optimising model is given based on backward wave velocity. The traffic data drawn from I-80 datasets provided by the next generation simulation are utilised to analyse this method and prove the assumption. In view of the limitation of empirical data, Vissim microscopic traffic software is used to simulate oversaturated traffic flow under different percentages of heavy vehicles. The results show that the effects of heavy vehicles under oversaturated conditions are greater than those under free-flow conditions and the proportion of heavy vehicles has a major impact on the PCE factors. [ABSTRACT FROM AUTHOR]

The Highways Agency's National Traffic Control Centre (NTCC) became fully operational in November 2003. The services provided by the control centre are key to satisfying the objectives of providing better information to travellers and ensuring more reliable journeys. This paper describes the policy context within which the control centre has been delivered; the means by which it collects data on conditions on England's motorway and all-purpose trunk road network; how those data are analysed; and the means by which information is disseminated to the general public. These services are providing the catalyst for the development of traffic information delivery tools by the Agency and private sector information providers. [ABSTRACT FROM AUTHOR]