In this work the results of an innovative approach aimed at defining an optimised traffic emissions calculation scheme are presented. The study started from the evidence that the inaccuracy of the classic `average speed approach' and the inherent difficulties of advanced approaches based on `instantaneous emission factors' do not offer - for opposite reasons - an adequate solution to the problem of assessing impacts of urban transport policies on traffic when the accuracy of emission models is a limiting factor. The proposed approach is based on a `correction' of emissions calculated from average speed with a `Congestion Correction Factor' (CCF) taking into account the infinite different ways an `average speed' can be experienced by vehicles along a link. Such a correction factor represents the speed variability along the link, and is derived as a function of variables easily available to the traffic engineers: link length, traffic density, link average speed and percent of green at traffic light. This innovative model is now included in the TEE (Traffic Emissions and Energy) model being developed at ENEA since 1992 and representing one of the most complete and sophisticated traffic emission models in Europe. (A)
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