"July 1981." "EPA-909-9-81-002." "SRI Project 8855." "Contract 68-02-2548." "Prepared for U.S. Environmental Protection Agency."

Instructions on the use and applicability of the APRAC-3/MOBILE1 emissions and diffusion model are presented in this manual. The previous version of the model, APRAC-2, completely revised the methodology of the original model, APRAC-1A. The latest version of the model remains basically the same as APRAC-2 with the exception of two important modifications. First, the emission factor computation methodology has been revised to reflect the EPA's latest update, and the portion of the code that performs those computations has been separated from the model's emission rate and diffustion modules to facilitate incorporation of future emission factor methodology updates. The second modification to the model will increase computation efficiency by automatically treating traffic links in the primary network with low vehicle miles of travel (VMT) as area sources. This will allow the remaining primary link file to fit into core storage rather than incurring the numerous and expensive input/output operations necessary when the primary traffic file is large.