The computer program for a completely revised version of the APRAC-1A diffusion model is presented and discussed. The new code uses EPA's emissions calculation methodology from Supplement No. 5 to AP-42. Gridded, and link by link emissions can be output for hydrocarbons, carbon monoxide or oxides of nitrogen. Diffusion calculations make use of a receptor-oriented Gaussian plume model. Local winds at the receptor can be used; they are interpolated from multiple wind inputs. Mixing heights may be calculated from sounding data, or input directly. Two local source models are available, one treating pollutant behavior in a street canyon, the other treats vehicle and pollutant effects at a signalized intersection. A small program is included for decoding Federal Highway Administration data tapes...Software Description: The program is written in the Fortran programming language for implementation on a DATA 100/78 computer. 300K bytes of core storage are required to operate the model.