[en] The three-dimensional diagnostic wind field model (MATHEW) and the particle-in-cell transport and diffusion model (ADPIC) are used by the Atmospheric Release Advisory Capability (ARAC) for real-time assessments of the consequences from accidental releases of radioactivity into the atmosphere. For the dispersion of hazardous heavier-than-air gases, a time-dependent, three-dimensional finite element model (FEM3) is used. These models have been evaluated extensively against a wide spectrum of field experiments involving the release of chemically inert tracers or heavier-than-air gases. The results reveal that the MATHEW/ADPIC models are capable of simulating the spatial and temporal distributions of tracer concentration to within a factor of 2 for 50% of the measured tracer concentrations for near surface releases in relatively flat terrain and within a factor of 2 for 20% of the comparisons for elevated releases in complex terrain. The FEM3 model produces quite satisfactory simulations of the spatial and temporal distributions of heavier-than-air gases, typically within a kilometer of the release point. The ARAC consists of a centralized computerized emergency response system that is capable of supporting up to 100 sites and providing real-time predictions of the consequence of transportation accidents that may occur anywhere. It utilizes pertinent accident information, local and regional meteorology, and terrain as input to the MATHEW/ADPIC models for the consequence analysis. It has responded to over 150 incidents and exercises over the past decade