Sound impact of road and railway infrastructures are more and more severely regulated by European laws: acceptable thresholds in emission and reception are decreasing. This implies to develop propagation models able to take many phenomena into account at the same time (meteorology, uneven ground, impedances discontinuities...). The parabolic equation (PE) is one of those numerical methods. Its main purpose is to predict long-range sound propagation under range-dependant environment. Despite of its efficiency, this method shows a number of limitations in complex outdoor situations. This paper aims at presenting ATMOS (Advanced Theorical Models for Outdoor Sound propagation). This GFPE (Green’s Function Parabolic Equation method) based calculation code is dedicated to complex outdoor situations which can not be solve with a classical PE approach. Usually PE neglects backscattering and complex topography can not be considered. ATMOS takes those phenomena into account by new several techniques: complementary Kirchhoff approximation, GFPE-BEM hybrid method, referential rotation. The atmosphere properties are included into the range dependant sound speed profile, integrating atmospheric attenuation, density fluctuation, wind, temperature gradients and turbulence… All those parameters may be varying with height and distance along the propagation. Numerical examples of road traffic configurations that illustrate those combined effects are presented and compared to scale model measurements.