Pollution caused by road traffic in cities is a major problem, and Computational Fluid DynamicsComputational Fluid Dynamics (CFD) (CFD) has become an established tool for its investigation. Wind tunnelWind tunnel and in-situ measurementsIn-situ measurements showed, that the moving cars themselves influence the flow patterns and pollution dispersion. Hence, these effects must be considered in the numerical procedure in certain situations. We present a system of additional source terms for the Reynolds Averaged Navier–Stokes equations (RANS) to model the effects of moving traffic. Comparison with wind tunnelWind tunnel measurementsWind tunnel measurements shows that this approach correctly reproduces the effects of traffic in a street canyon under perpendicular inflow. The method only requires the definition of additional fluid volumes along the streets and takes the direction of vehicle velocity into account. It can be easily transferred to roads in real urban environments and gives also for this case results that are in good agreement with measured results.