The aerodynamic performance of road vehicles is quantified conventionally via an isolated-vehicle assumptions, while recent research has shown that aerodynamic forces and moments can vary by +/-50% in traffic, associated with proximity to vehicles adjacent lanes. Mapping the aerodynamic performance for common traffic scenarios requires hours of wind tunnel testing or time-consuming road measurements, however these interactions are caused predominantly by pressure field interactions and blockage effects, which can be replicated reasonably well using low-order CFD modelling. This paper examines various levels of simplification using a commercial CFD solver. Wind-tunnel data are used for validation, to demonstrate the ability of coarse-grid RANS, and simpler methods, to replicate the incremental changes associated with these on-road interactions.