Dedicated Short Range Communication (DSRC) standards have been defined as the physical and MAC layers in the context of vehicular communications. In this work the performance of DSRC communications are analyzed in the context of roadside to vehicle environments for different traffic loads. Based on these results optimal configurations are proposed for the physical parameters of the roadside beacon: output power transmission, and antenna height and tilt, as well as for the length of the packets and the access mechanism. An accurate physical model was used, with actual antenna patterns intended for the 5.9GHz band, suitable propagation models, and assuming capture effect in the packet error computation. Results show notable divergences among roadside configurations for different traffic loads and optimization criteria. Indeed, simulations have shown that a vast majority of errors come from simultaneous transmissions, suggesting the use of suitable link layer protocols.