Vehicle simulators are widely used to test the correctness of vehicle control algorithms. It is important to create a virtual road environment in a way that the vehicle algorithm can be tested under various circumstances that may happen in the real world. However, building such a road environment is typically time consuming and performed in a manual and ad-hoc fashion without having a good notion of coverage criteria. We propose the automatic road network generation for vehicle simulation that is based on Satisfiability Modulo Theories (SMT). We first introduce the curve coverage criteria to characterize the property of horizontal/vertical curves that are required to test advanced safety features such as adaptive cruise control or lane keeping assistance. This criteria includes the number of curves, the distance of adjacent curves and horizontal/vertical curvatures. We propose the road network generation algorithms that utilize the SMT solver to determine a set of 3 dimensional coordinates. This algorithm takes an input of the parametrized constraints formalized from the curve coverage criteria and automatically determines a set of 3D coordinates to generate the road structure. Vehicle simulation engines can then use these coordinates to visualize the road networks, and such road networks are guaranteed to conform to the curve coverage criteria. We developed a plug-in for the Unity3D simulation engine that automates this process and demonstrate the applicability of the generated the road network for the adaptive cruise control testing.