This thesis presents the research using finite element (FE) modeling and simulations to evaluate the performance of single-faced and double-faced W-beam guardrails for different heights under MASH Test Level 3 (TL-3) impact conditions. The modeling and simulation work was conducted on single-faced and double-faced W-beam guardrails with 29- and 31-inch rail heights and impacted by a 1996 Dodge Neon and a 2006 Ford F250. For the double-faced W-beam guardrail, the modeling and simulation work also included one with a lowered backside rail. Both single- and double-faced guardrails were evaluated under impacts of both vehicles at an impact speed of 62 mph (100 km/h) and a 25° angle. The simulation results showed the effects of guardrail heights on the vehicle's post-impact responses such as redirection, snagging, and spin-out. The use of FE simulations was shown to be both effective and efficient because of their inexpensive repeatability and adaptability. Furthermore, the FE simulations were extremely economical compared to conducting physical crash tests and thus recommended for future investigations of other roadside safety research issues.