Threshold 21 (T21) the simulation model presented in this paper aims to decision-makers and the public to better visualize, analyze, and understand the broader and longer-term implications of the varying underlying assumptions, policies, and strategies, including both their positive and negative impacts — both direct and indirect — and how to manage them. The T21-USA model results indicate that a continuation of current policies and trends will lead the US to become increasingly dependent on foreign energy resources and more vulnerable to price fluctuations. Furthermore, alternative scenarios simulating improved CAFE and Renewable Portfolio Standards (RPS) show that major reductions in the US' resource consumption and pollution generation could be possible while stimulating the economy over the medium and longer term. Nevertheless, the model shows that unintended consequences, such as the Jevons Paradox, have to be taken into consideration when defining national energy policies.