To achieve the goal of universal coverage of health insurance for the Americans, in March 2010, the Patient Protection and Affordable Care Act (ACA) was signed into law. The ACA targets at providing help to improve access to affordable health coverage for everyone and protect consumers from abusive insurance company practices. One of the precedent mandates, implemented in September 2010, is to expand coverage on young adults of age 19 to 26, who may lose insurance coverage due to the remove from their parents’ plan after age 18 and lacking of productivity to bargain with employers in the labor market.

This dissertation looks into the impact of the ACA health insurance coverage expansion for young adults on the subsequent health outcomes, health care utilization, and further social impact on traffic fatalities. Difference-in-differences models are used with different treatment groups and corresponding control groups. Chapter I uses survey data (BRFSS) to evaluate health care access, health behavior and self-assessed health status. The results suggest an improvement in health care access and self-assessed health but more risky behavior. Chapter II uses hospital discharge data (NIS) to estimate avoidable hospitalization in order to assess primary care utilization. The result shows that less primary care was consumed, which leads to more avoidable hospitalization but health may have been improved by using more hospital care. The results from both chapters imply potential ex ante moral hazard among young adults in the policy targeting age group. Thus, chapter III uses accident records data (FARS) to examine the impact of the health insurance expansion on traffic fatality for young adults, to see whether young drivers perform ex ante moral hazard through risky behavior like drunk and/or reckless driving after they get covered by the health insurance expansion policy. Primary result shows that there is an increase in traffic accidents and fatalities for those younger adults as a result of the ACA dependent coverage expansion.