In this study, we analyzed and projected the future toll revenue of privatized expressways in Korea as their concession periods expire to propose legal and institutional improvements for effective public reinvestment. We focused on 17 expressways that are privately operated and currently in service as of late 2023. We constructed multiple scenarios extending from 2031 to 2050 to anticipate how toll revenues might evolve over time. Although these projections could prove inaccurate or anachronistic, we considered a range of outcomes. Legal frameworks such as the Toll Road Act and the Private Investment Act were also examined to explore whether reinvestment of toll income would be legally viable after the end of the concession agreements. We considered a scenario in which toll rates remained unchanged after the concession expired. In such a case, projected net revenues might reach roughly KRW 1.319 trillion by 2031 and increase to about KRW 10.146 trillion by 2050. That value is roughly KRW 11.8 trillion over two decades—a considerable sum. To put this in context, as of the end of 2023, this figure would represent a substantial slice of the total market capitalization of private expressways. On the other hand, lowering the tolls to match those of public roads would cut the revenue nearly in half. Of note, current laws mostly restrict toll income to basic maintenance; any broader use would require legislative reform. Legal revisions are needed to allow the reinvestment of surplus toll revenue from expired concessions into new SOC projects. Additionally, measures such as toll adjustment and integrated toll system management are recommended to enhance public benefit and investment sustainability.