This research project aims to optimize subsidy incentivization strategies by applying Equity Credit Methodologies among transit service providers in selected regions, in this case, the Washington Metropolitan Area, in order to increase accessibility. It explores the design of a fair subsidy distribution system to improve transportation equity and social well-being. In the United States, unequal access to the transportation system exacerbates social inequality. At the same time, heavy reliance on cars has also exposed the inaccessibility of public transportation, bringing side effects such as severe air pollution, ultimately leading to climate change and congestion. To close the gap between accessible transportation options and residents needing these services, our research focuses on how to design a fair subsidy distribution system for each income group, thereby optimizing transportation equity improvements as well as revenue for transportation service companies. We aim to construct a comprehensive framework that considers factors such as demographics, economic status, geographical location, and transportation accessibility of target areas and further analyze the impact of the proposed subsidy allocation. Our procedures include designing optimization models, collecting data, applying the models, and performing sensitivity analyses. Ultimately, the goal is to incorporate carbon credit measures into the subsidy system by allocating individual emission credits to citizens using public transport. This will allow companies that need carbon credits to receive them from individuals, thereby paying for subsidies from transport companies or governments. This comprehensive approach will not only help policymakers with subsidy allocation but also reduce inequalities in transport access. It will also reduce emissions and provide a model that can be replicated in cities throughout the world.