One of the most common questions in transportation planning is determining if existing mobility resources connect people to destinations they need to reach in a reasonable amount of time. While the basic premise of the question is easy to understand, at a regional level, this question is quite complex. To assess the degree to which a network meets the needs of some or all of the people living in a region, we need to iterate the analysis over time and space. That is, instead of analyzing how far one person can get on transit at a particular time, we need to determine how far people across the county can get at any one time. Until now, this question has been beyond our ability to answer as available methods required too much staff time or computing time to implement. Now, the R programming language and the r5r package allow analysts to iterate over the transit network efficiently. This documentation will outline current thinking regarding transit accessibility at King County Metro and will show intermediate results. The goal is to show each step and assumption of the current method and to outline potential alternatives.