The problem of accessibility to public transit is a well-documented problem in transportation theory and network literature known as the “Last Mile” problem. A lack of first and last mile specific transit services impairs access to public transit causing commuters to opt for private modes of transit over public modes of transit. This paper analyzes the implications of a shared autonomous vehicle (AV) taxi system providing last mile specific transit services in terms of environmental, cost, and performance metrics. Conventional public transit options along with a hypothetical last-mile shared autonomous vehicle (SAV) system are analyzed for transit between Ann Arbor and Detroit Wayne County Airport for life cycle energy, emissions, total travel time, and travel costs. In the case study, energy savings from using public transit options with AV last mile service were as high as 39% when compared to a personal vehicle (parking) option. The results suggest that an AV taxi service providing last-mile transit services could greatly enhance the sustainability of transit by influencing mode shift from private modes of transit to public modes of transit. Wait times associated with public transit options as well as high AV technology costs could be obstacles for such a last mile service.