The T Third Street is a Muni Metro light rail line in San Francisco, California. It runs along the east side of San Francisco – primarily in the median of Third Street – from Sunnydale to the Market Street subway. It is interlined with the K Ingleside line, forming a single service running between Sunnydale and Balboa Park. The line serves 21 surface stations, all of which are accessible. Most of the surface portion of the line runs in dedicated median lanes, though two portions operate in mixed traffic.