The platforms are near the center of the shell, with the outbound track on the east side ad the inbound track on the west side. At 105 feet below ground level, the outbound platform is the deepest in the MBTA system. Porter's unusual depth is due to the MBTA's decision to build the station in bedrock rather than soft clay, saving time and money in the construction process. Passengers reach Red Line platforms via a series of escalators, stairs totalling 199 steps, or a set of elevators. The longest single span of the escalators is , the longest in the MBTA system. In 2005, a man was killed when his sweatshirt tangled in the bottom of the escalator. Porter is fully accessible; elevators lead from street level to the mezzanine with its accessible bathrooms, to the commuter rail platform, and to both Red Line platform levels. Although most of the commuter platform is low, there is a "mini-high platform" – a one-car-length high section – that allows level boarding. The station was originally built with three elevators: from Elm Street to the fare lobby, from the lobby to both Red Line platforms, and from the lobby to the commuter rail platform. As a result of a 2006 settlement of a lawsuit filed by the Boston Center for Independent Living and a group of individuals, the MBTA installed additional elevators at Porter and four other busy MBTA subway stations. The three existing elevators were overhauled, and two redundant elevators were added, in a $12 million project. The elevator to the Red Line platforms was out of service for construction from March 21, 2011 to June 22, 2012; an accessible shuttle bus ran between Porter and . The elevator to the commuter rail platform was also taken out of service from December 9, 2011 to July 2012; a shuttle bus ran between , Porter, and . An elevator from Massachusetts Avenue to the lobby opened later that year, followed by an overhaul of the existing street elevator; the redundant Red Line platform elevator was completed in 2013. As a part of the Red Line Northwest Extension, Porter was included as one of the stations involved in the Arts on the Line program, devised to bring art into the MBTA's subway stations in the late 1970s and early 1980s. It was the first program of its kind in the United States and became the model for similar drives for art across the country. Six works, five of which remain, were placed at Porter:  Porter serves several MBTA Bus local routes: The 77 and 96 run on Massachusetts Avenue, while the 83 turns from Somerville Avenue to Massachusetts Avenue at Porter Square.