has 15-minute headways. Fleet utilization ranges from 16 trains (96 cars) on weekends to 24 trains (144 cars) at peak hours. The Ashmont and Harvard branches were both built with automatic block signaling and trip-stop train protection, while the Braintree and Alewife extensions of the 1980s were constructed with Automatic Train Control (ATC) using audio frequency cab signaling. In 1985 the entire Red Line was converted to the new cab signal standard with any remaining interlocking towers being closed with a relay based centralized traffic control machine being installed in a dispatch office at 45 High Street. This in turn was replaced in the late 1990s with a software-controlled Automatic Train Supervision product by Union Switch & Signal, subcontracted to Syseca Inc. (now ARINC), in a new control room. Subsequent revisions to the system were made internally at the MBTA. Scheduled headways were as low as 2 minutes after the 1928 extension to Ashmont. When Stadium station was in use for Harvard football games, headways as low as 1 minutes were used. Ridership peaked around 1947, when passenger counters logged over 850 people per four-car train during peak periods. After the conversion to ATC, throughput in the downtown corridor was 13 trains per hour or a little less than 5 minute headway which gives a maximum capacity of 20,280 passengers per hour. In October 2018, the MBTA awarded a $218 million improved signal contract for the Red and Orange Lines, which will allow 3-minute headways between JFK/UMass and Alewife beginning in 2022. The decreased headway will be achieved through increased vehicle performance, an upgrade of the existing ATC system to use higher performance digital components and a reduction in the length of signaling blocks to 500 feet. During snowstorms, the MBTA runs an empty train during non-service hours to keep the tracks and third rail clear. The Red Line experienced major service disruptions in the winter of 2014–15 due to frozen-over third rails, leaving unpowered trains stranded between stations with passengers on board. Rolling stock The Red Line is standard gauge heavy rail. Trains consist of mated pairs of electric multiple unit cars powered from a 600 V DC third rail. All trains run in six-car sets. All cars are roughly long, wide, and have a platform height of above the top of rail. Rolling stock is maintained at the Cabot Yard in South Boston. Yard leads connect to the