wider doors to allow faster boarding at busy stations, and can allow wheelchair access even if one of a pair of door panels fails to open. The MBTA rebuilt Track 61 to serve as a test track for the new Red Line cars. In December 2016, the MBTA opted to purchase additional identical cars from CRRC, allowing replacement rather than costly refurbishment of the 01800 series cars. The second order is for 120 cars costing $277 million, with an option for 14 additional cars. Combined, the 2014 and 2016 orders will provide a single common fleet for the entire Red Line, with enough cars to eventually run 3-minute headways at peak. Replacement of the signal system is expected to be complete by 2021 on the Red Line; the total cost is $218 million for both the Red and Orange Lines. The first trainset of new cars entered revenue service on December 30, 2020. The cars were taken out of service on March 16, 2021 after a CRRC car on the Orange Line derailed. After investigations were completed, they returned to service in January 2022, at which point an increased number of deliveries was expected during 2022. The cars were pulled from service again in June 2022 after a battery failure; they returned in July 2022. Production delays became apparent in 2019, and then factory shutdowns and staffing limitations caused by the COVID-19 pandemic delayed projected final delivery to 2024, with subsequent issues with staffing, supply chain, and delaying expected completion to summer 2025. The CRRC contract specifies a penalty of $500 per car per day of delay after September 2023; as of September 2022, 12 cars had been delivered. Art and architecture The MBTA pioneered a "percentage for art" public art program called Arts on the Line during its Northwest Extension of the Red Line in the late 1970s and early 1980s. Arts on the Line was the first program of its kind in the United States and became the model for similar programs for art across the country. The Kendall/MIT station features an interactive public art installation by Paul Matisse called the Kendall Band, which allows the public to activate three sound-producing machines utilizing levers on the wall of the station. Above the tracks at Alewife hangs a series of red neon tubes called The End of the Red Line, by the Boston artists Alejandro and Moira Sina. Many