in the 2000s, bart was expanded to reach san francisco international airport. it now goes as far as millbrae. two other branch lines have opened since then. in 2014, bart opened a short line to oakland international airport that uses trains pulled by cables. an extension of the pittsburg line to antioch, which opened in 2018, uses diesel multiple units on standard gauge tracks instead of the electric, broad-gauge trains used on the main lines. a project is also going on to expand the southern main line into san jose. the entire extension was supposed to be completed in 2018. instead, the first new stations were opened on june 13, 2020 after breakdowns in communication and testing with the line.