THE Bay Area Rapid Transit system (BART) has many characteristics of a huge social experiment—in vivo, as it were. Key element in a bold scheme to structure the future of the San Francisco region, BART was to stem the much  feared decline of the older metropolitan centers, while helping to give coherent order to the exploding suburbs. By offering a superior alternative to the automobile, BART was to make for congestion free commuting. If successful, it would provide a model for rationalizing transportation and metropolitan development elsewhere.