Complex sentence: In 2003, the District introduced a San Mateo-Hayward Bridge route, Line M, to connect the BART stations of Castro Valley and Hayward with Foster City and San Mateo's Hillsdale Boulevard Caltrain station.
Split into simpler sentences: In 2003, the District introduced a San Mateo-Hayward Bridge route. Designated as Line M, the service connected the BART stations of Castro Valley and Hayward with Foster City and San Mateo's Hillsdale Caltrain station.