From San Jose to just north of Santa Clara, ACE uses the Caltrain main line, shared with Caltrain and Amtrak service. From Santa Clara to Stockton - the majority of the route - ACE runs on Union Pacific Railroad freight lines. From Santa Clara to Newark, ACE uses the Coastal Subdivision, then the Niles Subdivision to Niles. From Niles to Stockton, the line uses the Oakland Subdivision.