Here is a relevant resource on such rail electrification topics: https://www.caltrain.com/media/21596/

Q: What will happen to service to Gilroy?
A: The current Caltrain Electrification project only includes electrification to a point approximately two miles south of
Tamien Station in San Jose. Caltrain will continue to provide diesel service to Gilroy.
Q: Why not electrify south of Tamien Station?
A: Caltrain does not own the southbound right-of-way beginning two miles south of Tamien Station. Union Pacific Railroad owns this section of the corridor. 