Limited bus service, with limited passenger capacity, is provided only at San Jose Diridon, Palo Alto and Millbrae stations.
The buses will not run into San Francisco as there will be no stops and no bus service north of Millbrae, Caltrain said.
The shutdown is part of Caltrain's work to electrify the railroad with trains that are supposed to be faster, cleaner and more efficient.
The new trains are set to roll out in September.
Bay City News contributed to this report.
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