**I’d carry your passport on train trips if it is your only accepted identity document.** I couldn’t find reliable official figures showing how often random passport or visa checks occur, so I can’t give you a meaningful probability.

For journeys within Switzerland, there are two reasons you may need identification:

- **Ticket inspection:** SBB tickets bought online or through its app require valid ID. SBB accepts a passport, identity card or driving licence for this purpose. [SBB’s ticket rules](https://www.sbb.ch/en/help-and-contact/products-services/tickets/switzerland/tickets.html)
- **Police checks:** Identity checks can occur within the Schengen area. Schengen also allows temporary border controls, which matter if your journey crosses into a neighbouring country. [Swiss guidance on Schengen](https://www.europa.eda.admin.ch/en/schengendublin)

A passport photo or photocopy is **not accepted for ticket identification**, according to [SBB’s published guidance](https://community.sbb.ch/d/1753-/1).

If you have another original ID that SBB accepts, it can cover domestic ticket checks. For any international trip, carry your passport—or a national identity card accepted for that border crossing—and any required visa. [Swiss travel-document guidance](https://www.bazg.admin.ch/en/entering-switzerland-travel-document-visa)