- Require less specialized crew training, and don't require as many crew members to be equivalently specialized (though you'd be surprised at the depth of training that's still required to crew an Amtrak).
- Can stop, and stop at offloading/transfer points, more easily than planes. In the event of issues this further increases flexibility of the system.
- Have considerably more built-in redundancy than planes, and some built-in swap-ability of components during a trip by removing or replacing cars. I say "some" in italics because I've recently been ... er, very directly acquainted with how critical a single pantograph failure can be to an entire rail line.
- Might, if implemented via state-operated rail or state-sponsored monopoly, offer the ability to replace, deploy, or reroute entire trains in the event of unexpected capacity/mechanical issues. This advantage is a bit of a wash, though, in that we'd probably have more redundancy in air travel if there were fewer larger carriers (this isn't guaranteed and trades off with other issues, but redundancy/flexibility is an advantage of consolidation).
- Are mechanically simpler than planes, and thus require less overhead before being deployed and have fewer "no-go" inspection conditions that can introduce unexpected unavailability.