So let's apply this outside of Amtrak and to a service whose need for a Conductor is highly suspect: TriMet's WES.

14.7 miles long. Runs from Wilsonville to Beaverton, 27 minute running time, 10 minute layover. 27 minutes from Beaverton back to Wilsonville, 26 minute layover. Crew is on duty about four hours in the morning and again four hours in the afternoon, there are three round-trips (one crew only does two round-trips) per shift for a total of 81 "en-route minutes".

Each train, whether it is just the single DMU, or has one trailer (for a total of two cars) currently has an Engineer and a Conductor. The Conductor may, or may not, inspect for fares, but the Conductor is a GWI (Portland & Western) employee and not TriMet so the Conductor's legal recource for a fare evader is to either kick the rider off at the next station or call for police. TriMet Supervisors (Fare Inspectors) and Transit Police do not routinely patrol WES; and WES crews do not have direct radio access to TriMet supervisory personnel (since GWI dispatches the railroad) - presumably they probably have a direct phone number to TriMet Rail Control for police calls if needed.

What, other than FRA requirement, is the justification for Conductors on this extremely short (both in miles, and train length) service? Ottawa's O-Train succesfully shows that a similar "commuter rail" service can safely operate with just one person; further WES is already equipped with cab and wayside signalling, ATS and I believe even has most if not all of the workings of PTC. So there is already an extremely high level of supervisory control in the event a sole crewmember is incapacitated unlike most rail services in the U.S.