At the times it ran, at least in the 1950s toward the end, it didn't fit into any rational passenger schedule. Left SF early (6ish?) and returned well after dark. So "running extra" fit the operation fine.

I vaguely recall dragging down to 3rd/Townsend well before dawn, stopping someplace on the Peninsula (Palo Alto?) and San Jose, then moseying on south (asleep by then) looking out the window someplace near Chittenden (mountains pretty close in dim light) then finally waking up someplace in Santa Cruz County. Total running time must have been 4hr or more - arrived SC late morning but not lunchtime. The train dropped everybody in front of the Boardwalk, then went away to turn and park for the day. Came back late afternoon - 5ish? - and arrived back in SF at about bedtime. Of course, the sun never came out but that's OK - we all got fogburns and did rides at the Boardwalk, and I think the "Plunge" was still a swimming pool so we could get into some water that wasn't freezing. Definitely had diesels but I have no idea what type (hey, I was 5 or 6 at the time!), and the cheap seats coaches we were in were single level and uncomfortable (it's amazing what a sleepy 5-year-old can put up with) so probably Harrimans off commute duty.

If the Watsonville-SC track were Class 2, you could probably still do it in about the same running time, but UP would never allow it and who would ride it (4+ hours from SF for a trip you could do in 1 1/2-2 driving even with a fair amount of traffic?)? You'd probably need something a little more posh than commute cars on runabout for the weekend. Also remember, cars were not as reliable back then (gas was harder to find out of town, and would you make it over 17 without boiling over or burning out the brakes?) and the Bayshore Freeway was new and not really complete, while railroads *were* reliable even if running extra.