Theoretically, with adequate length sidings spaced evenly (time wise), an equal number of trains in each direction could be run, following each other by the run time to the second next siding plus start up times. Thus if the run time between any two adjacent sidings was 10 minutes, with a 5 minute start up time; then trains in each direction could theoretically run every 30 minutes.

Of course, this is a maximum. Many practicalities get in the way though, to make it rather unsustainable for very long. Though Sacramento Regional Transit manages single track 15 minute headways on a siding spacing of about 6 minutes.

There are also tricks that can be used on single track stretches that aren't too long (about an hour run time); such as fleeting all the westbounds for a while and then fleeting the eastbounds. If the signaling system is properly spaced (much of UP's is not), trains could run 10 to 15 minutes apart, depending on train length and cumbersomeness.

Yes long trains do eat up trains per hour capacity. And at some point, overall haulage capacity goes into diminishing returns - but I digress. At an ideal 2 per hour in each direction, 48 trains per day could theoretically be run in each direction - 96 per day total. So, to answer the question; Yes, 40 to 50 total trains per day and more, can be handled with proper signal system design and adept dispatching.

And let's not forget the role responsive train crews would play in achieving high capacity single track operations. The more promptly they can get a train moving again after a meet, is of paramount importance to high capacity railroading.

I hope that answers the question

OPB