This is the way that Sacramento and San Diego went initially, later expanding to double track when the funding permitted. It should be considered in other settings as well for cost savings.
From the Rocky Mountain News:
The project originally included two tracks on that final segment. But in 2005, faced with cost increases, RTD decided to cut service on the outer leg to trains every 15 minutes instead of every five minutes. That allowed RTD to reduce the number of train cars it had to buy, saving more than $12 million.
Then last year, with costs still escalating sharply, RTD realized it could run 15-minute service on a single track west of the federal center by including a short passing track near Red Rocks Community College. The move saved another $33 million.
Jefferson County planners and commissioners objected, saying if RTD's ridership estimates are wrong and more growth occurs than anticipated, RTD would be locked into having inadequate track capacity to handle it.
Jeffco had asked RTD to consider running 10-minute trains, which would have required a second passing track.