The exurban areas of Australia’s three largest capital cities. For example, the Central Coast line north of Sydney has half-hourly electric intercity trains interoperating with freight on a line that extends 165km from the city. Melbourne and Brisbane have similar lines radiating out to regional areas.

Within the Sydney metropolitan area, commuter trains are operating among freight trains at 5-15 minute frequencies, though with dedicated freight bypass lines in some places.

One issue in the USA, alongside private ownership of the rail lines, is oversized freight trains and resulting overbuilding required of passenger trains for crash safety. Unfortunately that rules out high-performance EMU designs as used in other countries. I believe Caltrain had to get an exemption for their ongoing electrification upgrades.

It’s much easier to double, triple or quadruple track the beat up American railroad infrastructure if it was in public hand, working to maximise capacity for the whole market, rather than just every piece of track being used to maximise profits for a single company, acting as a moat to ensure as little local competition as possible.