There's really no incentive for Union Pacific to want more Amtrak service. The rate formula isn't in UP's favor, and Amtrak can't really afford to pay more if wanted to for a new route.
If a private operator is willing to pay a premium above what Amtrak's operating agreement rates are, UP might actually listen. They can't technically operate their own service because of their buy-in on Amtrak, but I doubt there's anything that says they can't invest in a joint venture that isn't directly competing with Amtrak. DAL-HOU would fit that description.
UP already owns the tracks between downtown Dallas and downtown Houston, and Brightline's equipment is portable. They could start something up within months, and have a lot less to lose if it failed. It would be a 4 hour trip, which isn't shorter than driving, but because it would be downtown to downtown with links to existing light rail networks, the time disadvantage over driving might not be as much of a concern.
Another advantage of the UP's existing network... they could just as easily do Dallas-Austin and Dallas-Houston via Hearne, and the Hearne-Houston leg goes via College Station...
If they were to start up, it might kill investor interest in TCR, and without US investment, it's going to be a hard sell to the regulatory agencies.
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