ORLANDO — Amtrak’s decades-old monopoly on intercity passenger rail travel will fall in the coming weeks when Florida becomes home to the fastest American trains outside the Northeast Corridor.

Brightline, the only private passenger railroad in the country, is slated to open its newest station here later this year, providing a train connection between Orlando International Airport and South Florida in three hours. Meanwhile, work is progressing on high-speed projects in Western states and Texas, and Amtrak is eyeing its biggest expansion in 52 years.The 5 higher-speed rail projects taking shape in the U.S.

Two years after the infrastructure law began pumping $66 billion into the nation’s aging rail network, domestic passenger railroads are showing their greatest signs of strength in generations. Amtrak’s singular grip on transporting U.S. rail passengers is slipping as private companies, states and the federal government look to fast trains as environmentally friendly alternatives to traffic-clogged highways, while developers promise speeds rivaling those in Europe and Asia.

Amtrak says it views other rail providers as complementary to its offerings, coming as the nation’s longtime passenger rail — newly flush with billions of federal […]