In 2021, over 31 million passengers rode passenger trains in the United States, according to data from the Federal Railroad Administration (FRA). Amtrak, the national passenger railroad service in the U.S., accounted for the vast majority of these passengers, with over 30 million riders on its various train lines. Commuter rail services also saw significant ridership, with nearly 1.4 million passengers using commuter trains each weekday.

Overall, passenger rail travel in the U.S. has been on a steady incline over the past several years, with ridership increasing by an average of 5.5% each year between 2011 and 2019. This growth has been attributed to a number of factors, including rising fuel prices, increased urbanization, and expanding public transportation options.

Some of the most popular passenger train routes in the U.S. include:

* The Northeast Corridor, which runs from Boston to Washington, D.C., is the busiest passenger rail corridor in the country, with over 12 million riders per year.

* The California Zephyr, which runs from Chicago to San Francisco, is a long-distance train route that offers scenic views of the Rocky Mountains and the Sierra Nevada.

* The Empire Builder, which runs from Chicago to Portland, Oregon, is another long-distance train route that offers stunning scenery of the Midwest and Northwest.

In addition to these popular routes, there are numerous other passenger train services operating in the U.S., connecting smaller cities and towns with larger metropolitan areas. These services provide an important transportation option for people living in rural areas or for those who prefer not to drive.

Overall, passenger rail travel in the U.S. is a growing and important part of the country's transportation system. With continued investment and expansion of passenger rail services, more and more people are expected to choose rail as their preferred mode of transportation.