[Alberta's Child]

Rail is not the single biggest mode of freight transport in the U.S. at all.

Nationally, trucks carry about seven times more tonnage than railroads in the U.S.

USDOT -- Freight Tonnage by Mode

Having said that, I should also point out that there are no transportation infrastructure projects that can change this. Trucks dominate our freight transportation system because they are so flexible and can travel almost anywhere. Very few business establishments in the U.S. have rail sidings that serve them directly.

[Spktyr]

Another DOT site has a different take on that: https://www.fra.dot.gov/Page/P0362

How Freight Moves

Freight is moved by rail, water, pipeline, truck, and air. The rail network accounts for approximately 40 percent of U.S. freight moves by ton-miles (the length freight travels) and 16 percent by tons (the weight of freight moved). [5]

On the rails, in general, bulk freight, such as grain and coal, ships in rail cars and consumer goods, such as items found at a neighborhood store, ship in containers or trailers called intermodal traffic. Intermodal traffic refers to the transport of goods on trains before and/or after transfers from other modes of transportation such as planes, vessels, or trucks. It has been the fastest growing segment of the freight rail industry since 1980.