And yet we "simply" build new highways all the time, which consume a lot more land than railways do.
Elsewhere the US continues build tons and tons of roads. According to the Bureau of Transport Statistics the US highway system went from 4,050,717 miles in 2009 to 4,171,125 miles in 2019. This is a delta 120,408 miles, or an increase of 2.9%.
The 710 might be an interesting example, but it's not exactly indicative of a trend.
But ultimately the expansion of the highways has downstream effects - state will buy new land, build new roads, etc. as density flows out. If you have a two lane highway going into a city and it's congested, and then you expand it, more people move out of the city or more further away - obviously someone is building new roads or expanding existing ones as that occurs.
Actually correlating this down to individual routes in an exhausting endeavor, given all the places these could be recorded. But I found that we did designate 7 new highways in the past 10 years, including I-14, I-11, I-87, I-41, I-42, I-2, and I-22.