CSX could begin construction on Boone tunnel widening in 2022. CSX When railroads were built, clearance concerns were limited to boxcars, hopper cars, and other general freight cars. At the time, no one envisioned that one day, clearance would be required for containers and truck trailers sitting in well cars or on flat cars would require higher clearance than the original tunnels allowed. For nearly two decades, railroads, particularly those in the east, have worked extensively to raise the clearance in the many tunnels on their lines in order to take advantage of the intermodal boom and remain competitive with interstate highway routes.