The reason for this is economics. If you look at the map at the beginning of the video (or Google Maps), you will see I-40 bend around Shamrock (and every other small town in Texas) while the historic Route 66 continues into the town as I-40 Business Loop — obviously saving the state money in building new highways when they can simply upgrade existing ones — in this case, Rt 66.
On My Way – Kevin MacLeod (incompetech.com)
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