During the car / boat chase in Louisiana, the road they travel on shows the newly introduced full yellow road striping. Although still pretty rare at the time to see full yellow striping (MUDCT introduced it in late 1971), you'll notice that there are no white lines underneath. (Later scenes show that this road had just been re-surfaced, and parts have no striping at all. Hence, it was most definitely plausible to have had the full new markings present and no trace of the old ones.)
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