Thanks to everyone who contributed to this project, I think it's pretty much complete for the US. There's data logged for 47 states + DC, and the remaining three states (MT, VT, WY) have no existing six-lane mileage. It's imperfect, but still a great resource and much, much better than anything that existed previously.
Sorting by mileage then country provides some interesting data to parse through:
https://travelmapping.net/user/?u=6lane&units=milesUnsurprisingly, Ohio stands out as the gold standard for six-laning. It's the only state with a population under 20 million that comes particularly close to 1000 miles of six-lane freeways logged, although that may be a bit skewed if the I-80/I-90 overlap gets counted twice. Even so, it's well ahead of next-place Georgia and actively adding to that with widening projects on I-70 and I-71.
Another interesting note: a state's six-lane mileage ranking tends to track pretty closely with its population ranking. 9 of the top 10 are the same in both categories, with NJ replacing PA in the six-lane mileage category. Most of the states at the bottom are also unsurprising.
PA has a surprisingly wide variance, being #5 in population but #23 in six-lane mileage. I was stunned that PA has only about 1/3 as much six-lane mileage as NY, given that PA
feels like it has more *rural* six-lane mileage than NY (or am I just putting too much weight on the widened Turnpike segments?), but I guess the lack of mid-sized cities (in which NY stacks considerable mileage upstate) plus Pittsburgh and Scranton not having anything with a consistent six-lanes really skews PA down the list.
