I once drove in a rental golf cart (14MPH?) from Liberty Park up Buena Vista to the shopping center on 42 and it took around 45 minutes.
Using a very unscientific method, I'd guess that distance to be around 3/4 of 12 (I'm using 12 because I didn't maintain full speed the whole way, and because 12 is easier to divide into quarters) and I'd guess it was 9 miles. Add another mile or so from Liberty Park south to 466A, and I'd guess a total of 10 or 11 miles.
That's fairly close to the measurements above.
