I was looking at Hemmings Street Scene blog (http://bit.ly/18iqpdl) (which, by the way, occasionally turns up a great highway photo from the '50s through the '70s) and I came across this photo of the Schuylkill/Vine interchange in Philadelphia.
The caption lists the date as August 1973, and the lower portion of the Schuylkill is still signed I-676, as it was originally numbered in 1964 (and I-680 before that). FHWA's Rambler (http://1.usa.gov/12I6G8h) indicates that the 76/676 swap was approved in August of 1972, although Jeff Kitsko says that the change didn't take place until 1974.
And note the really terrible kerning on the 676 shield. It looks almost like sixty-seven six.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fbit.ly%2F17cjQOp&hash=f7c552351d9ac59ee4bc75f498a78e95cc96116b)
Here's the original article (http://bit.ly/1dM7s8W).
Wow, does that bring back memories!
Wow, old car porn. :sombrero: