Skipper, can you please stop creating a new topic every time you think of a new trivia question? We already have an official trivia thread, and you have now created four topics called "Dukes Trivia" in this forum in the last year, and another four topics for questions about individual episodes. Forums don't work nearly as well when the information is scattered in different places. Take a little time to see if the topic already exists, and use the search function to see if the information already exists.
I'm guessing that the answer you're looking for is that 'Duel' and 'Witness for the Persecution' both feature the tunnel on Soledad Canyon Road. You can see a couple of screengrabs from the latter in the Hazzard Square thread.