No NPS shuttle when I was there and when I inquired the Ranger did not give me the impression they could take me thru. That said, if there's a more conducive place to hitch a ride, I can't imagine where it would be. Even as a 58 y.o. guy who hadn't shaved recently and probably looked a little rough after 3 weeks on the road I had no trouble. With all those cars at a stop, if they have room for you and the bike it's harder to wave you off then to say yes.
Before I got there I was under the impression that they had traffic going both ways except when a large RV or tour bus came along and they would then make the tunnel one way for that vehicle to pass. That turned out not to be true and after seeing how narrow the tunnel is and how many large RVs and tour buses go thru, I didn't see any way that could ever be the case. And it was so regulated that even on the morning when I left and there was much more traffic leaving then entering the park, they still kept the tunnel open in either direction the same amount of time (say 15± minutes) each way instead of going to 10 minutes one direction and 20 minutes in the busier direction.
RE the article you linked to : I don't know where the park rangers were when these guys rolled up because they were standing sentry when I got there and they made sure to let me know in no uncertain terms to not even think about riding thru. Be that as it may, that was an exceptionally stupid move on the riders part to go in there w/o a proper front light. There was several places in the tunnel where there was daylight but overwhelmingly it was Dark and not straight with a pretty good down hill slope.
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