I rode it with a full load last September while crossing the state. 32c Continental Touring IIs. A little bumpy/choppy in places, but generally no problemo. No way you need 40s. I started heading east in the westbound lanes because on the Breezewood end they were in better condition. At some point I switched to the eastbound lanes. A strong light for the tunnels is highly recommended. I used a 120 lumen head lamp. Encountered virtually no debris in the tunnels. One tip someone gave me before the trip was to simply follow the median stripe. Worked out well. Note that there is a pretty good crown in the second tunnel, which means you cannot see the light at the eastern end until you are most of the way through. Not long after the second tunnel, you will see some Jersey barriers on the left. You cannot go much farther east than that as the bridge over Pump Station Rd. has been removed.
To get there, head east on U.S. 30 from the commercial part of Breezewood. A few hundred feet after you cross under I-70, make a left onto Tannery Rd. You will immediately see a small, dirt parking lot. Park there, walk you bike up the well worn path in the berm and you will see some Jersey barriers marking the entrance. Needless to say, bring enough food and water. If it's chilly, bring a jacket. It's very cool inside the tunnels. Outside it was in the upper 80s and humid when I rode it. The tunnels made for a nice break from the heat. Even at the mouths of the tunnels it was like standing in front of a central air conditioner. I didn't want to leave the comfort. Was there on a Tuesday afternoon. Saw no other riders and one young couple walking. There is a Sheetz convenience store in Breezewood if you need snacks and/or water.