I drove through the Baltimore Harbor Tunnel yesterday while using autosteer. About halfway through the (1.4 mile long) tunnel, it suddenly screamed at me to take over. I had both hands on the wheel and was actively engaged anyway (narrow lanes and close walls!) so I did and it was no sweat. A message on the instrument cluster said something to the effect of, forward radar visibility reduced. After exiting the tunnel I tried to reengage autopilot, but it just beeped at me and gave me the same message. This applied to both autosteer and plain TACC. I thought maybe I had hit something that damaged or obstructed the radar. Then a couple of minutes later, it came back on and worked fine for the rest of my drive home. My speculation is that the radar got confused in the tunnel environment, then took a couple of minutes afterwards to make sure everything was working OK before it was willing to resume. Has anyone seen this happen in similar circumstances, and does anyone know if my speculation is at all correct?