TACC Disabling in Tunnels. Why?

The last week or so I've driven several times through a tunnel near where I live (about 1-2 miles long, descending about 80 ft below the surface of the Chesapeake Bay). Anyway, like clockwork, TACC always disables within about 30 seconds of entering the tunnel. I get a "Cruise not available" message. This has happened 3 times (every time I've driven through it).

My question is--why? What about the tunnel is shutting down the cruise? The driving and road condition isn't any different.

Two theories:

1) The increased pollution from ICE exhaust in the tunnel is causing issues with the radar. (This seems most plausible, although I have a hard time believing that exhaust would cause enough of a radar signature to cause issues).

2) The camera is somehow involved in the TACC system, and it's getting confused by the lighting conditions.


Any thoughts?

By the way, I've read that a lot of people reboot the touchscreen when they get a "cruise not available" message while using TACC. I've found that simply toggling cruise off and then back on (using the button at the end of the stalk) is sufficient to reset the system and begin using it again (given that the condition causing the error has gone away).

Ok, going on the reflection on walls theory, has anyone lost TACC simply going through an area that has a high wall on one side of your lane? (The tunnel I was driving through was two lanes each direction, so only a wall on one side.

For the record, I drove through several tunnels with TACC active yesterday, and it performed without issue in all of them. So it looks like this issue has been fixed in a recent software update.