I actually have a vague memory of someone else posting a photo sequence like this of a HAZMAT escort through Cumberland Gap Tunnel, but I was there for one last week and thought I'd share the photos I took, for what they're worth to anyone:
(https://farm1.staticflickr.com/258/19568509256_1ca5a65749.jpg) (https://flic.kr/p/vPcJ3C)
(https://farm1.staticflickr.com/364/19599000091_baf98e38a6.jpg) (https://flic.kr/p/vRTZUF)
(https://farm4.staticflickr.com/3756/19408082729_4aa8d07ce3.jpg) (https://flic.kr/p/vz2uQ2)
(https://farm1.staticflickr.com/336/18972090024_10246be079.jpg) (https://flic.kr/p/uUuVoq)
Like the tunnel portal more than the sign. However interesting way of stopping those said vehicles.
This is quite a good system for HAZMAT Escorts.
I've come upon the tail end of a tunnel closure for a HAZMAT escort before there.