I rode a really scary tunnel once on the same '87 France trip mentioned at my post above. It was into the town of Val d'Isere. Didn't get a picture. Here's Google's.....

https://goo.gl/3W3AjZ

Although lit, the tunnel was long and curved so you couldn't see the end, and was a main road with traffic. My method to get through safely was to wait at the entry for an approaching car and ask them to follow as an escort. As I recall, being in France, I did this with gestures to communicate the request. Got the thumbs up from the helpful driver and took the plunge! It was still a white knuckle experience. A truck with noisy exhaust was behind my escort making the trip even scarier. Glad I didn't get a flat!