Nobody can give you a correct answer on your question I think. For tunnels there are à few tricks so they work a little better. I don't think someone did that in Brussels...

It was one of the things I wanted to take up to the waze meeting. If I manage to join, I'll talk about this.

My ideas :
* Have waze automatically detect tunnels or areas were there is no GPS coverage : most of the time this is feasible because you still have data connection and all wazers should loose GPS in the same area (so detection is relatively reliable after you have this lack of coverage for 3 or more wazers)
* Have waze notify you you're entering such an area a few hundred meters before it starts (warning you that waze won't be able to follow you)
* Notification should also include instructions to follow the route when there is no GPS coverage (for instance : "In 300m, a non-covered GPS area begins. In 800m, in the non-covered GPS area, turn left and in 1km, in the non-covered GPS area, exit right.", of course this is a proposal which can be adapted). It can lead to quite long instructions, but is better than nothing (which is the case currently).
* It is possible to detect if the lack of coverage corresponds to a tunnel based on the height of the road in the map.

Also :
* Very short and easy workaround in the meantime : make a warning sound when there is no GPS reception. It is not the case currently, so that when you have turns in a non-covered area and you don't have your smartphone in front of you, you don't get any notification and you tend to always go straight...