It does work long term? Extra lanes doesn't do much, no, but more roadways/bridges have shown to reduce traffic, depending on where traffic really wants to go. Adding more lanes didn't do much because everyone's going that same way. Add another road, you'll have less people going that way. I've played Cities Skylines (which doesn't mean much), but adding more lanes does change a bit, but definitely not enough at all. For example, have one highway in a city for people to get in and out. You'll get traffic.

Adding a lane won't change anything because it will just allow more cars to fill in, but still traffic. Add another highway on the city's border going a bit of a different direction of that highway, but still having a similar route, more cars that are closer to that roadway, or people living near said roadway, are more likely to go on that route, reducing traffic on the other highway.

Say that you live on LI, now you have to drive all the way down through NYC, to get to Connecticut, instead of simply just going to Connecticut. Add an extra lane on the bridges, it won't change much, you're still going to add on to the rest of the cars on the road. Tunnel? Avoid those bridges, won't even need an extra lane, because you're one less car on the road.