Its Switzerland, so I'd assume the mountains and snow play a big part in increasing the cost of surface road building and snow clearing, making tunnels more attractive.
Most of the area of the map does not get intense snow.
It is in the northern part of Switzerland, the very lowlands of the alps. In my two winters here there would be a few weeks of mild snow, at the very most in this area (and the first winter here had a 1 in 10 year blizzard).
And there are some topographical changes, but nothing very steep. There are 100 KPH highways all throughout this area, and more convincingly, fairly high-speed rail too.
The problem is more that the Swiss Plateau (where most of these tunnels would be built) is very densely populated. There's just not enough room for a whole new road network to be built on the surface.
Yeah, I think this might have been one of the reasons why no one created an initiative to stop this. If instead they proposed a surface railway a few communities might have objected.
