Right now tunnel boring machines are expensive and we only use them for a few projects. If they were cheaper we'd have a lot more of them and use them for many more roads.
I've long wanted tunnels for lightweight freight transportation (see my blog post from 2005) but I'd also like tunnels for infrastructure in general — electricity, gas, water, gray water, cable tv, telephone land line, fiber optic internet, mail delivery, trash collection, etc. It's a shame that we have to dig up roads to install or fix any of these. It's a shame that I can't get gray water for my yard and am using drinking water to water my flowers. It's a shame that fiber optic internet access is so expensive to install. It's a shame that we have to see ugly power/telephone/cable lines everywhere. Also, a lot of this stuff would be better out of the weather.
Cheap tunnels would change a lot of things! I'm hoping Elon Musk will make this happen!