Roads do have a price, and it does increase with demand. What is the worth of 10 minutes of your time?

The problem is that you don't pay for the slowdown you cause to everyone else. You're offloading that cost, so you keep choosing to use the road well beyond the point where traffic should be increasing.

To make up for that, we can charge people at the entrance point. But charging people time is basically impossible, so money is used instead.

Therefore more roads => more cars => same trip times. I could see that people would make decisions to take jobs where they travel by car, or choose to live further away etc. with more tunnels. That could be a good thing or bad, but yes the demand will increase, because people will find new reasons to get about if there is more road to do it on. Let alone business use of roads.

Do you not see how you're arguing in favor of his/her point?