It is absolutely stupid to add more lines for a main road as long as the outflow from it can't handle it. Ten lanes of motorway makes no sense if the one outlet 90% of the cars want to take has one lane and nasty traffic lights at the next corner.
City planners should be forced to play Cities:Skylines. Lessons to be learned: a) Make public transport good and free, and b) Lane Maths.
Part of the problem with city planners is that much of their job is just alleviating car traffic. And if they were successful at doing (like making good public transport and walkable cities) they would have far less work, and be put out of a job.
That being said, I think they would realistically just start working on other city issues, but I think that's the mindset that keeps them building this kind of stuff.
I bet there's also a factor of that things are already going in this direction, and there's already more demand for driving, and it's far more difficult to go against the grain.
But when a road connects three urban areas with multiple suburbs in every direction, weird things happen. Most traffic horror isn't in road planning at all, it's in urban and suburban planning.
Why do 3 million people need to get from one side of LA to the other on a regular basis?
All good and well until you have a 3 or 4 trailer road train limited to 90kph with a poor little box truck stuck behind it wanting to do 110kph. Trucks should be allowed in the middle lane for overtaking each other.
If a train were to go along that whole motorway it would take up a fraction of the space, carry most if not all those people, and move them faster than this.