Seriously, at least in France the big success story in my book has been the use of heavy-duty buses to expand transit networks. You just gotta take over existing lanes, and you make your main bus lanes have buses every 5 minutes or so. It's not ideal but it exists and works.

Highly recommend as an alternative to wishing for metro lines.

They did the same thing in Bogota, Colombia. Massive project but when I was there it seemed to have paid off very well.

It is adaptive! You can change the routes based on demand or even time of day.

They kinda did that in Brissie!