A train would solve that, but I understand that this isn't a good solution for all cities. As often said we have to change transportation happiness, and so we will
Your observation is right, <30% might start a demonstration, and if happiness isn't fixed they will start a riot which can only be stopped by SWAT-teams.
I've got 3 demonstrations in a row! First one was because of enviroment and turned into a riot and they've burned down several buildings. Second one was because of fire brigade. I've sent police and it've helped. Third one was because of enviroment again and turned into a huge riot.
Then i paused the game, removed buildings with lowest enviroment rating, restored all burned buildings (they somehow burned police depot ). Now only polluted land remain. I've built some parks on it, so just waiting what will happen next.
My apologies, I'm new to the game in general as well to beta testing, but since the riots started, I'm having no fun playing the game.
I had just started a brand new city. I had one block each of res., comm., and ind. I had a small fire station, police department, doctor, a small school, and a gas power plant with a couple small parks and they rooted for clean air. Once that riot torched a portion of town and was finally quieted, they rooted for free time.....a brand new city.
Maybe if when a demonstration begins a teaching tool pops up and explains how to fix the situation, or maybe the option to turn riots off altogether, or maybe only have riots in higher levels of game play.