Very well polished game! I had a few notes (sorry if others have said the same already):
- It would be nice to see the score as the game goes, so the player has some way of knowing how they are doing.
- I noticed a bit of lag during the traffic phase. I was playing on WebGL, and I saw it starting probably around 30 houses, for reference.
- A straight line tool would make road phase a lot quicker/more comfortable to the player.
- I found the rules about road-placing somewhat confusing. I didn't understand why I couldn't have roads which curved around houses (though I'm sure there is a good reason I shouldn't be allowed to do this).
- I think the game might be more intense if everything was happening at the same time, rather than in phases -- so the player has to react with reflexes and can't spend as much time planning everything.
- Strategy-wise, different kinds of roads/buildings might be helpful to giving the player more choices to make; for example, a highway-type road, which can't connect to buildings but doubles car speed, or a high-density building (like an apartment) which will have twice as many cars in/out of it. Choices/info like this will enable players to develop more complex strategies, if that is the route you wish to go.
Overall very well done! I noticed you are considering a full release -- good luck, I'm sure it will be great!