You should check out the ProtonScatter add on, that's what I used to place trees in our game. Granted I was pretty lazy with it so the results aren't super great. But you can place boxes where your scatter items will spawn, and boxes where they aren't allowed to spawn, so you could easily block them from spawning in the road. And you can set it up so that they are randomly placed, with random orientation, and even random scale within a range so they are all slightly different heights. Super helpful for placing scatter, I would have gone crazy if we had to hand place everything lol