I am living in an apartment which has a balcony right next to the small road. Even thought the road is quite small, cars are still driving there and it makes a lot of sound if the doors to the balcony are open.
The balcony has no solid vertical wall toward the road, but only iron bars every 20cm. Would that help if I would put on the ground a half of meter height plastic (or other material) board over the length of the whole balcony next to the iron bars?
I don't expect 50% of noise reduction but at least little bit would be good.
To illustrate my point, this is how it looks: