Hi, these behaviours don't necessarily mean your dog is feeling aggression. Leads to the dog can be an invisible obstacle and these behaviours are an expression of your dog experiencing very intense emotions, and they’re trying to cope with those overwhelming feelings by doing things that make them feel better. More often than not, they learn that barking and lunging works for them! It gets them what they want. But what do they want?
You mentioned that your dog has played with others then barked on a lead on the street. Have you considered approaching the owner at the park and asking for 5 minutes of interaction on the lead? You dog may simply want to play and by associating positivity on a lead may reduce the need for barking?
Are there other triggers? Such as distance to another dog on a lead? If you notice a repeated association then trial crossing the road/ changing path to completely remove your dog from the situation before it arises.