Our 3 year old Mickey is a very sensitive dog. Sensitive to everyones emotions and to his surroundings. He is scared of thunder, fireworks, etc. That is normally quite controllable as we do not ever bring him near fireworks and during thunderstorms he goes downstairs into his crate (on his own). It is never anything too severe and he recovers quickly. 

A few months ago we were at a dog park when a sudden surprising thunderstorm and downpour hit within minutes. We got caught outside in it but left quickly  The damage however had been done. We went back the next day and he remained stressed in this area...tail between legs, at our heels constantly, unable to focus, wont take treats, etc. We stayed away from this area for about a week and then went back and all was good - it seems he had forgotten it. We then went on vacation for the summer and he had a great time. When we returned we went back and all is still good at this park!

Our new problem developed about 2 weeks ago. We were going for a walk right outside our house which is in a city, lots of traffic, construction, etc. This has never bothered him before. Out of the blue he began experiencing the same symptoms as he does during a thunderstorm or fireworks. Cars driving by, big trucks, etc. This has NEVER bothered him in the 2 and a half years he has been with us. Everytime we go outside he is now freaking out. We unfortunetly do not have the option to avoid this as it where he needs to go every single day. It gets worse as we approach busy streets or when loud noises occur but we are not able to go around this. Nothing has changed in our routine besides a thundershirt we didnt seem to make a difference on or off. We do manage to get outside the city on weekends and take him offleash in fun areas where he is totally fine. But we do need to correct this anxiety in the city as this is where we live and where he has to live and do most of his walking. It is to the point where he doesnt want to go outside, freaks out on the walk (which we now have to cut short) and the second we walk inside his tail pops up and he feels fantastic! 

Any ideas or suggestion?

Sorry for the long post, just thought I should explain a bit of background. :)