I live in Seattle zone8 if it makes a difference

Which kind of arborvitae? 'Smaragd' (Emerald)?

By the way noise is going to come right through the hedge, whatever you do. If you want noise reduction, you're going to have to put in a high concrete wall. Like along parts of the freeway.

yes emerald.

as long as they don't start dying in few years for being planted so close im ok with it. too much work to replant them

Close spacing will just result in them not being as big and full many years later, when the crowding starts to kick in. In the meantime your desire for a solid screen will be the determinant priority. And maybe you aren't going to be living there for decades anyway.

haha. as long as I get 15 years out of these ill be alright.

I think it will not make much difference, except that it cost you more to put them closer.

how large were the transplants??

isnt your whole point.. goal.. that they grow together???? ... if so ... then space them so they grow together ...

when allowed to do this themselves.. imo .. its not a problem ... if you were to jam 2 huge plants next to each other.. it still wouldnt be that big a problem ... but you might get some uglies as they grow together.. and shade out foliage that was previously in full sun.. but even that would go away ...

ken