What are they building in the woods along Braddock Road across from the Newgate neighborhood? I have noticed a lot of construction vehicles back there, and can see they are installing a bridge over the creek back in the woods. Are they turning the area into a park/trail?

It's a new "agency" facility. I'd say more, but...

It is the new office building for Fairfax Underground. It is so good to see that they are finally expanding.

Section 8 housing

In other words, none of y'all have any idea what it is...

I have heard they are indeed putting up a bridge and adding to the path. I'm hoping they make the path go all the way to Walney Pond.

It's part of the county-wide stream valley restoration project.

http://www.fairfaxcounty.gov/dpwes/construction/bids/afb_rockyrun.pdf

See page 9 here:
http://www.fairfaxcounty.gov/dpwes/watersheds/publications/br/appendix_c_part4.pdf