Hi all,
This is from a newer Townhome. I have never seen this kind of a flooring system before, have you? Normally in a newer house you see TJI Engineered joists. This house used these 2x4’s that kind of look like a roof rafter design. New one on me. Ever see these?
fairly common—big in the 70’s
Floor trusses are fairly common here (since the late seventies)
Still see them on new construction.
They really are a dream from the standpoint that they make the installation of the mechanicals very easy. They add quite a bit to the overall height of the house, though, when compared with traditional flooring systems. I still see them in new builds, but they’re mostly employed by builders who were fetched up in the trade during the 70’s.
Typically, there is more flex than I like in this floor system.
Dishes rattle in the china cabinet when walking across the floor.
I had a house built in 1979 that you could feel when our 10 pound Terry-Poo walked within 10ft. of you if you had your feet on the floor. It took some getting use to but the dishes didn’t rattle and the decorations on the wall didn’t move unless you didn calistetics in the middle of the span.
Review this Marc.
http://www.artruss.com/faqfloor.htm
http://www.toolbase.org/Technology-Inventory/Whole-House-Systems/trimmable-open-web-floor-truss
http://www.alpeng.com/Floor_Truss_Systems.html
Hope this helps.
Marcel 
See them from time to time.
IN GA NEERED flooring truss. Depends on the builder and subdivision. Lots around Denver in Townhomes mostly. And Mark is correct, GREAT for Mechanical routing.
As always, Thank You to those of you who post your answers! I continue to learn a tremendous amount from here because of you guys! 
As I learn more of the things I am not too familiar on, in turn I can help others! Thanks Gang