Tweets can now be embedded on the forum. Just paste the twitter URL into your post and it will render.
Your link to the detailed highway history of Oregon doesn't work, though. Here's the correct link:http://egov.oregon.gov/ODOT/HWY/GEOMETRONICS/ROW_Eng/HistoryHighwaysOregon/HSHO.pdf
Here's Iowa: http://www.iowadot.gov/maps//msp/historical/transmaps.htm
The Virginia link seems to have died. Anyone have a new link?
I don't know if there's anything useful here that's not on the other maps, but Oklahoma also has traffic count maps going back to 1937: http://www.okladot.state.ok.us/aadtcnt/Default.aspx?list=staticMaps