Given the volume of traffic that goes between 29 South and 66 East at the Gainesville interchange, I disagree with the need for a 3rd lane on 29 underneath 66...especially southbound 29. You'd have to end that lane before the ramps from 66 merge or else you'd be creating an untenable merging/weaving situation between 66 and 55.
Wasn't there at some point a proposal to move the U.S. 29 designation off of Lee Highway and onto I-66 from Gainesville (I-66 Exit 43) to Centreville (I-66 Exit 52) to reduce traffic through the Manassas Battlefield (including the signalized intersection at VA-234) and then downgrade former U.S. 29 to a secondary system road?
Under such a scheme, U.S. 29 southbound would follow the cloverleaf ramp onto westbound I-66 at Centreville.
I have not heard more about it in many years.
Most of what I see is 2013 or earlier - looks like they want to build a 29 bypass around the north of the battlefield to connect with the relocated VA 234:
http://www.virginiadot.org/projects/resources/NorthernVirginia/N-S_CIM_Presentation.pd
BiCounty (and before that, TriCounty) Parkway. Have not heard much about any of that of late.
IIRC, there was a a lot of NIMBY opposition to these projects.
What I was referring to was much simpler - just a change in signage, but no added capacity.
Would a change in signage really deter that many people from using US-29 through the battlefield especially if a majority of those people are frequent commuters and know that the roadway, whatever it would called, still connects back to I-66? Could only see this happening if US-29 was somehow made discontinuous through the battlefield which after the competition of the I-66 HOT lanes may be made possible who knows. At least there would be an alternative East/West route nearby. VA-234 on the other hand, a north/south connection between Prince William and Loudoun, Virginia's #2 and soon to be #3 most populated localities, not so much. With of the recent growth in South Riding, calling VA-28 and US-15 alternative routes is pushing it. Thus its interesting to me how even with hardly any intersections or exits, the bi county parkway is controversial enough to be off of PWC's thoroughfare plan while the east/west part of the battlefield bypass is on it even though it would theoretically never connect back to US-29 and imo be pretty useless.
Speaking of the thoroughfare plan and battlefield bypass, an interesting item on there is the idea of southern battlefield bypass in which a four lane road would branch off of US-29 at Pageland road, follow Pageland road south next to existing I-66, extend past Groveton road, pick up at the existing Battlefield Parkway in the vicinity of Exit 47 (BUS-234), follow Vandor Lane, and then somehow connect back to US-29 near its intersection with Bull Run Post Office road.
In terms of likelihood of every being completed, I'd put both the northern and southern battlefield bypass as being pretty low chance due to the likelihood of it triggering a compensation event. VDOT also likely wouldn't want to make improvements to a road parallel to roadway in which will soon have around $3 billion worth of improvements. The bi county parkway, while currently dead is actually imo the most likely of the three if Western Prince William County were to ever go democrat. However, the time window for that is quickly closing as that project gets ever more expensive with every passing year.
https://www.pwcgov.org/government/dept/dot/Documents/Thoroughfare%20Plan%20April%202016.pdf