VDOT prominently advertised in various forms of media in advance of the rehab of I-95 through Richmond so that motorists would take I-295 during that project (there were even advert inserts at gas pumps in Fredericksburg.
VDOT signed I-95 ALT or DETOUR signs a number of years ago when the Emporia-to-NC debacle of pavement rehab was taking place. Motorists were directed to use US 301 and NC 48.
VDOT also has folded emergency I-95 detour signs in place from Richmond to Washington along US 1, though I've seen some of them down when there was no problems ongoing.
I had a recent experience with ALT/DETOUR interstate postings. SCDOT is doing something major to the I-95 SB bridge over the Great Pee Dee River. There were VMS signs starting in Dillon advising following a detour route that started at SC 38. When I got to SC 38, the queue to the bridge had already reached it (6 miles away). I took the detour (SC 38 and US 301) and not many others did so, despite the ample warnings in place by SCDOT.
My personal opinion is that this US 301 to MD suggestion will either not be used by very many or if it is will be terrible for those using it once they reach Dahlgren. VDOT should also at least on their website tout CBBT as an alternative to I-95 traffic heading to the Wilmington DE or further north area.