Route 1 seems like a local-road to me with lots of traffic lights though.
I-95 works really well as long as its clear. But as soon as an emergency happens, the spillover traffic is too massive for Route 1 to ever hope to handle. An interstate-highway can't rely upon a traffic-light laden local road to handle the traffic from a 4-lane interstate.
EDIT: In the case of the 2017 eclipse, the traffic was so heavy that truckers started to pile up on the side of the roads (allegedly due to the laws stating that they could only drive for X hours at a time). Losing a few lanes slowed down traffic dramatically, causing even more truckers to just pull over due to legal requirements. I don't think the GPS / Waze ever recommended for us to leave I-95 during this time, so Rt. 1 was never a consideration.
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A 2-lane highway without traffic lights that runs parallel would help a lot. I don't know the lay of the land in Virginia (ideally such a road would be coordinated with local suburbs / local cities to lessen day-to-day traffic as well).
It looks that way on Google maps maybe, but as someone who grew up in Richmond it's a route nearly all Virginians take up to DC if there is any traffic on I95 and is a well known alternative route.
US Route 1 is already an interstate highway with 4+ lanes through the area you're talking about. Development was encouraged down the I95 corridor since its creation and the density that has resulted pretty much makes this unavoidable. There was a similar situation with the Woodrow Wilson Bridge on 495 outside of DC in 1998 when it was closed due to a jumper during afternoon rush hour, and the traffic jam lasted overnight despite there being alternate major routes in every direction. The problem is that the bridge carried more traffic than all of the alternate routes put together (I'm assuming based on my experience).
The former Jefferson Davis Highway (now Emancipation Highway) has never had the capacity to back-stop I-95. It can be used in emergencies, but only if one wants to get stuck in a slightly different place with an occasional soda machine within walking distance... A feature one stuck on that road may be able to take advantage of, given the speed one will be going.
And I don't imagine it would be much use in a sudden-onset winter storm, since it's right next to I-95; it's going to get blanketed about as fast as I-95 will, and most of it lacks enough shoulder for plows to get along it if it gets jammed with traffic.
US Route 1 basically parallels I-95 in most of VA. I was once detoured on it after a military HAZMAT incident. It’s slow going, but it works.