Ex in-laws used to live between Las Cruces and Truth or Consequences. Right near Elephant Butte Lake. I've been to most of the places you're describing. Check out the Hot Springs in T or C👍
Look on google maps using earth view, zoom in enough and you can find Three Notch Trail, that's the bike path through Mechanicsville. That's the old railroad right of way. It pretty much paralells Rt.5 down to the Mechanicsville Elementary School then veers westerly. Then just before crossing...
Consider how bad traffic is on Southbound Rt.4 on any given afternoon/evening. Now add to this everyone from DC, Northern Virginia and PG County wanting to go to the Eastern Shore/OC. You'd need to add another 2 lanes both North and South and I don't see that happening in Calvert. Next go to...