I can't tell you the time because we haven't gone that way yet, but this is exactly what we plan to do in November. We are staying at a Comfort Inn in Hillsville VA on the way down. When I plug the RI to FL route into
AAA, all the red flags for traffic come up due to 95. We do a lot of driving-- RI to IL to MO each summer, and I know that I sometimes go off the main route, but it never makes a difference in time since we don't get caught in traffic. If you have AAA, go to their website and click on Travel in the top row. Then click on the Trip Tik travel planner. It has a new feature that allows you to map a route making your own highway choices-- it has a little icon you pick up and use to allow you to plan a route to your specs. It helped me get exact mileages for our trip 81 to 77 to 26 to 95. I wouldn't hesitate to go that way. Also, you can Google Earth the route and see that there are virtually no cities along Route 81. For us it is 1258 miles on a direct 95 trip. The other way is 1385 miles. Overall the trip is about 130 miles longer for us. I'll take a chance on assuming I could be slowed up for 2 hours in traffic if I go NYC, DC, Richmond, etc. Even if I'm not, the view of the Appalachians is worth the detour! Time NOT spent in traffic...Priceless.
Let me know what you choose to do and how you like it! I'm traveling with DH and 2 DDs (with their DVD suite in the back of my Yukon XL

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Heidi