>>-81 isn't anywhere near D.C. or Baltimore (it's mostly a mountain/rural interstate), and thus doesn't do anything to offload traffic from I-95.
I disagree. I'm looking at I-81 right now from the front desk of a hotel. On any given night, there are guests at the hotel coming from Maine, going to N. Carolina, etc... They do this to avoid traffic on I-95.
Having to deal with the constant construction on 81 is another matter entirely, though.