Steve - those of us who live near "congested areas" (like just about all cities), might chuckle at your "less traffic" comment!
Regarding the speed change warnings, I'd guess it's so law enforcement can say "you can't say we didn't warn you" if they pull you over for disregarding the changes. Those "50 mph ahead" or "reduce speed ahead" type warning signs are certainly all over New England (Connecticut, Massachusetts, Rhode Island, etc.)
Just my two penn'orth.
Tom