US 6 in CT w/ I-84: Joins it from Exit 4-8, leaves, rejoins from Exit 10-15, leaves, rejoins again from Exit 38-60.
US 1 w/ I-95: Joins to cross the GWB, rejoins to cross the Baldwin Bridge in CT, rejoins to cross the Gold Star Bridge in CT, rejoins from Exit 27-29 in RI, rejoins as a wrong way concurrency from Dedham to Canton, MA
US 6 and US 202: Join from the west end of the Bear Mountain Bridge to downtown Peekskill, rejoin from Brewster to I-84 Exit 7 in CT (including quadplex with I-84 and US 7)
US 6 and US 44: Joined in I-84 to cross the Bulkeley Bridge, rejoin from I-84 Exit 60 to Bolton Notch, rejoin again along I-195 from Providence into East Providence.
US 7 and US 202: Joined as part of the quadplex above, then rejoined from the end of the Brookfield Bypass to downtown New Milford.
If you count MA 3 and US 3 as one route, it joins I-93 from the Braintree split to Downtown Boston, then rejoins along the Franconia Notch Parkway in NH