Three-Digit Roads That Are Longer Than Their Parent

[PHLBOS]

Why isn't MA 3 a part of US 3? It makes zero sense.

Such has been discussed in past threads.  The likely thinking/rationale (or lack thereof) may be due to the then-MassDPW not wanting an odd US route crossing east of US 1 or not interested in or not applying for such (prior to 1971, US 1 & Route 3 crossed into Boston from Cambridge via the B.U. Bridge). 

Yes, I'm aware that such occurs in other locations (examples: US 9, 13 & 17) in other states but nonetheless that could've been the thinking.

[NE2]

The 1926 plan had 6 south of 20. Might have been interesting if Massachusetts requested that 20 go southeast from Boston.

[JCinSummerfield]

Where does US-127 fit in this discussion?

[GaryV]

Where does US-127 fit in this discussion?

27's nearly twice as long as 127, even after 27 was truncated at Ft. Wayne and 127 took over the northern portion.