I wonder whether any GPS can parse addresses like 123 W E St out in Shelton. Not to be confused with 123 E St SW in Auburn. As a deliverator before GPS was common, figuring out how to look stuff like this up in a Thomas Guide was pretty entertaining.

bellvue ave, bellvue court and bellvue place intersect in cap hill.

to answer the OP, those directionals are required to uniquely identify addresses in Seattle: http://en.wikipedia.org/wiki/Street_layout_of_Seattle#Direct...

note that they're prefixes for east-west streets, but suffixes for north-south avenues.

I've lost deliveries before when I've omitted the directional, even if the street #/street name was unique to the zip code.