Each of the zip codes in the left column pairs with a zip code in the right column to form the endpoints of a US Route. (This is clued by the title, which refers to the song "Route 66".)

55025  49870  Rt. 8 
29907  24382  Rt. 21
34221  16504  Rt. 19
98201  49781  Rt. 2
33040  04743  Rt. 1
82190  60640  Rt. 14   
12061  03801  Rt. 4

Treat each route number as a letter to obtain the answer, HUSBAND.