155.475 is the nationwide police frequency. NCSHP lists the freq. on ch#5 of their high band system. 453.700 is listed as a mutual aid frequency by 20 counties in N.C.
I can remember working down east in NC and having 155.250 as a VHF mutual aid for that area of the state. 154.875 covers the west and 155.250 covers the east.