userform one combobox dependent on another

Do not use additem to populate a combobox or listbox

This will be sufficient:

Private Sub cboRoadway_AfterUpdate()
    cbostreet.list = sheets("Data").cells(1,1).offset(,cborailway.listindex+1).specialcells(2).value
End Sub

I suppose
roadways in column A
streets of first roadway in column B
streets of second roadway in column C, etc.