Hey,
you've got 'track' defined on the shipments collection so it would be:
track_shipments_path(order_id)
But seeing as the URL you quoted is for a shipments *member* (/orders/ 333/shipments/111;track), you probably want this:
orders.resources :shipments, :member => {:track => :get}
in which case, the helper would be (as you expected)
track_shipment_path(order_id, id)
HTH, Trevor