How do you handle interplant freight costs?

My company's interplant freight costs have ballooned in recent years, due in part to inefficient planning. About half of the cost is semi-finished products shipped to a different plant for completion. Others are raw materials resupplied to plants in need. The available data does not split the sources - truckloads are often mixed between the two. My question is.. 1. How do other companies treat this cost from an accounting perspective? Especially where segregation is not possible, is this included in raw material costs? As with inbound supplier freight.. 2. From a cost controlling perspective, how do other companies segregate this cost (i.e. separate cost center?) to ensure visibility and proper accountability, and to keep this separate from pure inbound supplier or outbound customer freight costs. Any advise or insight appreciated.