# Transportation Economics/Supply chains

A supply chain can be better thought of as a web—an interconnected chain of "nodes," in this case, suppliers. In short, a supply chain is a network of distributors (of materials or finished products) and transporters (again, of materials or finished products). A supply chain may be simple or complex, depending on the situation and the industry.
Now for a general question about networks: what is the difference between economic analysis of networks and network analysis of the economy? Economic analysis of networks is required to understand and predict the deployment of advanced technologies, such as road pricing, and how those technologies interact and depend on each other. The central idea of a network is links that reinforce each other. These links can be physical (threads, wires, beams, highways, rails, pipes) or socioeconomic (kinship, social, or exchange relationships). The market, on the other hand, is a place where exchange of goods takes place. An economic network may be comprised of multiple markets. A market may sell the right to use, or the ownership of, physical networks.

## Network Model of the Economy

Levinson, David and Kevin Krizek (2008) Planning for Place and Plexus: Metropolitan Land Use and Transport. Routledge

### Nomenclature

Legend:
* Agent: stage s, market m, firm number n
* Open or hatched circles indicate production/consumption agent nodes
* Filled circles indicate market or exchange nodes
* Lines indicate links connection markets and agents
There are three main elements:
* the site of production/consumption (material transformation),
* the site of exchange (ownership transformation),
* and the connection between the two (spatio-temporal transformation).
While each of these elements is modeled as a link or node, it should be remembered that each can be expanded to form a subnetwork of itself if there is a desire to increase the detail or resolution of the analysis. A production/consumption agent in an economic network has both suppliers and customers, and can be modeled as an “agent node” on a network. Because production and consumption are two sides of the same coin, they are referred to together, any process consumes inputs to produce outputs. The “exchange nodes” are defined by the convergence of “connection links,” and are analogous to markets.

### Linking Economy with Transportation

Clearly this situation is idealized. Some firms may have different degrees of vertical integration, that is they may internalize what is represented here as an input market or the output market. However, this figure does reflect that a production process may have economies of scope, so that a single firm produces for more than one output market, as is shown in Figure 1 between Stage 2 and Stage 3. In the illustration, there are three stages (1,2,3 from left to right) several markets in each stage (for instance a market for capital and a market for labor) and multiple firms in each market. Extending the chain far enough to the left and to the right, and incorporating enough of the economy, the markets connect with each other again, as the ultimate final consuming agent is the individual consuming goods and an ultimate input agent is an individual producing labor.
To compare with a conventional transportation network, a roadway link is a composite of the “agent node” and the “connection link”. For each link on a highway, there is only one input market and one output market, each identified with a single node (an intersection), which makes the graphic representation and analysis simpler as the agent nodes are unnecessary because the transformation is only spatial, not material. While there is “conservation of flow” in the network, flows can be one way, the link moves traffic in one direction with nothing in return. As part of a larger system, the link (more precisely, an agent: Department of Transportation, Turnpike Authority, private firm acting on behalf of the link) receives revenue from government or users, which is used to maintain the link.

### Payment

In one sense, the link is selling the right to be traveled on and is paid by users or government for this right.
If it is not paid, it deteriorates over time (the payment comes from the link’s own capital stock which is dissipated). The more generalized version of a graphed economy subsumes the transportation network as a special case. The use of this framework serves to incorporate, at least conceptually, financing in the standard highway network analysis, and thereby allows us to identify some pertinent issues.
In particular if we identify links with firms, the issue of payment becomes clear. In order to operate, the link must be subsidized by government, be paid for directly by users, or allow its capital stock to deteriorate. Direct payment from users equal to the marginal cost is clearly more efficient, it does not entail the social loss described in section 2 due to overuse and subsidy, and does not impose deadweight losses inherent in certain taxing structures. Imposing road pricing is a natural conclusion to these problems.

### Snapshot

Figure 1 is a snapshot, it describes the processes and relationships at a given point or window of time. Over a long period of time, links and nodes are added and deleted as the economy grows and contracts, markets change, and innovation occurs in response to entrepreneurship and invention. The purpose of this analysis is to provide a tool to examine how networks and relationships in general do happen. We might extend the standard network flow idea of the least cost path to the process. Then “final” customers on the right side purchase a bundle of goods which provides the highest utility or lowest cost, profit seeking production/consumption agents in the middle will act as efficient customers for the initial producers on the left, and efficient producers/transformers in their own right. The network will generate welfare maximizing flows under the usual strong assumptions from microeconomics: well defined property rights and the absence of externalities (or when there is internalization of externalities), the presence of competitive links throughout, convex cost functions, etc. The interesting cases are in the absence of one or more of those conditions. Furthermore, the degree to which the network itself is efficient is another, much more complex (and important) question.

## Supply Chains

Ram Ganeshan, Terry P. Harrison, An Introduction to Supply Chain Management
"A supply chain is a network of facilities and distribution options that performs the functions of procurement of materials, transformation of these materials into intermediate and finished products, and the distribution of these finished products to customers."
"Supply chains exist in both service and manufacturing organizations, although the complexity of the chain may vary greatly from industry to industry and firm to firm."

### Single-Product Chain

"To the right is an example of a very simple supply chain for a single product, where raw material is procured from vendors, transformed into finished goods in a single step, and then transported to distribution centers, and ultimately, customers. Realistic supply chains have multiple end products with shared components, facilities and capacities. The flow of materials is not always along an arborescent network, various modes of transportation may be considered, and the bill of materials for the end items may be both deep and large."

### Supply Chain Decisions

"We classify the decisions for supply chain management into two broad categories -- strategic and operational."
* Location Decisions
* Production Decisions
* Inventory Decisions
* Transportation Decisions

## Modeling Approaches

Network Design methods, for the most part, provide normative models for the more strategic decisions. Optimization of system. Inventory Control methods, on the other hand, give guiding policies for the operational decisions. These models typically assume a "single site" (i.e., ignore the network) and add supply chain characteristics to it, such as explicitly considering the site's relation to the others in the network. These derive from Inventory Control optimization Simulation methods are used to evaluate the effectiveness of a pre-specified policy rather than develop new ones. It is the traditional question of "What If?" versus "What's Best?".

## Bullwhip effect

    See also: Bullwhip effect
Because customer demand is rarely perfectly stable, businesses must forecast demand to properly position inventory and other resources. Forecasts are based on statistics, and they are rarely perfectly accurate. Because forecast errors are a given, companies often carry extra goods (an inventory buffer) called "safety stock" to account for and take advantage of possible unpredicted increases in demand. Moving up the supply chain from end-consumer to raw materials supplier, each supply chain participant has greater observed variation in demand and thus greater need for safety stock. In periods of rising demand, down-stream participants increase orders. In periods of falling demand, orders fall or stop to reduce inventory. The effect is that variations are amplified as one moves "upstream" in the supply chain (further from the customer).
The Beer Distribution Game, developed by the MIT Sloan School of Management in the 1960s, is an excellent simulation of the sequence of events. In the game, several teams of at least four players are in competition to meet demand for beer casings, however, only one player has knowledge of actual customer demand. Verbal communication between team members is prohibited, resulting in both massive backlogs and massive inventory buildups—the bullwhip effect, as well as frantic players.

## Freight Logistics

Freight Logistics is the process of planning, implementing and controlling the efficient, effective flow and storage of raw materials, in-process inventory, finished goods, services and related information from point of origin to point of consumption to meet customer demands.
This management is increasingly important as producers move from a inventory based system (push) to a just-in-time system (pull). This is enabled by (and demands) reliable transportation and information technology. The process is multi-modal or inter-modal, that is, it uses multiple modes of transportation. Most products are loaded and unloaded multiple times at various stages within the logistics cycle.
| | Value (%) | Volume (%) | $/lb | Avg Length (mi) |
| Trucking | 72.6 | 52.6 | $0.35 | 416 |
| Railroads, | 4.0 | 12.7 | $0.08 | 794 |
| Maritime, | 3.9 | 17.2 | $0.06 | 2300 |
| Intermodal | 10.4 | 1.7 | $1.61 | |
| Airplanes, | 2.4 | 0.02 | $26.77 | 1325 |
| Pipelines, | 2.8 | 10.8 | $0.09 | 825 crude, 375 other |
| Other | 3.9 | 5.0 | $0.20 | |
Freight tons per capita has been increasing slowly (about 0.1% per year), but freight ton-miles has been increasing at more than 1% per year. In other words, freight being shipped farther and farther.

### Railroads

Railroads move low value commodities long distances slowly (e.g. coals, chemicals, farm products), as well as large items that can't be easily or efficiently moved by truck (e.g. cars and large machinery).
Class I—major railroads
* Western (east west) Burlington Northern/Santa Fe, Union Pacific,
* Eastern (east west) CSX, Norfolk Southern,
* Central (north south) Chicago and Northwestern, Illinois Central, Kansas City Southern, Grand Trunk Western (Canadian National), and Soo Line (Canadian Pacific).
Class II—regional and short line railroads

### Trucks

Trucks move higher value products short distances rapidly.
Truckload—one shipment, one truck
Less than Truckload (LTL)—multiple shippers use same truck.
Some owned by manufacturers, some by private trucking firms, some by publicly held (stock market) trucking firms.
Small trucks are often used as private vehicles, so truck statistics need to be considered with care. Almost 60,000,000 trucks in United States.

### Low Cost Envelope

Which mode is selected depends on which mode has the lowest cost, typically this can be illustrated with the low cost envelope: