Transport network structure
Transport network structures are different combinations of routes and warehouses in logistics , especially in groupage and general cargo traffic . They arise from the arrangement of graph-theoretical nodes (sources and sinks of charges) and their connection via edges (network processes). Nodes thus represent storage locations and edge transports. A characterization can be carried out using the three criteria of gradation, density (number of depots connected in the network) and displacement (spatial distribution).
Plan-controlled distribution processes are considered out of date, but central distribution strategies require low transport costs and short transit times. Differences in transit times in “Europe with Borders” were and are still plausible and generally accepted today for Eastern European traffic. In Central Europe, however, only differences in distance are accepted.
Minimal networks
The simplest network structure is the minimum network, in which each node is directly connected to a maximum of two nodes. The advantages of this structure are the good utilization and the low number of means of transport that are required. However, the quality of the transport service, which becomes slow, time-consuming and error-prone due to frequent reloading processes at the nodes, is too low.
Direct traffic networks
A network form opposite to the minimal network arises from the direct (n: m) connection of each individual node with another. Complete direct transport networks are characterized by the fact that they enable the shortest connection between two nodes, so there are no detours. Since there is generally no direct transport from the source to the sink in general cargo transport, these nodes are often the collection depots of the forwarding agents. Direct transport networks are only suitable if the volume of general cargo is correspondingly high, or can be added to other partial lots, but there is also no excess. One example of a partial load network in the direct traffic network is the Part Load Alliance (PLA). While grid networks are generally equated with grid networks in the literature, a distinction is made between direct traffic networks and grid networks according to Hans-Werner Graf , whereby he refers very much to the gate networks that follow.
Gate and grid networks
Graf describes the grid network as a thinned-out direct traffic network between depots, in which traffic to or from less frequented routes is broken and there are no designated central transshipment points. On the one hand, such points of resolution and concentration can certainly be justified with the help of the load, but gate nodes are more often found in freight forwarding networks with the task of controlling flows between sub-networks. Such networks can often be observed within cooperation between small and medium-sized enterprises (SMEs). A country specialist has brought his sub-network (own branches, correspondents) into the cooperation. It should be emphasized, however, that gate nodes represent access points to sub-networks, i.e. foreign connections such as the Czech Republic in this example, do not represent gates, but classic direct connections.
Hub-spoke systems
Network structures with one or more main handling nodes are known as hub-and-spoke systems. In 1973 this structure, developed by Fred Smith as part of a seminar paper at Yale University, was introduced to the parcel service FedEx , which he founded . Due to the liberalization of the American air transport market at the end of the 1970s and the threat of competition with regional providers, the system was used by the major airlines to significantly increase the range of destinations and flight frequencies. The system found its way from being used in air traffic to general cargo traffic on the ground. The principle is based on the fact that consignments are consolidated at the collection depots and brought to a central transshipment point. So there is no longer any direct traffic between the individual nodes, but bundled transports to a central node. In this central point, the hub, all incoming shipments are sorted into targeted deliveries and then delivered back to the start-destination nodes. This structure got its name from the "star-shaped" approach of the edges to a central node, like the spokes of a wheel on the hub. The main advantages of such a system are (V1) the lower number of edges that are required to connect the same number of nodes, (V2) the higher utilization of the vehicles, (V3) the higher transport frequencies between the nodes and ( V4) in a high technical specialization in the hub. On the other hand, there is (N1) the high risk of infarction of the hub, (N2) the additional transport service and thus higher transport costs per shipment and (N3) the greater risk of transport damage or incorrect loading due to handling in the hub.
In Germany, such hub-spoke systems are used to cushion the excess volume and to serve low-volume relations. For example, 18% of the volume of the general cargo cooperation 24plus is served via the hub and the remaining 82% via direct transport. In the case of networked transport logistics (VTL), on the other hand, around 90% of the traffic is handled via the hub.
In addition to additional regional hubs, in which intra-regional traffic is dispatched, additional central, inter-regional hubs can also be introduced. Although the average distances are reduced by additional hubs, as there is no detour via the central hub, the average utilization also decreases. In land transport, the general cargo cooperation SystemAlliance operates a multi-hub system with the German central hub in Niederaula . However, especially with multi-hub systems, particular attention must be paid to whether there is actually a regional hub and not a distinct gate network.
Individual evidence
- ↑ Hans-Werner Graf, R. Jünemann (Ed.): Network structure planning: An approach to the optimization of transport networks. Dissertation 1999. Verlag Praxiswissen, Dortmund 2000, ISBN 3-932775-49-X .
literature
- H.-W. Graf, R. Jünemann (Ed.): Network structure planning: An approach to the optimization of transport networks . Practical knowledge, Dortmund 2000, ISBN 3-932775-49-X .