The global rail network, which is mostly a collection of unlinked national rail systems, involves three main types of rail lines:
- Penetration lines. Their main purpose is to link a port city with its hinterland, particularly to access natural resources such as minerals, agricultural products, and wood products. The purpose of a penetration line is to convey large amounts of materials in a manner that would be prohibitive for road transport. It also represented one of the initial stages of rail development, notably in the United States, which later became regional networks linked by transcontinental lines. Today, penetration lines are mainly found in developing countries (Africa and Latin America) and were partially the result of the colonial era. Such areas have several gauges and limited cross-border connectivity and thus offer limited competitiveness with trucking. For instance, 80% of South Africa’s coal output comes from the Mpumalanga region, which is about 590 km from the port of Richards Bay. Large coal trains are used to carry the coal from the mines to the port. Penetration lines are also found in resource-intensive advanced economies such as Australia and Canada. Transporting freight is the dominant function of this type of network, although passenger traffic can be significant since penetration lines can also be servicing an urban system.
- Regional networks. They represent well-developed regional networks servicing high-density population areas of developed countries, intending to support the massive shipment of freight and passengers. This network type initially started as penetration lines or interconnected city pairs and evolved to form a lattice. Regions with the highest rail density are Western Europe, the Northeastern part of North America, Coastal China, and Japan.
- Transcontinental lines. These lines were mainly established to improve territorial accessibility and for the setting of national sovereignty. The most relevant examples are in the United States, Canada, Russia, and Australia, which have built rail systems of this scale, such as between New York and Los Angeles, across Eurasia (between Dalian and Moscow), across Southern Australia (Perth and Adelaide) or across South America (Buenos Aires and Valparaiso). More recently, transcontinental rail lines have seen a renewal in interest by their capability to attenuate the discontinuity of maritime transportation by transporting containers such as over the North American Landbridge and the Eurasian Landbridge. They are a chain in the global intermodal transport system.