Note: g/cc: grams per cubic centimeter.
Mobility refers to the ease with which a passenger or a freight unit can move across a transportation system. High mobility requires limited effort, while low mobility is related to complexity and high costs. Passenger mobility has constant requirements (unless involving people with disabilities), with parameters related to tolerance to acceleration and deceleration, basic comfort, air pressure, and ambient temperature (for air transport). For freight, mobility is cargo-dependent, with some commodities having limited storage requirements but being heavy to carry. There are four major factors influencing mobility:
- Weight. A simple indicator of the amount of energy that must be spent to carry the cargo. Heavy cargo requires more energy to transport, as well as heavier modes of transport and equipment to handle it. Commodities such as coal, grain, and petroleum have a high density (weight-to-volume ratio). Containers can carry cargo loads of 15 to 20 tons each, irrespective of the nature of the cargo.
- Storage. The complexity related to holding the cargo in inventory before it can be used. This can range from simple piling to complex temperature-controlled warehousing. Commodities tend to have simple storage requirements, whereas retail goods require handling in distribution centers to ensure rapid market delivery. At the end of the spectrum, many food and pharmaceutical products require complex storage and handling procedures.
- Fragility. The ease with which the cargo can be damaged during transport. Ores tend to have limited requirements since they do not degrade during handling, and similar considerations apply to petroleum, albeit with the added risk of flammability. Fragile cargoes require additional handling and storage procedures since they will lose their market value if damaged.
- Perishable. Some cargo degrades after being harvested or manufactured. After a specific duration, their commercial value declines or becomes negligible. Because of time constraints, perishable cargo has much lower mobility than cargo that does not degrade over time.
All these factors must be considered when transporting cargo as they influence the transport mode to be used and its commercial potential.