The concept of transport infrastructure capacity is complex. The nominal capacity of most transport terminals and infrastructure, is the traffic they can handle within a time frame and normal conditions in terms of reliability. It is jointly defined by static and dynamic considerations:
- Static capacity refers to the available land as bigger terminals or larger roads (more lanes) have conceptually more capacity. Static capacity cannot be easily changed without expanding the facility or the infrastructure, which tends to be capital intensive and requires additional land. In areas of limited land availability (or high land cost), this can be a complex proposition.
- Dynamic capacity relates to infrastructure, labor and technology, which can be improved upon. For instance, a more efficient terminal operation strategy can increase its physical throughput and consequently its capacity without resorting to additional land. The dynamic capacity of a road system can also be improved with a better synchronization of traffic lights. The intensity and density of utilization is improved with more efficient superstructure and management.
Dynamic capacity is a straightforward strategy to improve the efficiency and productivity of transport assets. However, at some point an optimal level dynamic capacity is achieved and nominal capacity can only be improved through additional static capacity (or demand reduction or modal shift).
Optimal nominal capacity cannot be effectively achieved particularly since a specific transport facility or infrastructure is linked with others, so that capacity improvements must be synchronized. For instance, a port terminal operating near optimum nominal capacity is facing serious congestion issues in the form of queuing at the terminal’s access points; ships may be queuing on the harbor side to access the terminal while trucks may be waiting at the gate to pick up or deliver containers. A similar situation applies to airports where the capacity of an airport is impacted by the capacity of other connected airports as well as its capacity to handle security procedures and baggage handling. Transportation infrastructure operating above 80% of nominal capacity usually start to encounter dynamic capacity issues.