Bottlenecks impose delays and restrictions in the normal flow of transportation. There are three major types of bottlenecks:
- Infrastructure bottlenecks. Infrastructure bottlenecks can be the outcome of chronic or temporary conditions. Climate change can be a factor altering conditions that could damage transport infrastructure and shorten its useful life. Physical restrictions can form bottlenecks as traffic expands, such as a bridge or a port. Under-investment in infrastructure can produce chronic bottlenecks when rapid economic growth takes place, implying that the capacity is insufficient to keep up with the demand. Temporary bottlenecks can be caused by natural or market forces. Weather disruptions, such as a storm, are among the most prominent, as well as construction, accidents and labor conflicts (strikes). These events are usually expected, but cannot be predicted. A surge in demand can also create a bottleneck as infrastructures are designed to convey a constant level of service. Dis-investment, often through the lack of maintenance, can cause temporary bottlenecks.
- Regulatory bottlenecks. Regulations that delay goods movements for security or safety inspections create bottlenecks as a direct consequence. If international movements are concerned, custom procedures for passengers and freight are a common source of delays. Even if the intention is not to convey delays, regulations inevitably cause delays and disruptions. There is also corruption, imposing uncertainty and a burden on transport operations. Three sources of bottlenecks created by the indirect effects of regulation are cabotage restrictions, competition policies, and fiscal policies. Cabotage restrictions prevent foreign carriers from carrying freight within a country; their capacity is thus not available. Competition policies can create bottlenecks either by supporting a monopoly where the operator engages in rent-seeking strategies or by complete deregulation where many carriers will compete with the similar transport segments. Fiscal policies can deter investments through taxation and create bottlenecks.
- Operational bottlenecks. Relate to specific tasks and procedures in the management of transportation modes and terminals that trigger bottlenecks. From a capacity perspective, the availability of equipment and vehicles can create bottlenecks as the necessary conveyances may not be where their capacity is needed. Further, labor availability, such as work shifts, may impose time-dependent capacity shortages. From an efficiency perspective, the productivity of modes and terminals can vary along the transport chain and can create bottlenecks. This is particularly the case when tasks and sequences along a transport chain are not properly coordinated, or when labor skills are lacking, which can create bottlenecks. Different information exchange protocols can create delays in information processing and therefore delays in shipments (or transshipment).