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Improving port congestion with time slot management for ship arrivals and departures

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Improving port congestion with time slot management for ship arrivals and departures

Peter Sand

by Mikael Lind, Research Institutes of Sweden (RISE) and Chalmers University of Technology,
Wolfgang Lehmacher, Anchor Group, Jan Hoffmann, UNCTAD, Lars Jensen, Vespucci Maritime,
Theo Notteboom, Ghent University and Antwerp Maritime Academy,
Torbjörn Rydbergh, Marine Benchmark, Peter Sand, BIMCO, Sandra Haraldson, RISE
Rachael White, Next Level Information & Cool Logistics, Hanane Becha, UN/CEFACT,
Patrik Berglund, Xeneta


Port infrastructures are finite resources that, when used at their limits, become easily disrupted. Recently, at the United States (US) West Coast ports of Long Beach, Los Angeles and Oakland, vessel waiting times reached extraordinary levels, with some of the largest ships waiting nearly three weeks to get a berth (figure 1).

Figure 1: Average waiting times (days) in 4 weeks periods for 451 container ships that made 2400 port calls to Port of Oakland (1222 calls) and Port of Long Beach (1178 calls) during the period 1st of January 2020 to 13th of June 2021. Still is defined as 0 to 1 knots, and manoeuvring between 1 and 6 knots. The waiting time between 0 and 6 knots is aggregated with a maximum distance to destination of 125 nm.

Globally, congestion in capacity-constrained ports will continue to occur. The disruption in the container port system in southern China, like in the U.S. West Coast ports, is another recent example. Due to the fundamental nature of global maritime trade, congestion travels across intercontinental supply chains, where for example the congestion on the U.S. West Coast will be relieved by the emerging congestion at South China ports, but will bounce back to the U.S. when the Chinese ports are operating at full capacity again. Record high freight rates reflect the current situation in the maritime sector.

This is a call for an expansion of the Just-in Time (JIT) arrival approach to incorporate a slot management concept that includes a dynamic view and management of JIT arrivals and departures.

How ships are behaving at maritime chokepoints

During the congestion in Oakland, a large number of ships waiting to berth have been steaming in circles outside the port. The port rotations covering Long Beach and Oakland with a usual travelling distance of around 385 nautical miles (NM) between the two ports peaked at an average voyage distance for the larger container vessels of more than 1600 NM (see graph in figure 2).

Figure 2: Actual distance travelled between Long Beach and Oakland
(for 145 ships on 322 voyages from Long Beach to Oakland between 1st January 2020 and 13 June 2021)

Long Beach and Oakland do not stand alone. Figure 3 shows global figures for container ships waiting to enter ports.

Figure3: Number of container ships being stationary outside ports globally and outside China and U.S. West Coast ports between 1 October 2020 and 23 June 2021

Introducing slot management to ease port congestion

The maritime sector is putting increasing focus on seeking opportunities from digitalisation that can enhance coordination and synchronisation in the self-organised ecosystem of the maritime supply chain network. One promising initiative is the introduction of virtual vessel arrival and standardised data exchange for JIT arrival promoted by numerous stakeholders associated with the maritime industry.[1] However, JIT limits itself to a port to ship interface and could result in a one-sided port view which may cause concern for shipping lines particularly during times of port congestion.[2]

To overcome this and provide a more open management environment, we propose an expansion of the JIT arrival concept to incorporate a slot management concept that includes a dynamic view and management of JIT arrivals and departures. This would rely on shared data providing a common situational awareness for all involved actors of up-to-date progress and planning information on queues and waiting times associated with ports as maritime chokepoints. Such data sharing between all the actors involved in the port call process is already underway through the initiatives of Port Collaborative Decision Making (PortCDM) and Port Call Optimization.[3]

Slot management processes are widely used in many if not most other industries including aviation, land transport delivery, and even doctors’ appointments. However, unlike most other sectors, time slot management used for port calls must be particularly dynamic and capable of accommodating adjustment for the longer length of journeys involved and the likelihood of unpredictable changes such as weather, breakdown, delays in intermediate ports, and so on.

Figure 4 shows a number of typical time slot scenarios for the maritime supply chain. Scenario A is when the time of departure from the previous port enables just-in-time arrival at the subsequent port, possibly allowing for optimal steaming speed to destination.

When there are delays in departure time from the previous port (B in figure 4), also causing challenges for subsequent visits by other ships to that previous port, there are two options for a ship with respect to its destination port; either increase the speed of transit (option B1) to the next port or agree to a new slot time with the port of destination (option B2) and then travel at the speed originally planned or at an adjusted speed.

Figure 4: Typical scenarios for JIT shipping using time slots

When the infrastructure is constrained at the port of destination (C in figure 4), the following alternatives arise:

  • The ship stays alongside in the previous port as long as possible (option C1).
  • The ship anchors outside the port of destination (option C2).
  • The ship may anchor somewhere on the way towards the destination (option C3).

Concluding remarks

Introducing slot management underpinned by data sharing means that ships and ports can continuously share information on anticipated arrival and departure times. This is the basis for improving the management of delays and congestion along the maritime supply chain. It provides an open, data sharing environment where all parties can share a common situational awareness, make their plans accordingly and understand the impact on others. This is something that does not appear to occur regularly at present.

The maritime industry will benefit from managing uncertainties as they come with high costs for the entire supply chain network as the current surge in ocean container freight rates demonstrates. Acknowledging both the predictability of arrival and departure times will help the industry to move from the sequencing based on physical presence to virtual coordination to make an important step into an increasingly managed future.

[1] IMO (2020) Just In Time Arrival Guide – Barriers and Potential Solutions, BIMCO (2020). Optimisation and GHG reduction are key in new BIMCO just in time arrival clause, BIMCO (2013) Virtual arrival clause for voyage charter parties 2013

[2] Lind M., Becha H., Simha A., Larsen S. E., Ben-Amram E., Gnass M. (2021) Port call optimisation: Two sides of the same coin, Smart Maritime Network, 25/2-2021

[3] Lind M., Ward R., Bergmann M., Haraldson S., Zerem A. (2019) Digitalizing the port call process, UNCTAD Transport and Trade Facilitation Series No. 13, UNCTAD

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