Airport Capacity and the Case for Congestion Pricing

The global aviation system is approaching a capacity crisis. The world's busiest airports are operating at or near their physical limits, with runways, terminals, and airspace stretched thin by demand that has recovered from the pandemic and continues to grow. Building new runways or airports takes decades and costs billions. Meanwhile, the economic value of access to congested airports — measured in the prices airlines will pay for landing rights — has soared into territory that raises fundamental questions about how a scarce public resource should be allocated. Airport capacity and its management sit at the intersection of economics, politics, engineering, and environmental policy, and the tensions are intensifying.

What Constrains Airport Capacity?

Airport capacity is determined by whichever element — runway, terminal, airspace, or ground infrastructure — imposes the tightest bottleneck. For most constrained airports, the binding constraint is the runway system.

A single runway can handle approximately 30 to 40 movements (arrivals plus departures) per hour under instrument flight rules, depending on the mix of aircraft types, weather conditions, and the separation standards applied by air traffic control. Parallel runways, if spaced far enough apart for independent operations (at least 1,035 meters under ICAO standards), roughly double this capacity. But even four-runway airports like London Heathrow (LHR) — which operates two closely spaced parallel runways in alternating mode, effectively functioning as a single-runway airport for capacity purposes — can hit a ceiling of roughly 480,000 annual movements, a figure Heathrow has operated near for more than a decade.

Terminal capacity is the second common constraint. A terminal can only process a certain number of passengers per hour through check-in, security screening, and immigration. Expanding terminal capacity often requires demolishing and rebuilding, which must be done while the airport continues to operate — the equivalent of renovating a house while living in it. New York LaGuardia (LGA) has been undergoing a complete terminal replacement since 2016, a process that has taken nearly a decade and cost over $8 billion, all while handling tens of millions of passengers annually.

Airspace capacity, controlled by national air navigation service providers, is an often-overlooked constraint. The approach and departure routes to a major airport must be carefully designed to separate arriving and departing traffic streams, manage noise exposure, and avoid conflict with nearby airports. In the New York metropolitan area, where JFK, LGA, and Newark (EWR) share overlapping airspace, the interdependence of three major airports creates capacity limitations that no amount of runway construction at any single airport can solve.

The Slot System: Rationing by Committee

At the world's most congested airports, access is rationed through a system of landing and takeoff slots, coordinated under the Worldwide Airport Slot Guidelines (WASG) maintained by IATA. A slot is permission to use an airport's runway at a specific date and time. Airlines that held slots in the previous equivalent season have "grandfather rights" — the right to retain the slot in the next season, provided they used it at least 80% of the time (the "use it or lose it" rule, briefly suspended during the pandemic).

New entrants seeking slots at congested airports must petition the airport's slot coordinator, typically an independent body, for any capacity that becomes available — slots surrendered by airlines, slots recovered through the use-it-or-lose-it rule, or additional capacity created by infrastructure improvements. The process is theoretically non-discriminatory, but in practice, incumbent airlines at slot-controlled airports hold the vast majority of slots and have little incentive to surrender them.

Heathrow is the most extreme example. Virtually all slots are held by incumbent carriers, primarily British Airways (which holds approximately 55% of Heathrow slots) and its oneworld alliance partners. New entrants face a near-impossibility of obtaining commercially viable slot pairs (a departure slot matched to a return arrival slot at a useful time of day). The secondary market for Heathrow slots, though not formally recognized by IATA, is robust: Oman Air reportedly paid $75 million for a single pair of daily Heathrow slots in 2016. American Airlines acquired a slot pair for $31 million.

The Economics of Scarcity

From an economist's perspective, the slot allocation system at congested airports is deeply inefficient. Slots are distributed based on historical precedent rather than economic value. An airline using a peak-hour Heathrow slot for a short-haul flight to a destination with modest demand generates less economic value — measured by passenger willingness to pay, connectivity created, or GDP contribution — than an airline that would use the same slot for a high-demand long-haul route. But the historical allocation system gives the incumbent the right to retain the slot regardless of how it is used.

The absence of market-based pricing for airport access means that the price airlines pay for using a congested runway bears no relationship to the scarcity value of that access. Landing fees at Heathrow, while among the highest in the world, are set by the airport regulator based on the airport's cost base — they reflect the cost of providing the infrastructure, not the economic value of accessing it. The result is a system where landing fees are the same whether you use the runway at 7 AM on Monday (peak demand, every slot taken) or 3 AM on Tuesday (minimal demand, plenty of capacity available).

This is the classic economic case for congestion pricing: if the price of access reflected demand, airlines would face incentives to shift operations to less congested periods, use larger aircraft to carry more passengers per movement, or consolidate frequencies. The runway capacity that currently supports three half-empty flights to the same destination might be freed up for other routes if the price of each slot reflected its scarcity value.

Congestion Pricing Models

Several congestion pricing models have been proposed for airports, though none has been implemented at a major hub in its pure form:

Peak/off-peak pricing is the simplest approach. Airports would charge higher landing fees during peak hours and lower fees during off-peak periods, creating financial incentives for airlines to shift operations toward less congested times. This model is used in a rudimentary form at some airports — Sydney (SYD), for instance, charges a premium for peak-period movements — but the differentials are rarely large enough to change airline behavior meaningfully.

Auctioning slots is the most market-oriented approach. Instead of allocating slots through the grandfather system, slots would be auctioned to the highest bidder, with revenue flowing to the airport or government. Proponents argue that auctioning would ensure slots are used by airlines that value them most — a proxy for routes that serve the most passengers or generate the most economic activity. Opponents, particularly incumbent airlines, argue that auctioning would transfer billions of dollars in value from airlines to airports, increase costs for passengers, and destabilize hub operations that depend on coordinated waves of arrivals and departures.

Slot trading is a compromise that preserves grandfather rights but allows market forces to reallocate slots over time. The UK formally recognized secondary slot trading in 2024, making explicit a practice that had occurred informally for years. Under a trading system, airlines can buy and sell slots at market prices, allowing new entrants to acquire access by purchasing slots from incumbents willing to sell. The US permits slot trading at certain airports under different rules. The European Commission has debated mandatory trading systems but has not imposed them.

Political Barriers

The intellectual case for congestion pricing is strong. The political barriers are enormous. Airlines, particularly flag carriers with large slot portfolios at their home hubs, view slots as assets — some airlines list slot values on their balance sheets — and fiercely resist any reform that would diminish their holdings. Hub carriers argue, with some justification, that their operations create network connectivity that benefits the broader economy and that would be disrupted if slots were reallocated by price alone.

Governments face conflicting pressures. They want airports to operate efficiently (favoring market-based allocation) but also want to maintain service to politically important destinations (which might lose service if price alone determined slot use), protect national carriers (which might be outbid by wealthier foreign airlines), and avoid the public backlash of higher ticket prices (which airlines would pass through to passengers if landing fees increased).

Environmental groups add another dimension. Congestion pricing could reduce total aircraft movements by encouraging larger aircraft and fewer flights — a desirable outcome for noise and emissions. But it could also increase total passenger throughput by making each movement more productive, potentially increasing the airport's overall environmental footprint even as per-movement impacts decline. The interaction between capacity management and environmental policy is complex and context-dependent.

The Expansion Alternative

The alternative to better managing existing capacity is building more of it. But airport expansion has become one of the most contentious infrastructure debates in the developed world. The campaign for a third runway at Heathrow has lasted over 20 years and survived multiple government reviews, public inquiries, court challenges, and political reversals. As of 2025, construction has not begun, and the project's future remains uncertain despite being formally approved by Parliament in 2018.

In Germany, the expansion of Frankfurt (FRA) with a fourth runway in 2011 was achieved only after decades of litigation and the largest environmental impact assessment in German history. Munich (MUC) has sought a third runway for over a decade but was blocked by a 2012 public referendum in which Munich residents voted against the project. In the United States, no major new commercial airport has been built since Denver International (DEN) opened in 1995.

In contrast, the Middle East and Asia have built aggressively. Istanbul (IST) in Turkey opened in 2018 with an ultimate planned capacity of 200 million passengers. Beijing Daxing (PKX) opened in 2019 with capacity for 72 million passengers in its first phase. Dubai is planning Al Maktoum International Airport (DWC) as a replacement for DXB, with a planned capacity exceeding 260 million passengers annually. These projects reflect a different political economy: centralized decision-making, state ownership of airports, and a strategic view of aviation as an engine of national development rather than a source of local nuisance.

Demand Management: Beyond Pricing

Some capacity constraints can be addressed through demand management techniques that do not require construction or pricing reform. Next-generation air traffic management systems, such as the Single European Sky ATM Research (SESAR) program and the US Next Generation Air Transportation System (NextGen), promise to increase airspace capacity through more precise navigation, tighter aircraft separation, and dynamic routing. Performance-based navigation (PBN) procedures, which use GPS-guided curved approaches instead of straight-in ILS paths, can increase the number of usable approach routes and reduce airspace conflicts.

Airport Collaborative Decision Making (A-CDM), a framework promoted by Eurocontrol, improves the efficiency of existing capacity by sharing real-time data between airports, airlines, ground handlers, and air traffic control. When all parties know the actual status of every turnaround — whether fueling is complete, whether passengers have boarded, whether the pushback tug is in position — the airport can sequence departures more precisely, reducing runway idle time and taxi delays. A-CDM has been credited with recovering several movements per hour at airports where it has been implemented, equivalent to adding capacity without building anything.

Looking Forward

The capacity challenge is not going away. Global air passenger numbers are projected to double by 2040, with the strongest growth in Asia and the Middle East. The airports that will cope best are those that combine infrastructure investment with intelligent demand management, fair and transparent access allocation, and the political courage to implement pricing mechanisms that reflect the true scarcity value of their resources.

Congestion pricing is not a panacea. It will not build runways, will not silence community opposition to expansion, and will not resolve the tension between environmental protection and economic growth. But it addresses a fundamental inefficiency in how one of the world's most valuable public resources — access to a slot at a congested airport — is currently allocated. The question is not whether the economics make sense. They do. The question is whether the politics will ever allow the economics to prevail.