Why New Runways Do Not Always Increase An Airport's Flight Capacity

Published Nov 6, 2026, 3:01 PM EST Based in the UK, Josh is a keen writer with a degree in Military History. Having worked previously as a financial journalist, he has covered the aviation industry extensively, reporting on airlines' results and monthly passenger statistics in the aftermath of the pandemic, alongside the likes of regulation around sustainable fuels, and the prospects for hydrogen-powered commercial flight. He joins Simple Flying with a lifelong love of all things aviation. Airport infrastructure projects have been a hot topic this year. From Australia to Asia to the Middle East to the United States, new airport openings and expansions are in progress across the world. In any case, building or even adding to each airport will have been a far more complicated process than it may have appeared on the surface. In particular, planners have to carefully consider an eye-watering number of factors when building a runway alone. Where there is another runway in operation close by, the task becomes even more difficult. Simply put, it is by no means a matter of laying the groundwork and letting the aircraft move in. Airports Do Not Have Full Say Over Capacity The harsh truth for airport operators has previously been summed up by global trade association Airports Council International (ACI). “The capacity provided by the airport system is determined by multiple factors, many of which are not directly within an airport operator’s control,” it wrote in a 2019 research paper relating to air operations in Europe. These factors primarily include an airport’s runway or runways, its apron, terminal infrastructure, and the surrounding airspace. While planners may have full autonomy over where runways are positioned and how many there are, a lack of apron space for aircraft to move about or park on the ground could prevent the landing strips from operating at full capacity, for instance. Similarly, terminal space may be plentiful, but busy local airspace may mean air movements are capped, so the number of passengers that could in theory be processed by an airport will never be met. All of that goes to say that each factor matters for lifting capacity, but it can only do so in practice if the other considerations are addressed. Local airspace restrictions are arguably the trickiest for airports to navigate. Authorities can plan and lay out infrastructure on the ground as well as possible, but the traffic that can actually use it will be dependent on what is nearby. Its own designated controlled airspace — or Terminal Maneuvering Area — might overlap another airport’s, say, or something as simple as noise restrictions could be in place and so limit operations at certain times. When adding runways, planners must consider these factors before breaking ground. Existing Airport Facilities Have To Keep Up Among the most obvious constraints to growing capacity by opening a new runway is the airport itself. That stretches beyond just aprons and terminals. Whether it be public transport, roads, or car parking spaces, getting passengers on and off site is one issue. Add in the need for additional check-in counters, security checkpoints, passenger waiting areas, and aircraft docking gates, and more flights will mean more stress on every part of an airport. There is no solid guarantee that building all of that will drastically improve capacity, too. According to a 1982 Congressional study, efforts undertaken in response to growing demand for flights tended to have the largest impact on reducing delays. Of course, where new long runways are built and properly equipped for independent flight rules (IFR) operations, capacity could increase. That said, factors such as the original runway configuration meant that the jump could be anywhere in the region of 20% to 50%. While potentially significant, the cost and effort behind building an extra runway could deem the entire project unviable. An 11,000-foot (3,353-meter) runway with its basic safety area covered 130 acres (52.6 hectares), the study noted. Combined with other necessary clear zones, the area directly affected stretched to three or four times that. To put that space to work, the airport had to bring the rest of its infrastructure up to scratch. All of that effort risked going to waste when the other existing landing strip or strips were taken into consideration as well. Vicinity Of New Runway To Another Outside upgrading airport infrastructure and building a new runway, its location relative to existing operational strips is key. Where two or more runways run parallel, spacing between aircraft making approaches in the same direction at the same time must be ensured. Such simultaneous same-direction operations, as the United States’ Federal Aviation Administration (FAA) dubs them, require visual flight rules (VFR) conditions, maintained two‐way radio communication with each aircraft involved, and a minimum distance between the centerlines of each runway. Where heavy aircraft — so widebodies like the Boeing 787 and Airbus A350 — were involved, that minimum distance was historically 700 feet (213 meters). Changes brought in earlier this year have since required such close approaches to be staggered. Either way, using runways in close proximity simultaneously relies on good weather. Poor conditions can require much greater distances between adjacent aircraft. At airports with precision runway monitor (PRM) systems that allow simultaneous instrument approaches, a distance of 2,500 feet (762 meters) is needed between landing strips. If not available, that figure can stretch to 4,300 feet (1,311 meters). Naturally, these rules reduce the risk of aircraft straying into each other’s paths, including in instances of go-arounds. They also ensure air disturbed by one, known as wake turbulence, does not destabilize another. Wake turbulence can be powerful enough to flip a pursuing or nearby aircraft in extreme cases. Sometimes, however, the vicinity of one runway to another is just too close, and extra runways do not always equate to additional capacity. San Francisco International Airport: A Prime Example According to the FAA, just four airports globally conduct PRM approaches as it stands: Hartsfield-Jackson Atlanta International Airport (ATL), Chicago O'Hare International Airport (ORD), Detroit Metropolitan Wayne County Airport (DTW), and Sydney Kingsford Smith Airport (SYD). Elsewhere, when parallel runways are too close, air traffic controllers can be limited in how they handle arrivals and departures, especially in the event of bad weather. San Francisco International Airport (SFO) offers a prime example. Though it has two sets of parallel runways, they sit just 750 feet (229 meters) apart from each other in each direction. The airport had been allowed to use each adjacent set simultaneously until recently, before the FAA effectively banned the practice in response to a fatal crash in Washington, DC, last year. This allowed a maximum arrival rate of around 54 aircraft per hour. Now, though, all aircraft flying into the airport must follow a staggered, diagonal sequence along the final approach path. That, in turn, has reduced the arrival rate to about 45 per hour currently, even in fair conditions. During periods of poor visibility, that drops further to 36 landings an hour as arriving aircraft are placed in a single-file pattern. Needless to say, the vicinity of the two sets of parallel runways at SFO has done little to aid capacity of late. Even without bad weather, other issues can severely constrain operations around airports, regardless of the number of runways available. Air Traffic Control Staffing: Another Major Consideration Behind all the physical infrastructure needed for an airport to grow capacity are the humans to run it. Responsibility for how runway systems are managed ultimately falls to air traffic controllers. That is, selecting an appropriate configuration and sequencing flights to use falls to those in the control towers. When multiple landing strips are in play, that all becomes more complex and may even require additional monitoring positions. Any shortage of air traffic control personnel can limit the feasible set of configurations available at an airport as a result, as concluded in a 2026 review of runway systems published in MDPI. Unfortunately, such shortages are a global issue today. An aging workforce and high training requirements are said to have driven a trend of cross-border recruitment across the industry, per Reuters. Staff shortages have already contributed to flight disruptions in major markets like Australia, the US, and Canada; meanwhile, estimates call for 71,000 new air traffic controllers across the world by 2034 in order to meet demand. Without them, airports' efforts to increase capacity risk becoming obsolete. Busy Airports Need New Infrastructure Most, But It Is Most Difficult To Build So, simply building a new runway is by no means the only thing airport officials have to consider when looking to increase the number of flights they can process. London Heathrow Airport (LHR) is one site where the debate around adding a strip has been long-running. Considered to be among the most slot-constrained airports in the world, Heathrow is in the process of seeking planning permission for its expansion. In its case, the UK government has laid out key tests that any solid plan will be assessed against. That includes the expansion's economic impact, environmental cost, and compliance with air quality and noise regulations. Again, that means further considerations outside of actually building the runway, synchronizing operations, upgrading infrastructure at the site, and whether there will be enough air traffic controllers when the time comes — which really affects capacity.