Airport Capacity Analysis: When Do You Need a New Runway?
“Do we need another runway?” is one of the most expensive questions an airport can ask, and it is almost never answered by looking at the busiest day. The FAA answers it with a ratio: how close annual demand is running to the airport’s Annual Service Volume (ASV). This article explains how capacity is measured, what the demand-to-capacity ratio means, the planning thresholds that signal it is time to act, and why a new runway is the last alternative on the list, not the first.
Two ways to measure capacity
Airfield capacity is measured at two timescales, and both matter:
- Hourly capacity — the maximum number of aircraft operations the runway system can handle in an hour under a given condition (good weather vs. instrument weather, the runway-use configuration, the fleet mix). It is what drives delay on a peak day.
- Annual Service Volume (ASV) — a reasonable estimate of the annual operations the airfield can handle, accounting for the year-round mix of weather, configurations, and demand patterns. ASV is the yardstick for long-range planning.
The two are linked: ASV is derived from the weighted hourly capacities across the conditions the airport actually experiences over a year. A high peak-hour capacity does not guarantee a high ASV if the airport spends a lot of the year in a low-capacity configuration.
The demand-to-capacity ratio
The decision metric is the ratio of annual demand to ASV. As that ratio climbs, average delay per operation does not rise linearly — it rises gently at first and then sharply as the airport approaches its service volume. That non-linear curve is the whole reason capacity planning starts early: by the time delay is obviously bad, the airport is already deep into the steep part of the curve, and a major project takes years to deliver.
This is why the FAA frames capacity planning around two demand-to-ASV thresholds rather than a single “full” point:
| Demand vs. ASV | What it signals |
|---|---|
| ~60% of ASV | Begin planning capacity-enhancement studies — identify alternatives, start the analysis |
| ~80% of ASV | Improvements should be moving toward implementation, so capacity is in place before demand arrives |
| At / above ASV | Delay is significant and growing; the window to act ahead of demand has closed |
These are planning triggers, not pass/fail lines. Reaching 60% of ASV does not mean a runway is needed — it means it is time to study the question seriously, because the lead time on any meaningful fix is long.
Demand is a forecast, not a count
The “demand” side of the ratio is not last year’s operations — it is the forecast. A capacity analysis lives or dies on the activity forecast behind it: total annual operations, the peak-period demand, and the fleet mix all feed the capacity and delay calculation. A forecast that is FAA-consistent (compared against the Terminal Area Forecast) and properly built is the foundation; everything downstream inherits its assumptions.
A runway is the last alternative, not the first
A capacity shortfall does not equal “build a runway.” The FAA expects an airport to work through less costly, lower-impact alternatives first, in roughly this order:
- Operational and procedural changes — new approach procedures, revised runway-use configurations, air-traffic procedures, or technology that raises effective capacity without new pavement.
- Geometric improvements to the existing airfield — high-speed exit taxiways to clear runways faster, parallel or bypass taxiways, or holding-bay reconfiguration. Faster runway occupancy directly raises hourly capacity.
- Demand management — scheduling, pricing, or peak-spreading measures where applicable.
- New runway capacity — a parallel runway, a reconfigured crosswind runway, or a new runway, considered only when the lower tiers cannot close the gap.
A new runway is the most expensive, most land-intensive, and most environmentally consequential option — it triggers a full NEPA review, an ALP amendment, and a long capital program. The analysis has to show that the cheaper tiers genuinely cannot meet the forecast demand before the runway is justified.
Putting it together
- Build the forecast — annual operations, peak periods, and fleet mix, checked for TAF consistency.
- Establish ASV and hourly capacity — for the existing airfield, by configuration and weather condition.
- Compute the demand-to-ASV ratio across the forecast years and find when it crosses ~60% and ~80%.
- Test alternatives in order — procedural, then geometric, then demand management, then new pavement — each re-scored against delay.
- Document the justification — the chosen alternative, the delay it relieves, and the year it must be operational.
Answered this way, “do we need a new runway?” becomes a defensible chain: forecast demand, measured capacity, the ratio between them, the alternatives tested, and the one that closes the gap at the lowest cost and impact.
This article is a reference summary for planning use, not a substitute for the governing FAA text. Citations refer to AC 150/5060-5 (Airport Capacity and Delay) and AC 150/5070-6B (Airport Master Plans). The demand-to-ASV planning thresholds are general planning conventions — always verify current capacity methods and thresholds against the governing guidance and coordinate with your FAA Airports District Office before relying on a capacity finding. See the full airport planning glossary or the AvPlot toolkit.