From simple single runway regional airfields, to the massive sprawl of international airports, I never get tired of looking at airports. But I’ve always wondered what the logic behind the runway layouts was.
Some have intersecting runways at seemingly random angles, while others are oriented in strict north/south and east/west directions. They’re often massive projects of pride for cities and countries, showcasing interesting architecture, and in some cases, entirely new landforms built out into the ocean.1
It’s no surprise there is plenty of logic behind the layouts. As with most infrastructure, it all depends on the era they were built. Back when planes were smaller and less sturdy, they needed to take off and land heading into the wind. Building runways in various directions gave pilots several options depending on which way the wind was blowing. Even to this day, all planes have a cross wind limit, meaning they can’t take off or land if the crosswind exceeds the plane’s given limit.
Modern, larger planes are able to handle stronger crosswinds, so orienting runways in parallel with no intersections has become more common. Many airport have been or are being reconfigured to accommodate for this. These layouts also allow for more efficient use of land, and aid in managing traffic.
Of course, local geography plays a role as well. Taking off or landing over water reduces noise disturbance. Local wind patterns play a large role, as well as available space. Parallel runway orientation saves on land use, while perpendicular orientation can allow for more efficient airline traffic.
The FAA has a nice tool for finding airport diagrams here.
Airports like London-Heathrow and O’Hare have been rearranged to take advantage of current land allotments, opting for more parallel runways.
Denver International Airport airport is a great example of a large, modern airport using strictly parallel and perpendicular runways.
Liberal Mid-America Regional Airport showcases an older design with runways at many angles, almost intersecting. Several of the runways are no longer in use to accommodate modern aircraft and flight patterns.
- Of course, these aren’t without controversy. Why wants to deal with the noise? Who wants to give up their homes for new runways or expansions. And who wants to fund these projects? If there ever was a NIMBY project, airports certainly qualify. ↩︎