There’s a lot we may not know about air travel—from the air in oxygen masks and cold cabin temperatures, to secret flight attendant codes and hidden airline cabins.

But have you ever thought about those boring airport runways that airplanes land and launch off of? Probably not. But without them, aircraft wouldn’t be able to lift off and fly you away or land at your next destination. Although these large areas of tarmac are distant thoughts in our heads, they still possess a few interesting facts that may surprise you.

Not All Runways Are the Same

That’s right, every runway is different. The legal definition of a runway is “a defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft”. Apart from that, runways can vary drastically from one another. For instance, the runway on Hebridean island of Barra is sand, Nevada’s Groom Lake Airport runway is salt, and McMurdo Sound Airport runway in Antarctica is ice. Moreover, differences also lie in the layout, size, and design of the runway.

Runways Vary In Size

There is no standard runway length, but the requirement is they have to be “adequate to meet the operational requirements of the airplanes for which the runway is intended”. However, the longer the tarmac, the more planes can land both in quantity and in size.

The largest airplanes in the world, such as the A380, need at least 1.86 miles of runway space to take off and land, whereas smaller planes need less space. Some of the biggest runways can be seen all over the world—from China’s Qamdo Bamda Airport tarmac, which stretches 3.42 miles, and Russia’s Ramenskoye Airport tarmac that’s 3.36 miles, to some of the world’s smallest like Juancho E. Yrausquin Airport tarmac in Saba, which is a mere 0.25 miles.

Runways Are Made Up of Various Materials

As you’ve just learned, runways are not all the same, as such, there are no specifics of what they have to be made of. However, runways are required to “be capable of withstanding the traffic of airplanes the runway is intended to serve.”

Usually, they are made from concrete or asphalt with ridges for gripping airplane tires. These ridges also play an important role when it rains by directing water away from the tarmac for planes to safely land and take off.

Runways Are Constantly Cleaned and Maintained

Just like any construction, maintenance is key in order to prevent damage and ensure the safety of aircraft takeoff and landing. This could be anything from cleaning and re-sealing, to removing rubber streaks remains from a skidding airplane, and renewing the entire surface with a new coat of concrete or asphalt.

But when does an airport know when it’s time to replace or renew? There are teams that scout the entire area on a regular basis to make sure it’s free from cracks and any strange objects (i.e. bolts or other metal articles) that could fly up into an airplane’s engine. If the runway requires major cleaning, it’s usually done overnight.