While taxiing toward the runway for takeoff a passenger on a flight at JFK International might observe a marker indicating "Runway 4-22." In fact, on that passenger's next departure from LaGuardia Airport he or she might see the identical designation for a runway at that airport. What's going on? What's the meaning of "4-22" that you see it at both airports?
The first thing you have to know is that the representation "4-22" refers to two runways, runway 4 and runway 22. Yes, it is a single strip of pavement, but depending upon which direction the aircraft is traveling, it is either runway 04 or runway 22. The number used is the one closest to where the plane makes initial contact with the runway, either in takeoff or landing.
Incidentally, the other runway at LaGuardia is 13-31. Those mathematically inclined might have noticed that 4-22 and 13-31 both represent gaps of 18. That's a clue to the numbering of runways. Every runway has a gap of 18 between the numbers at either end; know the number at one end and you know the number at the other end of the same runway.
The reason for this standard gap of "18" is that all runway numbers are determined from the compass direction to which they point, and all runways are a straight line. Consider that a circle is 360 degrees. North is 360; east 90, south 180, west 270. For convenience, and maybe to save some paint, we drop the zero at the end. Thus, a runway "pointing" west will have the number "27" painted on the ground (in a size visible from some altitude) at its starting point, perhaps two miles east of the runway's western end. Conversely, the other end of the same runway will have painted the number that is 180-degrees from 270 degrees -- that is it will be facing due east, or 90 degrees, and be designated runway "09."
So, let's get back to the actual numbers at LaGuardia, 4-22 and 13-31. If you are departing for Boston, you'd rather see the pilot begin the takeoff roll on runway 04 than 22. All things being equal in terms of wind direction at takeoff and air traffic control routing once airborne, you've got the best shot with Runway 04 because it is pointing toward the north-northeast. Returning from Washington, D.C.? Runway 36, heading due north, would be your choice.
I relate this information about runway numbering with one particular experience in mind. When I was the spokesman for the National Transportation Safety Board (NTSB) I was briefing reporters in the aftermath of an airplane crash. I said that the plane had departed from the airport on "Runway Nine." One reporter, clearly unfamiliar with the basis for runway numbering, challenged me instantly. He was very agitated: "Runway 9? What are you talking about? Everyone knows there are only two runways at this airport."
Can you imagine if I had said "Runway 27"?