Originally Posted by
Dave Gittins
In the USA some airports have more than two. Denver is fun they have 4 parallel 34 and 35 left and right of each and 25 and 26 going the other way. I've been on finals on one runway (35R) at KDEN in a 74 with a united 777 landing parallel (34L) a mile to the side.
ATL is great for this too.
Five parallel runways, and it's very common to have paired landings where two aircraft are parallel on approach. They use the outer runways for arrivals and the inner (closer to the terminal) for departures.
Back to OP's original question, I've observed very tight single-runway separations at DCA... departing aircraft might clear the runway ~10-15 seconds before arriving aircraft touches down at the approach end. I'm sure the correct minimums are maintained but it's amazing to watch.