Sit down for this.
It sounds ridiculous. Like saying pie is the best sort of breakfast. But of course, pie is the best sort of breakfast, depending on how you want to optimize your breakfasts. (Your correspondent's primary criterion is sugary deliciousness.)
Here's how it breaks down for Dutch engineer Henk Hesselink:
Pilots like to land into a headwind. Crosswinds, they're not so excited about. Now imagine a traditional, straight runway: there's probably wind. It's probably blowing from a particular direction — but the runway's not moving. Which means that whether the wind is a headwind or a crosswind or a whatever-wind can only be finessed so much.
Now imagine a circular runway: the pilot can choose from a range of approaches — and thus, he's allowed some degree of flexibility in positioning his plane relative to those winds. Perhaps a crosswind becomes a headwind.
Also, Hesselink notes, no more worrying about overshooting the runway ... since you'll be going in a circle. Also, he thinks, multiple aircraft could land on a single runway more or less simultaneously — meaning a single circular runway could have the same landing capacity as four traditional runways.
Sounds weird. But: What out-of-the-box idea have you had today?