Airport Madness 3 will offer the users a limited ability to assign different runways. As in the real world, there is always some flexibility but there are very few airports that operate in free-for-all fashion.
At any airport there are never enough taxiways. Whenever two aircraft stare each other face-to-face on the same taxiway, there is rarely enough room for them to pass, and turnarounds are difficult. It's not a dangerous situation due to the low speeds involved, but the pilots do have to stomp on their brakes, shut down and call for a tug. Many a real-world controller has inadvertently created this very scenario! And when they do, they are said to earn the "Golden Tow Bar Award".
As much as I would love to give users absolute taxiing freedom, I'm going to keep it realistic. When a 737 calls ready for taxi clearance, you will have the option of assigning a couple of different runways, but there will be a structured flow. For example, by default arrivals will come to you established on final approach for runway 06 or runway 12. You can cross them back and forth between the two runways if you like. Similarly, when a departing aircraft calls for taxi clearance you can taxi them for either runway 06 or runway 12. This maintains a natural flow of traffic.
If you get bored of the 06/12 operation, you can choose to operate the airport using runways 24 and 30 in the reverse fashion, still maintaining a natural flow. You will not be permitted to get any more creative than this, however. In real life, if you were to taxi an aircraft for runway 24 with arrivals using 06 your coworkers would hate you :)
