Everytime I happen to drive (rarely these days since I use ZipCar), I inevitably have to park in a garage somewhere. And each time I wonder why no one has implemented what to me is a trivially simple solution to finding a parking spot in parking garages, especially those at airports. Here's my idea. If you decide to implement it, send me a million dollars. If you have already implemented it, then

Each parking spot in a garage has an RFID transmitter and receiver oriented in such a way that when a vehicle is parked in the spot, the receiver cannot get the signal. (I guess it doesn't have to be RFID...even a line-of-sight laser would work.) A receiver that is getting a signal is considered ON...all others are OFF.

Each receiver is networked to the parking garage's computer. The computer runs a program that sorts parking spots by proximity to elevators/exits. Only receivers that are ON are included by the program.

When a car pulls into the parking lot, the program prints out a ticket containing the location number (eg. B-4) of the first spot in the list (i.e. the first available spot that is nearest to the elevator/exit). The driver places the ticket on the dashboard so it is visible from the outside, drives to the spot and parks (the spot will be vacant). If he/she parks in a spot that's different from what's on the ticket, a hefty fine is levied (easy to track because the location of the ticket can be used to make this determination).

This is a simple solution, requires no driving around endlessly looking for a spot and optimizes traffic patterns in the garage i.e. fewer fender benders.