Steffen considered various methods, such as boarding people in blocks, at random, and in window seats first.

FORBES: Sometimes Science is Behind the Curve

He also found that boarding at random is faster that boarding by blocks.

FORBES: Sometimes Science is Behind the Curve

Its officers began to search people, pretty much at random and often with little cause, on the streets, in housing estates and in apartment blocks.

ECONOMIST: The dark side of zero tolerance