THE MODEL THAT DIDN'T WORK.

The article presents information on a model implemented to determine traffic signal timing in a province known as Tuah. The model was duly validated for Tuah. The supervising traffic engineers were, however, not impressed and loudly proclaimed their reluctance to engage in further funding until a practical problem could be solved, said practical problem being the congestion at the most heavily congested intersection in Tuah. The problem was that rush-hour traffic could not get off the freeway and through the interchange fast enough to avoid queuing back onto the freeway. Realizing that the two problems were interconnected, the traffic engineers took much data, created the proper input to the computer, and adjusted the signal timing on the simulation model until the traffic showed a near-optimal improvement. One year later, two traffic engineers from the country of Falicornia discovered that the interchange had been modeled incorrectly-that a Markovian assumption in the model of the interchange simply did not hold.