Introduction

Each year billions of dollars are spent to develop, manufacture, operate, and maintain various types of engineering systems throughout the world. Their safety and failure due to human error have become a pressing issue because of a large number of accidental deaths and a high cost. For example, in the United States automobile accidents on highways alone cause around 42,000 deaths annually and, in 1994, the total cost of motor vehicle crashes was about $150 billion to the United States economy [1-4]. Furthermore, around 70-90% of transportation-related crashes are due to human error to a certain degree [1].