With the development of machines and automation to manage nearly everything in our lives, reliance on human initiative and decision is quickly becoming a thing of the past. However, as a result of this change, there is an ever-growing need for humans to effectively interface with machines. This month's mishap addresses the importance of prudent consideration in the design of the human-machine interface. During morning rush hour in London on Oct. 5, 1999, a commuter train passed a red signal into the path of an oncoming high speed train at Ladbroke Grove Junction, killing 31 people and injuring many others. The mishap investigation pointed to several problems related to how the driver and signalers interfaced with the equipment and displays around them. At NASA, when we rely on human action, we must be careful to design for human capability and limitations. We must design systems that consider human expectations and logic. To ensure success, we must supplement these designs with effective training and sufficient experience to enhance the likelihood that the proper actions are taken.