Positive guidance in traffic control

A high payoff, short-range way to enhance the safety and opera- tional efficiency of substandard facilities is through positive guid- ance. This approach joins the highway engineering and the human factors technologies to produce an information system matched to the facility characteristics and driver attributes. It is based on the premise that a driver can be given sufficient information where he needs it and in the form that he can best use to avoid hazards. The application of positive guidance requires an understanding of the driver's task and his use of information. Decision-making failures attributable to information system deficiencies are identified as factors leading to accidents and inefficient traffic operations. A driver gathers information from many sources. He handles it in a decision-making process, and then translates these decisions into control actions. This task is composed of many discrete activities which may be grouped in three levels. The control level relates to the physical operation of the vehicle. The guidance level relates to selecting and maintaining a safe speed and path. Here the driver gathers information from many sources and relies on experience, judgment, estimation, and prediction. The navigation level relates to trip planning, route following, and direction finding. Information at this level is usually intermittent and highly verbal. Control and guidance level failures increase the probability of accidents (catastrophic system failures). Navigation level failures lead to delay, confusion, and other inefficiencies (noncatastrophic system failures). Positive guidance is of greatest benefit to the driver when he must recognize and respond to situations and events which are often hazardous. The basic guidance task is lane placement and road following. Obstacle avoidance is part of and integrated into this task. Superimposed on the basic task are more complex guidance tasks that include car following, overtaking and passing, avoiding pedestrians, etc. These tasks are time shared with each other, and with control and navigation activities. When events occur near each other, the amount of time available to receive and process information is limited, and the margin for error is reduced.