Human factors recommendations for TMC design - traffic management center

Public Roads, May-June, 1999 by Nazemeh Sobhi, Michael Kelly

Traffic incidents may have a detrimental effect on traffic congestion from the time they occur until long after the actual incident is cleared. Prompt identification and clearance of incidents can minimize this damage.

Traditional incident detection methods, typically relying on phone notification by citizens or a fortuitous discovery by a law enforcement officer, may require relatively long periods of time to detect and begin clearing accidents. Intelligent transportation systems (ITS) technology, including closed-circuit television, traffic-flow sensors, and computer-based incident detection systems, can identify roadway incidents much more quickly. In addition, traveler information systems can alert drivers approaching an incident to the need to drive cautiously to avoid a secondary accident.

An ITS-class traffic management center (TMC) incorporates a large number of sensors to collect and communicate traffic-flow data. They may employ data fusion and automated information processing to combine and translate the information into a form that can enhance operators' knowledge of the status of the roadway environment. A TMC can automate some routine decisions and actions to help manage the operators' workload. Finally, a TMC prorides new channels to communicate information to drivers and vehicles, including presentation of brief messages on variable message signs (VMS) and presentation of more complex information on short-range highway advisory radio (HAR) transmitters.

The success of advanced traffic management systems (ATMS) operations ultimately depends on how the human operator interacts with the systems' computers and devices. The human operator is a critical component whose capabilities and limitations must be integrated into the design and operation of a TMC. The need to integrate human operators into the traffic management system dictates that the principles of usercentered design and human factors engineering must be incorporated into the overall system design and system engineering process.

A series of experiments were conducted in a high-fidelity TMC human factors research simulator to address some of the important questions that were being asked about how best to integrate the human operator into the high-technology TMC. Some of the questions concerning systems for data collection and information promulgation are discussed in this article.

Methods of Controlling Remote CCTV Cameras

TMCs in many urban areas rely heavily on remote, closed-circuit television (CCTV) cameras for maintaining surveillance of the roadway system. A TMC operator in such a system may have access to dozens, or even hundreds, of remote cameras. These cameras are used to detect incidents, such as traffic accidents or debris on the roadway; to verify incident reports received by other means; to monitor incident clearance; and to maintain surveillance of the general traffic flow.

With such a large number of remote cameras in use, a TMC operator may spend considerable time selecting remote cameras for viewing on available monitors and manipulating (panning, tilting, and zooming) the camera view. If the design of the cameras affects the cameras' effectiveness and ease of use, the design will consequently affect the effectiveness of the entire traffic management system.

The human factors design issues associated with these cameras include:

* What type of interface is best for selecting a remote camera for viewing? Some implementations require the operator to type in an identifier string on a keyboard or keypad while others allow selection of a camera icon off a map using a finger touch, mouse, or other pointing device.

* What type of operator interface is best for manipulating the camera? Many implementations use a dedicated joystick or button-box. Although these devices are used only for camera controls, designers wonder whether keyboard or mouse controls (devices that are present anyway) could be used effectively to control the remote cameras without adding further clutter to the console.

* Are camera presets (i.e., predefined pan, tilt, and zoom coordinates arranged in a set sequence) preferable to unrestricted manual control of cameras? These presets, usually mediated by an add-on system that increases cost, allow the user to specify the views that are of interest and preclude views of off-the-road scenery. Presets are arranged in a sequence and the operator's control actions cause the camera to progress through the sequence of preset views.

Four different manual interfaces were tested for selecting and controlling remote cameras: the joystick interface, the keyboard interface, the touch-screen interface and the mouse interface.

In the joystick interface, left and right movements of the joystick result in left or right pans of the camera view. Backward and forward movements of the joystick result in downward and upward tilts of the camera. Zooming is accomplished by simultaneously pressing a button on top of the joystick and moving the stick forward or backward. Cameras are selected for viewing by typing an identifier string using the numerical keypad of the computer keyboard. This configuration matches a common arrangement, currently in use in TMCs, that features a joystick and associated keypad to select and control cameras.