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Publication Number: FHWA-RD-95-197
Date: December 1996

Development of Human Factors Guidelines for Advanced Traveler Information Systems and Commercial Vehicle Operations: Comparable Systems Analysis

 

Auditory Information Display

 

A goal of the TravTek system was to use voice to present navigation and traffic information without creating a visual distraction (Means, Carpenter, Szczublewski, Fleischman, Dingus, and Krage, 1992). Synthesized voice is used extensively in the TravTek system, providing route guidance instructions, navigation assistance, and traffic information. Non-verbal auditory signals are also used as feedback for button presses, as well as prompting for screen glances when voice functions are deactivated. Voice functions are controlled by the driver through the use of four buttons located on the steering wheel. These buttons are labeled "WHERE AM I?," "REPEAT VOICE," "TRAFFIC REPORT," and "VOICE GUIDE." The voice function controls allow a driver to select the types of information heard through voice, allowing all voice messages to be disabled if desired.

 

Where Am I?

The WHERE AM I? function provides information on the name of the next cross street and the vehicle's current street location/heading. Each press of the WHERE AM I? button elicits a single message with location information. Special messages have been formulated to accommodate situations in which the vehicle is not situated on a known street, or there are no known cross streets ahead of the vehicle (Means et al., 1992).

 

Repeat Voice

The REPEAT VOICE function enables the driver to replay the most recently spoken voice message. The message, when repeated, is prefaced by "The last message was..." The replay is a literal repeat, as opposed to a functional one. Even if the information imparted by the message has changed since the message was originally spoken, the original text of the message is spoken in the replay. The repeatability of a message lapses after a short period to avoid repeating messages in which the information content is extremely outdated. After the specified period, a button press of REPEAT VOICE produces the message "No recent message to repeat."

 

Traffic Report

The TRAFFIC REPORT function provides a verbal traffic advisory that reports known traffic problems. Traffic data are broadcast once per minute to the vehicles from the TravTek Traffic Management Center (TMC). Traffic data contain information on congestion problems within the TravTek map area, as well as details on incidents and construction when this information is known.

Onboard the vehicle, the traffic data are displayed on the map using incident and congestion icons. Traffic problems are filtered for relevance to the vehicle's location and route. With each new broadcast, a voice traffic message is formulated to describe each geographically relevant traffic problem. Voice traffic messages contain information on the location, cause, and severity of traffic problems. The set of relevant traffic messages constitutes the voice traffic report. When the TRAFFIC REPORT function is activated by a button press, the voice begins to state the current traffic report, with messages ordered by urgency and proximity to the vehicle. A subsequent button press will terminate the report. While the TRAFFIC REPORT function remains activated, all new, relevant traffic problems are presented as subsequent TMC broadcasts are received (Means et al., 1992).

At the outset of a trip, the TRAFFIC REPORT function defaults to OFF. Voice traffic reports are only presented if requested by the driver. When the TRAFFIC REPORT function is switched off, then back on, the full relevant, ordered set of traffic messages is repeated, allowing the driver to hear all traffic problems.

 

Voice Guide

The VOICE GUIDE button enables and disables voice route guidance instructions. Voice guidance messages describe upcoming route maneuvers, as well as indicating an off–route condition. Up to three voice messages may accompany each upcoming maneuver. If the distance to the maneuver is so great that the driver need not attend to it yet, the voice guidance message specifies only the distance to the maneuver, corresponding to a straight–ahead arrow on the visual display (e.g., "Ahead, next turn in three and four–tenths miles."). At a shorter distance to the maneuver, when the driver must get into the appropriate lane in anticipation of a turn, a "near turn" message is stated. The near–turn message contains the distance to the maneuver, as well as the name of the turn street and the type of maneuver (e.g., "make a hard left" or "bear right"). A typical near–turn message is "In eight–tenths miles, turn right onto the ramp to I–4 East." This corresponds to a change in the guidance display, which now depicts the geometry of the maneuver intersection and displays the name of the turn street. Just before the maneuver intersection, at a point where the driver can be expected to visually identify the turn street, voice guidance states an "at turn" message, which contains the same information as the near–turn message, except for the distance. This informs the driver that the maneuver is imminent.

When an upcoming maneuver is followed by another maneuver in very close proximity, the message for the first maneuver alerts the driver to prepare for the second one. An example is "Bear left to follow the correct branch of Sand Lake Road, then prepare to turn right." This aids the driver in positioning himself or herself correctly after the first maneuver, in order to be able to execute the second one. When the VOICE GUIDE function is switched off and back on again, a distance–appropriate guidance message is presented. In this way, the driver always has the ability to force the system to present an instruction for the next maneuver. The VOICE GUIDE function is automatically enabled at the start of a trip, as voice guidance was intended to reduce glances at the visual guidance display.

 

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