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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-RD-95-153
Date: November 1996

Development of Human Factors Guidelines for Advanced Traveler Information Systems and Commercial Vehicle Operations: Literature Review





When considering the implementation of new user–centered systems within an automobile, a number of issues must be addressed. According to Franzen and Ilhage (1990), these issues relate to driver mental workload, driver capacity, and the driving task analysis. Individual experiments have been accomplished worldwide, examining the implementation of in–vehicle systems in an environment where the user is already loaded with demanding tasks. These research findings often relate directly to the establishment of human factors guidelines for ITS. Researchers tend to study the differences in performance while using different systems or simulations. From this research, specific guidelines to support system design can be developed. In the following sections, specific research findings are reported in a format conducive to gleaning guideline material. Findings have been categorized based on the types of empirical studies reported and include driver information processing (i.e., attention and workload), visual display considerations (i.e., sensory and perceptual aspects), auditory display considerations, tactile displays, controls, user demographics, and user behavior and acceptance. While not all of the studies have findings that directly lead to guidelines, the majority are pertinent to future system design.

Driver Information Processing Demands: Attention and Workload

General Visual Display Considerations

Visual Information Display Research Specific to Navigation Systems

Auditory Display Considerations

Tactile Display Considerations

Manual Control Research

Driver Demographics

Driver Acceptance and Behavior

CVO–Specific Human Factors Research


Driver Information Processing Demands: Attention and Workload

The driving task does not require a constant level of attention demand since some driving conditions require more attention than others (Mourant and Rockwell, 1970). For example, two–lane streets require more attention than interstates; curved roads require more attention than straight roads; heavy traffic requires more attention than light traffic (Hulse and Dingus, 1989). Dingus and Hulse (1993) hypothesized that when the difficulty of the composite driving task exceeds the resources of the driver, no amount of expended effort will keep performance constant. At this point of overload, performance in driving (and ATIS–related tasks) begins to decline. Thus, it is important to keep driver attention below the point of overload.

The majority of the systems under development (or planned for the future) will be demanding enough to warrant the designation of tasks to be performed by the driver as "pre–drive" and "in–transit." "Pre–drive" consists of the complex planning and attention–demanding tasks. "In–transit" consists of a relatively small subset of tasks that are necessary for efficient system usage while the vehicle is in motion (Lunenfeld, 1990). Such a delineation is necessary due to the attention and information processing constraints present in the driving environment.

The in–transit functions should be limited to necessity and convenience. For example, the only functions that are required for navigation while the vehicle is in motion are those associated with point–by–point decisions while traveling from a current location to a destination. Proper selection and design of in–transit functions can allow successful navigation to destinations without substantial driving task interference (Dingus and Hulse, 1993).

With respect to valuable functions present while the vehicle is in motion, all efforts must be made to limit the functionality of the in–transit mode to those tasks that:

  • Do not significantly interfere with the driving task.
  • Have convenience benefits that outweigh the cost (i.e., required driver resources) of including the function.
  • Will be used relatively frequently.

Some navigation functions that meet these criteria include providing only necessary information (distance to next turn street, direction of next turn, and name of next turn street) and providing information regarding proximal traffic congestion or obstacles (Dingus and Hulse, 1993).

An option available to increase in–transit functionality without compromising driving safety is the allocation of functions to a "zero–speed" category (Carpenter et al., 1991). Zero speed refers to when the vehicle is stopped, but is still in "drive." The navigation system could allow a certain subset of functions (e.g., orientation information) to be accessed under these circumstances without concern for overload. However, once the vehicle is in motion again, the display and control configuration would return to its previous in–transit state.

Another argument for minimizing in–transit information is the problem of "out of the loop" loss of familiarity (Dingus and Hulse, 1993). Presently, the driver is required to obtain most information from the outside driving environment (i.e., street signs, stop lights, etc.). The more information readily accessible within the car, the less likely the driver will obtain the same information from the driving environment. Thus, any problem, deficiency, or inconsistency that requires the driver to shift attention to the driving environment will potentially result in delay and increased effort since the driver will have become accustomed to having the information provided within the vehicle. Thus, there is a tradeoff; the more powerful and informative the system, the more the driver will rely on it to provide information, rather than search the driving environment for it (Dingus and Hulse, 1993).

Attention demands

Inquiries into the driver's ability to perform the driving task arise with any addition or change in the task, such as those associated with in–car ATIS systems. It is important not to overload the driver at critical times during the driving task (Perel, Brewer, and Allen, 1990; Smiley, 1989; Walker, Alicandri, Sedney, and Roberts, 1991). Walker et al. (1991) reported that subjects using complex navigation devices drove more slowly than those using less complex devices. These effects were also more prevalent in older drivers (55 years and older) than in younger drivers. If the driver is traveling at a faster speed or on a less complex road (i.e., fewer curves), shorter viewing time of any display will be required as compared to traveling at a slower speed or on less complex turns (Senders, Kristofferson, Levison, Dietrich, and Ward, 1967). Dingus, Antin, Hulse, and Wierwille (1989); Plude and Hoyer (1985); and Madden (1990) also report that driving attention demands for older drivers are increased due to decreased capacity.

To limit attention demands, Smiley (1989) recommended that signs outside of the vehicle should contain no more than six key words if the content is to be remembered. Dingus et al. (1989) recommended that in–vehicle systems increase the proportion of time that critical information is available on a visual display and limit information that is not needed at a given time.

The ability to convey information to the user is important in the development of ITS systems. Incorrect display formats, styles, and colors can make the system all but unusable to the drivers. Studies have shown that certain types of warning symbols, signing material choices, and lighting conditions affect the user's perception of the importance of display information (Zwahlen, 1988; Zwahlen, Hu, Sunkara, and Duffus, 1991).

Visual attention is particularly important to assess in driving since most information is gathered visually by the driver (Rockwell, 1972). Despite the almost sole reliance of driving on the visual modality, between 30 percent and 50 percent of visual attention, in most circumstances, may be devoted to tasks other than driving (Hughes and Cole, 1986). It is the availability of this spare resource that makes the inclusion of in–transit visual display information feasible. Designers must make displayed information usable to drivers even under extenuating circumstances, since the visual attention required by the driving task can change drastically at any given time (e.g., including a curve, the presence of traffic, or a change in type of roadway) (Dingus and Hulse, 1993). Therefore, displayed information must be usable under the most demanding circumstances.

A visual display that requires frequent and lengthy glances may prevent adequate monitoring of the driving environment. In fact, research has shown that deviation from the roadway lane center increases with longer eye–off–the–road time (Zwahlen and DeBald, 1986).

It appears that the presentation of auditory navigation information is superior to visual presentation of information in many circumstances. A major advantage of auditory presentation is efficient allocation of information processing resources. Allocating supplemental tasks to the auditory modality (particularly in situations of high visual attentional demand) has the potential for making the composite task of driving easier and safer (Dingus and Hulse, 1993).

Cognitive attention is another attention demand. The driver may be concentrating on one thing while his/her eyes are directed toward something totally unrelated (Cohen, 1971). For example, the driver could be daydreaming, listening to the radio, or attending to an auditory display and not attending to the road. Therefore, if navigation information is presented to the driver aurally, it will require cognitive attention even though the driver's eyes are on the road.


Workload is a complex, multi–variate construct that is an important consideration for ATIS. As stated by Kantowitz (1992), the practical benefit of measuring driver workload is a means to assess safety. Workload overload will result in unsafe circumstances. Since safety cannot be proactively and directly measured in driving (i.e., without installing a system and measuring accidents), human factors professionals must rely on indirect measures such as workload assessment. Kantowitz (1992) discusses the application of workload techniques traditionally used for aircraft applications to driving heavy vehicles. A summary of existing driving workload research can be found in a report by Smiley (1989). According to Smiley, systems could be designed to automatically avoid overload. For example, if the cellular phone is in use, then the map details are reduced on a navigation display. Workload can also be reduced by programming the system's "smart cards" to determine user characteristics such as reaction time, age, experience, and so on. In this way, a support system could be tuned to the particular needs of each driver. Information should also be prioritized within the system to match the environment. For example, map information could be reduced when the driver is actually driving through an intersection. This allows the driver to devote full attention to the road at the appropriate time and not to the display.

An experiment conducted by Noy (1989) used the secondary task method of workload measurement to determine what effects added tasks and task complexity have on driving performance. This study showed that as visual tasks in automobiles increase, headway and speed control suffer and lane deviation increases. Each of these elements cannot be compromised since the safety costs are too great. Therefore, Noy recommended that workload testing must be conducted before allowing systems to be produced and used by the general public. A tool being developed in Japan may aid in the ease of this testing. Atsumi, Sugiura, and Kimura (1992) have developed a method of workload testing based upon heart rate analysis.




General Visual Display Considerations

Basic display characteristics

Information legibility, whether text or graphic, is a major design concern for automobile visual displays. A delineation of all appropriate display parameter options (e.g., resolution, luminance, contrast, color, glare protection) is a complex topic that is beyond the scope of this section. Actual guidelines for determining the proper color, contrast, and luminance levels to be used in CRT displays within vehicles can be found by using the formulas derived by Kimura, Sugira, Shinkia, and Nagai (1988). In addition, a number of legibility standards are in existence for visual displays, including those developed for aircraft applications (Boff and Lincoln, 1988). Several of these standards are reviewed for ATIS/CVO applicable design guidelines in the Conclusions section. Since the automobile has many of the same difficulties as the aircraft environment (e.g., glare), many of the same standards apply. However, note that the selection of an automotive display will be more constrained by cost and perhaps have limitations well below the state of the art.

There are minimum acceptable legibility standards that must be met or the display is unusable. It is critical that these minimum standards be met in spite of constraints for a given application. In addition, selecting display parameters is a problem, since viewing distance is limited due to the configuration constraints present for an automotive instrument panel. Driver constraints pose another problem. Older drivers with poorer visual acuity and/or bifocal lenses must be carefully considered during the specification of the display parameters. To overcome this combination of limitations, the display parameters must be optimized within practical control. For example, Carpenter et al. (1991) used a "special high–legibility font" in a color CRT application to ensure that drivers could glance at the display and grasp the required information as quickly as possible. Other design aspects that aid in legibility include the upright presentation of text information (even in map applications), maximizing luminance and/or color contrast under all circumstances, maximizing line widths to increase luminance (particularly on map displays), and minimizing the amount of displayed information, in general, to reduce search time (Dingus and Hulse, 1993).

Additional legibility design considerations include contrast, brightness, and character size. The greater the degree of contrast, the quicker the detection and identification time for any target (up to a point). The brightness of the instrumentation panel has been shown to have an effect on reading performance when character size is relatively small (1.5 and 2.5 mm) (Imbeau, Wierwille, Wolf, and Chun, 1989). Character size also plays an important role in response time. Imbeau et al. (1989) found that older drivers performed poorly when smaller character sizes were used. Schwartz (1988) suggested that further research must be considered on overall density and information grouping characteristics when evaluating displays where human performance is the paramount design criterion. Schaeffer and Campbell (1988) looked at vertical disparity of displays on performance accuracy. Vertical disparity ranging from 0 to 17.5 mrad did not show any effects on performance accuracy. However, large disparities did result in diplopia, double images, and possibly suppression of one of the visual images.

The use of color

Another basic visual display concern deals with the presence of color deficiency and color blindness. Approximately 8 percent of the male population have some degree of color deficiency or color blindness. It is, therefore, important in consumer product applications (including ATIS displays) to avoid reliance on color coding of critical information. Additional color issues include avoiding selected color combinations (Boff and Lincoln, 1988) (e.g., blue lines on a white background, since this combination causes the line to appear to "swim"). They also recommended using color coding of information sparingly, since too many colors create more information density and an increase in search time.

Brown (1991) found that color–highlighting techniques resulted in quicker and more accurate recognition of targets on a visual display. Although instrument panel color has been shown to have no significant effect on reading and driving performance (Imbeau et al., 1989), Brockman (1991) found that color on a computer–display screen can be distracting if used improperly. Brockman recommended several guidelines to avoid confusion when using color to code information. First, color codes should be used consistently. Colors from extreme ends of the color spectrum (i.e., red and blue) should not be put next to each other since doing so makes it difficult for the reader's eye to perceive a straight line. Second, familiar color coding, such as red for hot, should be used. Third, color alone should not be relied on to discriminate between items. Brockman recommends designing applications first in black and white, then adding color to provide additional information.

Display location

A major component of the driving task is scanning the environment and responding appropriately to unexpected events. Fortunately, humans are sensitive to peripheral movement. An object moving in the periphery often instantly gains attention. In fact, some human factors professionals believe that peripheral vision is as important as foveal vision for the task of driving (Dingus and Hulse, 1993).

Given the above considerations, the placement of an information display becomes critical. The information contained on even a well–designed display system will require a relatively large amount of visual attention. Therefore, if the display is placed far from the normal driving forward field of view, none of the driver's peripheral vision can be effectively used to detect unexpected movement in front of the vehicle. Increased switching time is another disadvantage of placing a display far away from the forward field of view. Typical driver visual monitoring behavior involves switching back and forth between the roadway and the display in question. Dingus, Antin, Hulse, and Wierwille (1990) found that while performing most automotive tasks, switching occurs every 1.0 to 1.5 s. The farther the display is away from the roadway, the longer switching takes, and the less time can be devoted to the roadway or the display (Weintraub, Haines, and Randle, 1985).

The position of a visual display was also studied by Popp and Farber (1991). It was found that a display positioned directly in front of the driver resulted in better driver performance than one mounted in a peripheral location. However, performance on a symbolic navigation presentation format was hardly affected due to the change in position, and results for peripheral location were still quite good. Tarriere, Hartemann, Sfez, Chaput, and Petit–Poilvert (1988) reviewed some ergonomic principles of in–vehicle environment design and agree that the CRT display should be near the center of the dashboard and not too far below horizontal. The paper suggested that the screen be mounted 15 degrees below horizontal, but should not exceed 30 degrees for optimal driver comfort.

According to the discussion above, the display should be placed as close to the forward field of view as is practical. The most desirable display locations are high on the instrument panel and near the area directly in front of the driver. There is, however, another automotive option that is currently just beginning to be explored: head–up displays (HUD's). Briziarelli and Allan (1989) tested the effect of a HUD speedometer on speeding behavior. Although no significant difference was found between a conventional speedometer and the HUD speedometer, most subjects (70 percent) felt that the HUD speedometer was easier to use and was more comfortable to read than a conventional speedometer. Subjects also reported being more aware of their speed when using the HUD speedometer. Campbell and Hershberger (1988) compared HUD and conventional displays in a simulator under different workloads. Under both low and high workload conditions, steering variability was less for drivers using a HUD display than for those using a conventional display (Campbell and Hershberger, 1988). Also, steering variability was minimized when the HUD was low and centered in the driver's horizontal field of view. In another simulator study, Green and Williams (1992) found that drivers had faster recognition times between a navigation display and the "true environment" outside the vehicle when the display was a HUD over a dash–mounted CRT.

Given the above arguments, a HUD providing navigation information on the windshield could be a good choice since it is the forward field of view. Besides the arguments described above, another advantage of a HUD (at least most HUD's) is that they are focused at (or near) infinity, thus eliminating (or reducing) the time required for the driver's eyes to adjust between the display and the roadway. However, a number of concerns have been raised by Dingus and Hulse (1993) about the use of HUD's:

  • Luminance may be a limiting factor in the automobile due to the presence of glare and stringent cost constraints. A HUD that was too dim and hard to read could be worse than an in–dash display.

  • Issues regarding display information density and distraction must be carefully addressed for HUD's and could result in a different set of problems.

  • Issues regarding the division of cognitive attention with HUD's. The fact that a driver is looking forward does not mean that roadway/traffic information is being processed. The importance of this division of attention to driving task performance has yet to be determined.




Visual Information Display Research Specific to Navigation Systems

There is significant research being conducted on the use of visual presentation information and appropriate formats for that information. As previously discussed, the navigational display information should be limited to only that which is absolutely necessary. When following a pre–specified route, Streeter (1985) recommended that the necessary information should consist of the next turn, how far away the turn is, which street to turn on, and which direction to turn. Streeter found that people who are familiar with an area prefer to be given the cross street of the next turn, whereas people who are unfamiliar with an area prefer to be given distance information.

In addition to proximal (i.e., next turn) route–following information, notice of upcoming obstacles or traffic congestion would also be beneficial. Such information could conceivably make the composite task of driving safer, given that it can be displayed without requiring substantial driver resources (Dingus and Hulse, 1993).

The use of traffic information was studied by Ayland and Bright (1991). The study shows that drivers wanted reasons for suggested route changes. If an in–vehicle system tells a driver to deviate from a normal path, or take an unfamiliar turn, the driver wants information about the reason for the change, such as "exit left, accident ahead." The same conclusions were made in the Bonsall and Joint (1991) report with regard to reasoning for route changes. This study pointed out the need for accurate information. It was found that drivers would rather follow their own "best" route perceptions than the system's, especially if the user has experienced a high rate of inaccurate information.

Information provided to the driver should be timely. Sufficient time must be allowed for the driver to respond to any information. The driver needs time to hear and/or see the information, decide whether it is relevant, and act upon it. An above–average human response time is required–most (i.e., 95 percent or 99 percent) of the drivers should have ample time to respond under most driving circumstances. The time required by the driver to process information and respond is dependent upon a number of factors, including the task and the type of display format selected, which is beyond the scope of this paper. A discussion of driver response time requirements can be found in several sources, including the National Highway Traffic Safety Administration (NHTSA) Driver Performance Data Book (1986).

The value of automatic route selection in navigation

Several research studies (e.g., Dingus, Antin, Hulse, and Wierwille, 1989) have tested systems that do not provide a route to a destination. These systems provide a current location, area streets, and a pre–selected destination. There are several technological advantages to these systems, including less complex data base requirements and no route–algorithm requirement. However, such systems require the driver to perform trip planning tasks in transit instead of pre–drive (Antin, Dingus, Hulse, and Wierwille, 1990). Almost invariably, the information displays for navigation information systems are (and probably will continue to be) quite small. Thus, a requirement for non–route systems is to provide "zoom–in," "zoom–out," and pan features, in conjunction with prioritized streets, to avoid unreasonably high screen information densities. A person could "zoom in" to a small–scale map (e.g., 0.4 km (0.25 mi)) and see a detailed view of all area streets. However, if one "zooms out" (e.g., to a 32.2–km (20–mi) scale), many of the secondary streets disappear to maintain a reasonable perspective. Therefore, it is often difficult to see all of the secondary streets along a route, particularly if the route is long. A person must zoom in/out and pan to various locations in order to plan a route prior to starting the drive. However, particularly for complex or long routes, it is difficult and time–consuming to plan a route like this. After inputting a desired destination, what generally happens is that people drive immediately and plan the route as they travel. This strategy increases the driver's attention demand, since pre–drive planning has now been allocated as an in–transit task (Antin et al., 1990). Therefore, Dingus, Antin, Hulse, and Wierwille (1988) recommended that a provision for route selection be provided as part of the navigation and information systems.

Another advantage to providing a route–selection algorithm as part of navigation system features is that many more options are available for information presentation. If no route is provided, an area map must be displayed to navigate accurately. If a route is provided, the navigation information can be displayed aurally and/or visually, textually or spatially, in a turn–by–turn graphic format or an entire route graphic format.

Information format trade–offs for navigation systems

There are many information presentation formats that are being considered for navigation systems. Driver navigation behavior is a key consideration in format selection. Schraagen (1990) suggested that map–based displays do not give the driver information in a needed form. Drivers need to look for street names, landmarks, and road signs on the map to make navigational decisions. Verbal instructions such as "turn right" or "follow signs with directions to Amsterdam" would be the most usable format for the driver. Maps should be used only as an additional information source, not as the sole navigational tool.

Bartram (1980) tested subjects on planning a bus route using a list or a map. The results showed that subjects who used a map had faster decision times than those using a list. Another study conducted by Wetherell (1979) found that after subjects studied a driving route, either using a map or a linear list of turns, those using a map made more errors while en route. Wetherell concluded that these findings could have been caused by two factors: (1) the spatial processing demands of driving, seeing, and orienting interfere with maintaining a mental map in working memory; and (2) subjects had a harder time maintaining a mental model of a map learned in a north–up orientation when approaching an intersection going east, west, or south. In a study conducted by Streeter, Vitello, and Wonsiewicz (1985), subjects who drove a route through neighborhoods using a route list (i.e., series of verbal directions) were faster and more accurate than those who drove using a customized map with the route highlighted. Popp and Farber (1991) found that symbolic presentation of route guidance information was superior to other visual presentation modes, such as text or maps. Symbolic presentation had the lowest driver workload rating and best traffic safety behavior. Green and Williams (1992) compared the viewing perspective of different navigation displays, using either a map like "plan view," a forward "perspective view," or a combination of the two in an "aerial view." Green and Williams found that drivers recognized the presented display as matching the environment outside the car when an "aerial view" was used. The map like "plan view" was a close second.

The studies above indicate that either symbolic guidance displays or textual lists are easier to use than maps while navigating to unknown destinations. Note, however, that maps provide additional information (e.g., orientation information such as cross streets) that textual lists do not. Therefore, whether a map, symbolic guidance screen, or list is selected should depend on the desired task and required information. One approach to in–vehicle information display is to visually provide the information to the driver either in a graphical or textual format, depending on preference (Lunenfeld, 1989).

Dudek (1979) reported that information display format and style can affect driver's processing time and information perception. Familiarity of messages, messages arranged proportionally within the horizontal and vertical dimensions, and optimal message lengths (i.e., less than eight words for high speeds) have been shown to permit appropriate processing times for drivers. Drivers' familiarity with the locality and perception of such vague terms as "congestion" can affect the drivers' perception of the en route guidance system information. When dealing with local drivers, particularly commuters, studies have shown that drivers want to know the location of cross streets or landmarks; while non–local drivers prefer distances (Dudek, 1979).

Regardless of format type, an information display must be designed such that all in–vehicle information can be received in short glances and displays must not distract the driver (i.e., Lunenfeld, 1989). It is clear that less attention will be required for a well–designed turn–by–turn visual display format than for a full–route format. Little information is required for a graphic turn–by–turn screen, including only direction of turn, distance to turn, and turn–street name. Such information can be easily displayed in a legible, low attention–demanding format. McGranaghan, Mark, and Gould (1987) have characterized route following as a series of "view–action" pairs. A view–action pair refers to the sequential set of requirements where information is required for an upcoming event (i.e., turn), the event is executed, or the information for the next event is displayed. McGranaghan and his associates believe that only the information for the next view–action pair should be displayed for route following. In their view, any additional information is "extraneous" and "potentially disruptive" to the route–following task.

However, there are advantages to providing an entire–route display. One advantage is route preview. In circumstances of required low driving–task attention, the driver has the option to plan upcoming maneuvers in advance. While it is feasible and reasonable that pre–planning could alleviate the need for in–transit preview (i.e., map shown while the car is stopped, turn–by–turn configuration when the car is in motion), for complex routes, preview information may be valuable to recall and plan for upcoming maneuvers (Dingus and Hulse, 1993).

Route information provides a second advantage during circumstances of close proximity maneuvers. Many circumstances exist in the driving environment for which two (or more) quick turns are required. In the turn–by–turn symbolic screen case, the information for the second turn may come up too soon (and under circumstances where attention is needed for driving) to comfortably execute the second maneuver. In the route–map case, such an event can be planned in advance (Dingus and Hulse, 1993).

A trade–off must be made when selecting a route–map display format as to whether or not the map should be presented "heading up" (i.e., the direction that the vehicle is traveling is always up on the display) or "north up." The most significant issue regarding heading up versus north up is the speed and accuracy with which the displayed information is interpreted by the driver. With a north–up orientation, the driver must often mentally rotate the map image (e.g., if the heading is southeast) to determine whether to turn right or left. This additional operation requires additional attention and processing time and results in more errors for the population as a whole (Dingus and Hulse, 1993).

One advantage to north–up map presentations is that they do not "move" (Dingus and Hulse, 1993). For a heading–up format, the map must constantly rotate as the vehicle heading changes to maintain heading–up. This rotation, particularly when presented in the visual periphery, can be somewhat distracting. Antin et al. (1990) found that driver visual scanning behavior was adversely affected by a moving–map system. The authors stated that the novelty of the display (the subjects were novices and therefore interested in the display) had the effect of pulling spare driver resources toward the display. However, other factors, such as distraction induced by movement in the periphery, probably contributed to this finding. It should be noted, however, that a study by Hulse (1988) indicated that although visual scanning patterns are affected by the introduction of a moving–map system into the automobile, drivers can adapt their visual scanning behavior to account for changes in driving–task attention demand when required. Hulse found that the probability of a glance to the roadway center increased from 0.51 in light traffic conditions to 0.61 in heavy traffic conditions. Therefore, while some degree of distraction occurs because of these displays, apparently drivers are able to ignore it (at least to some extent) if required by the driving situation.

In a study of the ETAK Navigator, Antin et al. (1990) found that it took, on–average, approximately twice as long to plan a route using a paper map. They also noted that a moving–map display was more intrusive to driving behavior than the paper map, but it was still within driver capabilities. Several studies evaluating the general effectiveness of in–vehicle information systems have been reported (Al–Deek and Kanafani, 1989; Dingus et al., 1988; Dingus, Hulse, Krage, Szczublewski, and Berry, 1991; King, 1985; Lineberry and Martin, 1990; van Vuren and Watling, 1991).




Auditory Display Considerations

Auditory information, including voice–based systems, is an alternative medium to visual information display. Turnage and Hawthorne (1984) found that drivers did not respond as well to synthesized speech as to natural speech. Thomas, Gilson, Ziulkowski, and Gibbons (1989) found that the processing of synthetic speech can produce increased demands on the short–term memory as compared to human speech. They noted that the performance decrements observed were attributed to memory capacity and not to misperception of synthetic speech. Davis and Schmandt (1989) also reported that driving instructions are more helpful when modeled after natural language. The Back–Seat Driver system (Davis and Schmandt, 1989) and the DIRECT system (Gilbert, DeFrain, and Underwood, 1991) have examined the use of voice–based in–vehicle information systems.

Walker et al. (1991) reported that drivers using auditory navigation devices drove more safely than those using visual devices. Subjects using visual devices missed more gauge changes, had longer reaction times, and drove more slowly than subjects using auditory devices. Presenting the same information both aurally and visually was also suggested.

Additional research assessed the workload differences between visual and auditory information. Labiale (1990) found that workload is lower when using auditory presentation of navigation information as opposed to a visual presentation. This study also showed that drivers preferred auditory information because they felt it was a safer system.

Despite the apparent advantages of voice systems over visual displays for in–vehicle applications, Dingus and Hulse (1993) pointed out that aural information may not be a panacea for attention and workload concerns. The workload required to process auditory messages increases as the intelligibility of those messages decreases. Low–cost systems will be required for automotive navigation systems due to marketing considerations. This cost constraint requires the selection of digitized speech that does not provide any street name information to the driver (due to data–base constraints) or synthesized speech that is less intelligible than digitized speech. Although the quality of low–cost synthesized speech is constantly improving, factors such as tonal quality and inflection limit its relative effectiveness (Sanders and McCormick, 1987).

Even though numerous research studies have been conducted testing forms of synthesized speech, the state–of–the–art technology is not yet to the point where intelligibility/

comprehensibility can be predicted in all situations or environments. However, it is known that a number of factors influence intelligibility, including speech rate, message length, message content, message complexity, background noise, pitch, and loudness (Van Cott and Kincade, 1972; Marics and Williges, 1988).

Background noise is an intelligibility factor that is particularly important in an automobile and affects both digitized and synthesized speech. Noise in an automobile sometimes reaches 90 dB (A), making voice intelligibility virtually impossible in some circumstances (Bailey, 1982). The noise in an automobile also comes from many sources with different masking properties (e.g., citizens band (CB) radio, cellular telephones, stereo systems, conversation, and road noise), making alleviation of the noise problem somewhat difficult. Although hearing is not a primary sensory mode for driving, there are situations when in–vehicle auditory displays could mask other important signals (i.e., railroad grade crossings or emergency vehicles on the road) (Lunenfeld, 1990). Therefore, in such situations, the loudness and frequency components, and the spectral content of the voice would have to be carefully considered.

In addressing some of the intelligibility concerns discussed above, Labiale (1990) recommended that the amount of aural information presented be restricted (seven to nine bits) or the aural cue be used as a prompt for a simple visual guidance presentation. Also recommended is the ability to repeat the aural message, especially if information is complex, to aid in intelligibility and recall.

A driver's prioritization of a voice message is an additional and potentially negative issue related to the presentation of aural commands. A study conducted by a Japanese automobile manufacturer indicated that drivers apparently respond instinctively to verbal information to a greater degree than visual information. This behavior was manifested in a tendency to follow the in–vehicle instructions even if they conflicted with traffic regulatory information (e.g., turning the wrong way onto a one–way street) (Noy, 1991).

Although voice presentation can alleviate visual attention–demand problems associated with navigation information, it is not without problems. Dingus and Hulse (1993) recommended that the auditory modality be used to: (1) provide an auditory prompt (e.g., a tone) to signal the driver to look at a visual display for changing or upcoming information (thus lessening the need for the driver to constantly scan the visual display in preparation for an upcoming event), or (2) have some type of simple visual information presentation to supplement the auditory message (so that a message that is not fully understood or remembered can be checked, or later referred to, via the visual display).




Tactile Display Research

There are some methods of information presentation that can be used to bypass the use of visual and auditory information. Janssen and Nilsson (1990) conducted a simulator study looking at the different methods of presentation for a collision warning system. They investigated auditory, visual, and tactile warnings. A system that gave tactile feedback seemed to be a unique concept. The experiment was a simulator study that used a "smart" gas pedal that would pulsate if the driver was to get too close to the car in front. This method of information presentation could be compared to a visual light or an audible buzzer. The warning systems that used lights or buzzers showed increased negative behavior that could prove to be dangerous. Negative behavior was defined as an increase in driving speed, increase in acceleration and deceleration levels, and an increase in left–lane driving (passing behavior). Janssen and Nilsson (1990) found that the "smart" gas pedal suffered none of these negative side effects and reduced following distance.

Nilsson, Alm, and Janssen (1991) continued this research to look at driver reaction to intervention factors using the "smart" gas pedal. Three conditions were compared to evaluate the level of vehicle intervention a driver would find unobtrusive. A "warned" subject would receive only the vibration of the pedal if they were to follow another vehicle too closely. A driver in the "suggested" condition would feel resistance on the gas pedal, but could override the resistance by applying more pressure. The final condition was that of "intervention," where the "smart" pedal would automatically slow the car to a 4–s following distance. While the "intervention" was the safest with regard to behavior, it was met with the least acceptance; drivers preferred the "warned" and "suggested" systems.

The above described research could potentially have implications for IVSAWS applications.




Manual Control Research

Many control–related technological advancements are available for use with computers and, therefore, are available for potential use as part of ATIS and CVO systems. Sears and Shneiderman (1991) found no performance differences between the mouse and touchscreen for targets ranging from 32 to 4 pixels per side. Stabilization of touchscreens reduced error rate for smaller character size.

The trade–off between "hard" buttons and "soft" CRT touchscreen push buttons has become a concern of the ITS human factors community (Dingus and Hulse, 1993). With the use of CRT's and flat–panel automobile displays, there has been a strong temptation to use touchscreen overlays for control activation. While this can be a good method of automobile control for pre–drive or zero–speed cases, research has shown that this is not true for in–transit circumstances. Zwahlen, Adams, and DeBald (1987) looked at safety aspects of CRT touch–panel controls in automobiles as a function of lateral displacement of the centerline. This study found an unacceptable increase in lateral lane deviation with the use of touch–panel controls. This study found the touchscreen control panels visually demanding, as demonstrated by the relatively high probabilities of lane deviations. Zwahlen et al. (1987) suggested that use of touch–panel controls in automobiles should be reconsidered and delayed until more research with regard to driver information acquisition, information processing, eye–hand–finger coordination, touch accuracy, control actions, and safety aspects has been conducted and the designs and applications have been improved to allow safe operation during driving.

Monty (1984) found that the use of touchscreen keys while driving required greater visual glance time and resulted in greater driving and system task errors than conventional "hard" buttons. There are two reasons for this performance decrement: (1) the controls are non–dedicated (i.e., change depending on the screen), and (2) soft keys do not provide tactual feedback. For a "hard" button, the driver must (depending on the control and its proximity) glance briefly at the control and then find the control using tactile information to accomplish location "fine–tuning." For the soft keys, the driver must glance once to determine the location, and glance again to perform the location "fine–tuning" (Dingus and Hulse, 1993).

One way to minimize control use while in transit is to severely limit control access. Therefore, as with the display information previously discussed, it is important to assess the necessity of every control in terms of both in–transit requirements and frequency of in–transit use to minimize driver control access. Those controls that are not absolutely necessary for the in–transit environment can then be allocated to pre–drive or zero–speed circumstances (Dingus and Hulse, 1993).

Control location has been shown to be important in automotive research. The farther a control is located from the driver, the greater the resources needed to activate the control. This has been demonstrated by Bhise, Forbes, and Farber (1986) and Mourant, Herman, and Moussa–Hamouda (1980), who found that the probability of looking at a control increased with increased distance. Therefore, controls present on the steering wheel, or otherwise in close proximity to the driver, are easier to use.

Control activation complexity and steering interference have also been shown to be important issues. Monty (1984) has shown that continuous controls or controls requiring multiple activations are significantly more difficult to operate. Therefore, limiting controls to single, discrete activations provides fewer resource requirements.




Driver Demographics

The older driver

The most prevalent user demographic issue is driver aging. Parviainen, Atkinson, and Young (1991) studied both the aging population and the handicapped with regard to in–vehicle systems development. Parviainen et al. (1991) stated that the number of aging drivers will double by the year 2030, and that systems must be designed to accommodate these special populations. According to Franzen and Ilhage (1990), the driver population over age 65 will soon consist of one out of every seven drivers on the road. Older drivers constitute the most rapidly growing segment of the driving population in number of drivers licensed, distance driven, and proportion of the driving population. However, there continues to be problems associated with an aging driver population, including discrimination and lack of highway traffic engineering to accommodate older drivers (Waller, 1991).

Research has shown that older drivers spend significantly more time looking at navigation displays than younger drivers (Pauzie, Martin–Lamellet, and Trauchessec, 1991; Dingus, et al., 1989). Experiments comparing the visual glance frequencies of both elderly and young drivers toward a CRT screen with navigation information were conducted. It was found that younger drivers spent 3.5 percent of the driving time looking at the display, while elderly drivers spent 6.3 percent of the time looking at the display. Consequently, when navigation systems are involved, this group devotes less time directed toward the roadway. This dictates that special consideration must be given to this segment of the population, and that minimizing in design of a navigational information display glance time is critically important.

Older drivers perception of risk is increasing (Winter, 1988). Winter suggested that more older drivers are "running scared," frightened away from traffic situations they can probably handle, as well as those they cannot. Psychologically, some of them experience fear and anxiety about their vulnerability in a fast, complex traffic world, and in relation to citations, insurance, and licensing examinations. Winter suggested that older drivers may develop compensatory attitudes and behaviors, some of which are positive and contribute to safety and some of which are negative and promote unsafe practices. On the positive side, they become more responsible and law–abiding. However, older drivers may deny that their skills are decreasing and continue to drive under conditions highly unsafe for them. Winter reasoned that a prime factor in elderly attitude toward driving is the fear of an accident or a violation that would lead to reexamination for licensure and end in a possible loss of both the license and of the independence it affords. Another threat is the cancellation of insurance or the rise in premiums that would make driving too costly.

Many traffic engineering controls designed for older drivers have been suggested in recent research. Lerner and Ratté (1991) suggested that older drivers have a need for advanced signing of upcoming exits. According to Bishu, Foster, and McCoy (1991), older drivers favor larger signs, lower speed limits, and more stop signs and traffic signals. Garber and Srinivasan (1991a) suggested that an increase in amber time or the protected phase for left–turn lanes would help reduce the large percentage of involvement in left–turn lane accidents by elderly drivers.

Research has indicated the existence of many age–related performance problems. Walker, Alicandri, Sedney, and Roberts (1990) found that older drivers (55 years of age and older) drove slower, had larger variability in lateral placement, had longer reaction times to instruments, were more likely to be in another lane after a turn, and were more likely to make navigational errors compared to middle–aged drivers (35 to 40 years of age) and younger drivers (20 to 25 years of age). Women appear to be at risk from age–related changes in cognitive functioning, particularly those with less driving experience and after 75 years of age. Men appear to be at risk for both accidents and citations as a result of sensory and psychomotor function problems. However, there are no significant differences in the rates at which males and females reported either accidents or citations (Bishu et al., 1991; Laux, 1991). For drivers over age 74, slowing of reaction time has a strong association with overall driving performance and with specific driving measures, especially those related to vehicle control (Ranney, 1989). However, Olson and Sivak (1986) found that older drivers, ages 50 to 84, had relatively the same perception–response time to unexpected roadway hazards as younger drivers, ages 18 to 40. Further research in this area has been reported by Chang, 1991; Greatorex, 1991; Ranney and Pulling, 1990; Reynolds, 1991; Stelmach and Nahom, 1992; Vercruyssen, Carlton, and Diggles–Buckles, 1989.

Several studies have been conducted to determine the driving habits, safety, and accident rates of older drivers (Evans, 1988, 1991; Garber and Srinivasan, 1991a, 1991b; Jette and Branch, 1992; Kostyniuk and Kitamura, 1987; McKelvey and Stamatiadis, 1989). Evans reports that although accident rates for drivers 65 years old is greater than that for drivers who are 40 years old, both groups have substantially lower accident rates than for drivers at age 20.

Why grandpa wears glasses

It is generally acknowledged that vision plays a vital role in safe and proficient driving (Kosnik, Sekuler, and Kline, 1990). However, the aging process does bring about a variety of changes in drivers' visual functions and their cognition, which may gradually affect their interaction with vehicle environment. Older drivers report problems with visual processing speed, visual search, light sensitivity, and near vision (Kosnik et al., 1990). Older drivers reported a higher frequency of visual problems, but generally do not have unusual visual problems.

Research has shown that older drivers' visual performance improves with the use of specific display characteristics. Babbitt–Kline, Ghali, and Kline (1990) reported that the use of icons improves user visibility in both distance and lighting conditions (e.g., daylight versus dusk). Hayes, Kurokawa, and Wierwille (1989) reported that many performance problems in viewing visual displays can be eliminated by increasing the character size of textual labels. Yanik (1989) observed that for color displays, drivers had better visual responses to yellows, oranges, yellow–greens, and whites on contrasting backgrounds. Yanik also found that analog displays (i.e., moving pointer) were preferred over digital or numerical displays. Other studies involving older drivers' visual abilities are reported by Mortimer (1989); Ranney and Simmons (1992); and Staplin and Lyles (1991).

Designing for the older driver

Designers of transportation systems will have to consider the needs of older drivers. Mast (1991) stressed a greater need for transportation system research and development for older drivers in areas of traffic control devices, changeable message signs, symbol signing, hazard markers, night driving, sign visibility, intersection design, traffic maneuvers, left turns against traffic, and merging/weaving maneuvers.

Lerner and Ratté (1991) reported that focus groups identified the following needs and generated ideas and countermeasures for the safe use of freeways by older drivers:

  • Lane restrictions, time restrictions, separate truck roadways, and other methods to reduce interaction with heavy trucks.

  • Greater police enforcement, new enforcement technologies such as photo radar, new traffic control technologies, and other methods to reduce speed variability in the traffic stream.

  • Better graphics, greater use of sign panels listing several upcoming exits, and other methods to improve advance signing so that it better meets the visual and information needs of the elderly.

  • Wide high–quality shoulders, increased patrol, brightly lit roadside emergency phones, promotion of citizens band radio use, better night lighting, more frequent path confirmation, and other methods to overcome concerns about personal security.

  • More legible maps, map–use training in older–driver education courses, in–vehicle guidance systems, and other pre–trip planning aids that are designed to be used by older drivers.

  • Appreciation for the safety benefits, on–road "refresher" training for those who have not used high–speed roads recently, training in recovery from navigational errors, and other older–driver education specific to freeway use.

  • Eliminating short merge areas and other methods to improve the interchange geometries that the focus groups identified as contributing to anxiety.

Learning and training effects

Groeger (1991) discussed the learning process of the driving task and a proposed intelligent vehicle system that could continue to teach drivers as their skills mature or deteriorate. The Personalized Support and Learning Module (PSALM) is a concept derived as part of the DRIVE project. It would use the sensors in many ITS–equipped automobiles to monitor driver performance. Individualized and task–specific instruction will be possible with PSALM.

Fatigue effects

Another topic addressed in the new vehicle technology research is fatigue detection. Systems are being developed that measure driver performance through steering wheel input by the driver. If patterns suggesting fatigue are recorded, then audible alarms awaken the driver or suggest taking a rest break. Several research studies and specific systems are discussed in Tarriere, Hartmann, Sfez, Chaput, and Petit–Poilvert (1988). A similar Japanese system was developed by Nissan and is discussed in detail in the report by Senoo, Kataoka, and Seko (1984). These systems could be considered ATIS.




Driver Acceptance and Behavior

Acceptance research

When developing components of ITS, it is important to consider the attitudes of system users. Is the system acceptable, usable, and affordable? A good review of the issues associated with ITS acceptance is presented by Sheridan (1991). Lunenfeld and Stephens (1991) also discussed the specific issues of night–vision enhancement systems.

A survey by Marans and Yoakam (1991) found that most commuters felt that ITS was a plausible solution to traffic congestion. The highest approval of ITS (48 percent) came from commuters whose work commute was from suburban to suburban localities. The survey also reported that 86 percent of the commuters drove their own car to work.

A UMTRI focus group study (Green and Brand, 1992) elicited attitudes on 11 types of in–vehicle electronics. Drivers were cautious about the navigation systems. Most indicated that the systems were good for someone else to use, in certain situations. It was noted that men preferred maps and women preferred directions. Both genders preferred left/right turning directions rather than compass north/south.

A survey by King (1986) analyzed self–reported navigation and map–reading skills. King found that 27.6 percent of all travel represented non–familiar trips, and that the majority of respondents felt confident in their own navigation and map–reading skills.

In a survey by Barfield, Haselkorn, Spyridakis, and Conquest (1989) (see also Haselkorn, Barfield, Spyridakis, and Conquest, 1989 and 1990; Haselkorn and Barfield, 1990; Spyridakis, Barfield, Conquest, Haselkorn, and Isakson, 1991; Wenger, Spyridakis, Haselkorn, Barfield, and Conquest, 1990), commuters rated commercial radio as the most useful and preferred medium from which to receive traffic information both before and while driving, as compared to variable message signs, highway advisory radio, commercial TV, and telephone hotline systems. Commuters also indicated that departure time and route choices were the most flexible commuter decisions. Most commuters indicated that they could not be influenced to change their transportation mode.

Driver acceptance of technology was assessed by McGehee, Dingus, and Horowitz (1992) while studying a front–to–rear–end collision warning system. They reported that drivers often follow at distances that are closer than brake reaction time permits for accident avoidance. This close driving behavior may be due to the lack of previous bad experiences. A front–to–rear–end collision warning system (whether it is visual, aural, or a combination of both) had the potential of providing added driver safety and situation awareness and was generally accepted as a worthwhile device by the subjects tested. According to a study by Erlichman (1992), subjects showed a preference for text– and voice–warning message systems that were demonstrated in a study on safety advisory and warning system design. The results of these studies apply to IVSAWS.

Route selection and route diversion

A major component of ITS systems includes navigation aides. These devices can provide the user with current traffic conditions, alternate route selections, and guidance over the alternate routes. The effectiveness of these systems in alleviating traffic congestion has been reported in studies by Dingus and Hulse (1993); Halati and Boyce (1991); Hamerslag and van Berkum (1991); and Knapp, Peters, and Gordon (1973).

Drivers have been shown to resist diverting from their present route to avoid congestion (Dudek, 1979). Dudek showed that 50 percent of drivers were willing to avoid a 20–min delay, but only 8 percent were willing to avoid a 5–min delay. According to this report, congestion would have to be moderately severe before people divert. This may be due to lack of information known by the driver. A key to persuading drivers to use an alternate route is appropriate and timely information. For example, if drivers know they can save time by using an alternate route, but do not know how much time, the drivers may be hesitant to change routes. In addition, drivers tend not to take the shortest or fastest route if it is less pleasant. Cross and McGrath (1977) found that drivers select routes based on the following factors: efficiency (fastest route 54 percent, shortest route 53 percent), problem avoidance (safest route 43 percent, more familiar with route 36 percent), more miles of multiple lanes (31 percent), roads in better condition (30 percent), less chance of getting lost (24 percent), less traffic (18 percent), and pleasure and personal convenience (most scenic route 25 percent). Factors such as road quality, number of junctions, and average speed are also important in route selection. Streeter and Vitello (1986) had 33 women rate what was most important to them in terms of navigational preferences. For short trips, they wanted to avoid road construction/bad roads and traffic. For long trips, they also wanted to avoid road construction/bad roads. Other areas that were important to the drivers for long trips were use of major roads, scenery, few stoplights, and travel time.

Allen, Stein, Rosenthal, Ziedman, Torres, and Halati (1991) looked at driver route diversion and alternate route selection using in–vehicle navigational systems. Overall, the study showed that navigation system characteristics can have a significant effect on driver diversion behavior, with better systems providing more accurate traffic congestion information. Navigation systems equipped with congestion monitors effectively changed driver behavior; however, not all drivers exited to the alternate route suggested by the computer. Older drivers (55 years of age or older) were more reluctant to choose alternate routes.

Research has shown that drivers have difficulty planning optimum routes from their origin to their destination (King and Rathi, 1987). These travel inefficiencies lengthen travel time. King and Rathi asked subjects to plan three relatively long trips in unfamiliar areas by using only a road atlas. The routes selected by the subjects were compared with the routes recommended by the American Automobile Association (AAA) for both distance and approximate driving time. Analyses of the data indicated that the routes selected by the subjects on average increased trip length by 12.1 percent.

Tong, Mahmassani, and Chang (1987) found that commuters combine their last experienced travel time with the supplied travel time to predict travel time for their next trip. When commuting to work, this value was adjusted by a margin that was governed by the last experienced schedule delay in order to protect against an unacceptably late or early arrival time. Tong et al. (1987) noted that additional information supplied to commuters reduces the importance of relying on their memory or accumulated experience in the prediction of travel time.

Shirazi, Anderson, and Stesney (1988) studied commuters' attitudes toward traffic information systems and route diversion. Overall, commuters wanted timely and accurate information, more frequent reporting, and better uses of electronic freeway message signs. Most were in favor of continuous radio traffic reporting (68 percent) and traffic information phone numbers (53 percent). In general, males were more likely to change routes than females. Females (38 percent) were less likely to know alternative routes than males (62 percent). Drivers commuting for short periods (less than 45 min) were more likely to change routes to work than those with longer travel time. Nearly 70 percent of commuters said they would leave the freeway if more accurate information regarding their commute was available, and if they knew that surface streets offered a shorter route to work. The most frequently cited factor for route change was radio traffic reports (30 percent), followed by personal experience (20 percent).

Khattak, Schofer, and Koppelman (1991) found that most commuters changed their routes based on radio traffic reports. Khattak et al. (1991) also found that commuters used traffic information more when they were en route, compared to when they were planning their trips. Drivers reported a preference for information on near–term prediction of traffic conditions for congested and unreliable routes as opposed to current traffic conditions. Drivers considered current conditions as unstable with the potential for rapid change. Overall, radio traffic reports were attributed to reducing en route anxiety and frustration of drivers even if drivers did not modify their trip decisions. Commuters who are more likely to change their departure time in comparison to their route selection wanted long–term prediction of traffic conditions.

Barfield et al. (1989) (see also Haselkorn et al., 1989 and 1990; Haselkorn and Barfield, 1990; Spyridakis et al., 1991) used cluster analysis to show that four commuter subgroups exist with respect to their willingness to respond to the delivery of real–time traffic information:

  • Route changers, those willing to change routes on or before entering Interstate 5 (20.6 percent).
  • Non–changers, those unwilling to change time, route, or mode (23.4 percent).
  • Time and route changers (40.1 percent).
  • Pre–trip changers, those willing to change time, mode, or route before leaving the house (15.9 percent).

Bonsall and Parry (1991) tested drivers' compliance with route guidance advice by asking subjects to make several "journeys" from specified origins to specified destinations using an IBM computer–based simulator, Interactive Guidance on Routes (IGOR). The quality of the advice IGOR provided varied. Overall, about 70 percent of the advice was accepted. Acceptance declined as the quality of advice decreased. Participants' perception of the advice was dependent upon the physical layout of the network. Generally, if previous advice had been very good, then even bad advice was likely to be accepted; and if previous advice had been very bad, then a bad item of advice was almost certain to be rejected. Acceptance of advice generally decreased as familiarity with the network increased. Visible presence of traffic congestion or a road sign apparently confirming advice increased acceptance of advice. Women were found to be significantly more likely to accept advice, particularly non–optimal advice, than were men. Subjects who normally had high commuting distances were less likely to accept advice.

To analyze the effectiveness of route–guidance systems, Abu–Eisheh and Mannering (1987) developed a route and departure time choice modeling system where departure–time was a continuous variable. The models were estimated using a sample of people commuting to work, and the resulting coefficient estimates were significant. This study also found that males have a tendency to drive faster than females, that safety belt users tend to drive faster, and that younger commuters drive faster than older commuters.

Alcohol impairment

Alcohol impairment needs to be considered in the design of ATIS/CVO systems since about half of all fatal accidents involve drunk drivers. The use of alcohol is believed to cause 25,000 deaths a year on U.S. highways. A recent study by Zador (1991) estimated that a driver nearly doubles the risk of being in a fatal, single–car crash with each increase of 0.02 in the blood alcohol concentration (BAC). The risk is higher for younger drivers than for older drivers, and females had higher relative risk than males. At higher BAC's (at or above 0.15 BAC), the risk of crashing was 300 to 600 times the risk at zero or near–zero BAC's.

Alcohol has many documented effects on the human body (Meier, 1990). Studies have suggested that subjects tend to ignore instructions and traffic rules after drinking (Linnoila and Mattila, 1973). A study by Farrimond (1991) suggested that alcohol affects visual constancy values. Subjects saw familiar objects as larger than actual size and saw hazards as smaller and farther away than they actually were. According to a study by Moskowitz, Burns, and Williams (1985), skilled tasks were impaired at low BAC's. These impairments lead to accident–causing driver errors.

A recent study by Holubowycz, McLean, and McCaul (1991), conducted in Australia, suggested that there are two to three times as many drivers on the road who were over the legal BAC limit than previously believed by police data. However, in a study by Lund and Wolfe (1991), data indicate that the incidence of alcohol–impaired driving on weekend nights fell by one–third or more in the United States between 1973 and 1986, and that the decline affected most population subgroups. This study attributes the decline to an increase in public awareness brought about by such national groups as Mothers Against Drunk Driving (MADD).




CVO-Specific Human Factors Research

Acceptance research

Several major surveys addressing the use and acceptability of advanced technology have been performed using CVO's as respondents. The results of these surveys are summarized below.

A Survey of the Use of Six Computing and Communications Technologies in Urban Trucking Operations. A survey performed by the American Trucking Association (Willis, 1992) was conducted on the use of six kinds of advanced telecommunications and commuting technologies by truck operators in urban areas. The technologies investigated were computer–aided dispatch (CAD), two–way text communication, AVL, in–vehicle navigation, AVI, and traffic information services. A total of 69 companies were surveyed.

The results showed that 35 out of 69 firms used CAD. Two–thirds of those that used CAD employed dynamic routing (i.e., rerouting of vehicles in response to changing patterns of demand during the day).

Two–way communication was the second most widely used technology (21 companies). The survey found that two–way text communication is viewed as having both safety and operational advantages over voice communication. For example, text messages can be stored until it is safe for the driver to assess them.

Automatic vehicle location is ranked third and was being employed by 15 of the 69 companies. Management and dispatchers liked AVL as a means of better managing drivers and vehicles. Drivers' views were mixed or negative. Thus, drivers' needs must be addressed in order for AVL to work.

The survey found that in–vehicle navigation systems are seldom used by truck operations. Such systems are used more often by fire departments and ambulance services (5 out of 69 companies).

The AVI results were not as useful since most of the surveyed users were participating in an AVI toll collection study. However, those subjects using AVI were pleased with the technology.

Fleet management is the key task that ITS offers to streamline for both commercial carriers and public transit. As with ATIS for private vehicles, improved routing and communications will be key components for fleet management. Regulatory compliance is also promising. Operational field tests involving many State agencies are currently under way, such as Heavy–vehicle Electronic License Plate (HELP) program and Advantage I–75.

Institutional Barriers and Opportunities for IVHS in Commercial Vehicle Operations: An Iowa Case Study (Midwest Transportation Center, 1992). This survey of commercial vehicle operators was undertaken to determine the most feasible and desirable ITS features for CVO applications. The following are summarized results of this survey.

The most promising CVO applications are:

  • Weigh–in–motion using AVI.
  • Pre–clearance for safety inspections.
  • "One–stop shopping" compliance with all truck regulations at a central place.
  • Electronic toll and traffic management.
  • Automated apportioned fuel tax administration.
  • Audits of apportioned fuel tax.

Other promising applications include:

  • Hazardous materials identification.
  • Navigation aids due to cost.

Survey of the Trucking Industry's Preferences for IVHS (Stone and Ervin, 1990). This survey of commercial truck drivers reported the following findings:

  • Seventy percent of the sample preferred a two–way conversation link for communicating instructions and messages.
  • Current users of advanced technology rated text messages equal in value to the conversation link.
  • Larger carriers rated AVI for WIM higher than the smaller carriers did.
  • Warning and control systems were rated highly. Sixty–five percent of the sample rated impending rollover warning as "very important." Seventy–nine percent rated collision warning as "very important." Overwhelming interest was seen in "mayday" alert systems.
  • Rural carriers preferred video maps for routing.
  • Urban carriers rated voice routing and video routing as equal in value.
  • Urban carrier dispatchers preferred electronic map presentation of vehicle location, whereas rural dispatchers thought text and map were equally desirable.
  • Truck location updates should be accomplished every 1 to 4 h.

The TRANSCOM project (described in the previous section) reported the following results:

  • Real–time traffic incident notifications were valuable to trucking companies. The participating companies stated that the information helped them to avoid incidents, thus saving time.
  • Dispatchers had a very hectic job and were often too busy to relay information to drivers.
  • Those drivers with limited route options did not always benefit from real–time incident information.
  • Incident notification was most valuable when sent only to those drivers affected by the incident. Receiving information on every incident in the area caused many firms to ignore their pagers used for notifications since it provided information that typically did not affect them.
  • A good indicator for judging the usefulness of a feature was the time value placed on the commodity and the ability to use alternate routes. It was recommended not to judge the usefulness of the indicator based on the type of carrier.
  • A weekly traffic and transit advisory of lane closings and major traffic–generating events was beneficial to all truckers for planning routes.
  • Two–way communications between drivers and dispatchers on how to enhance the pager's usefulness was not necessary, but it helped.

HELP and Crescent Demonstration project. The HELP program involved the use of AVI, WIM, AVC, satellite data links, and data communication networks, including on–board computers. This research is intended to design and test the integration of selected technologies, including AVI, AVC, and WIM equipment, computer integration, and communication linkages.

The program involves 14 U.S. States, a Canadian Province, a U.S. port authority, national transportation agencies, and a trucking industry representative from both Canada and the United States. It was originally started in 1983 and called Crescent, but by 1985 the overall program was changed to HELP. The demonstration project itself is called Crescent, and it was started in 1991 and completed by 1993.

There were four goals for the HELP program. They were as follows:

  • Assess the viability of the technologies in the highway environment (e.g., reliability, accuracy, etc.).
  • Improve institutional arrangements (e.g., one–stop shopping, pre–clear at weight stations and ports of entry, border transparency).
  • Measure efficiency and productivity (e.g., improved safety, enforcement, reduced administration, data collection, etc.).
  • Identify additional applications of the technology (e.g., public/private sector applications) (Walton, 1991).

No specific results were found for Crescent as of the initial writing of this report. As with TravTek and other projects, results should be available during the duration of this project.

Additional CVO research findings

There are very few empirical and review studies that involved advanced technology and commercial vehicles in addition to the studies mentioned above. The few findings that were available are summarized below.

ITS America called attention to the differences between automotive and CVO populations. The IVHS America Strategic Plan (IVHS America, 1992b) stated that the average commercial driver differs from the average automobile driver in terms of such demographic characteristics as size, age, sex, and health, as well as such performance characteristics as information processing and response abilities in a multi–channel information system. The report stated that it is critical to examine driver characteristics specifically in the context of CVO (IVHS America, 1992a). In addition, the report stated that human factors considerations are important in developing CVO technologies. Areas that need to be studied include:

  • Information requirements issues.
  • Display issues.
  • Driver performance issues.
  • Driver behavior issues (IVHS America, 1992a).

Boehm–Davis and Mast (1992) specified that CVO systems designers must also consider identifying the information needed by the driver, the vehicle, and the control agencies (e.g., ATM's, fleet managers). Once the information has been identified, researchers need to identify the best means of presenting that information to users (Boehm–Davis and Mast, 1992).

HUD concepts for commercial trucks

HUD's allow the operator to access vital information without having to look down at the instrument panel. HUD's are currently used in many applications, including aircraft, automobiles, and trucks, and they have many potential advantages.

HUD's in trucks, however, require modifications due to windshield designs. Truck windshields are nearly vertical. Therefore, Greenland and Groves (1991) recommended using a separate combiner element as part of the HUD package and not using the windshield. This would avoid potential ray interference and low brightness. A separate combiner element would also allow the HUD to be a completely self–contained unit. So the HUD may be placed in any convenient location in the vehicle.

The application of ITS technology to hazardous material transportation

The regulations for transporting hazardous material lie in three areas:

  • Adequate packaging.
  • Communication of hazard information.
  • Operational requirements pertaining to the particular mode of transportation.

ITS will have the greatest potential for improving communications.

Allen (1991) suggested using "smart cards" that convey information for emergency response. These are similar to the existing diamond placards with numbers and symbols. He also suggested real–time tracking (AVL, TWC, and OBC), electronic manifest (AVI, AVC, TWC, and OBC), and smart package (TWC and OBC). "Smart package" would monitor the physical condition of high–hazard, volatile hazardous material cargo and packaging.

AVI research for commercial vehicle operations

Tests were conducted by Davies, Hill, and Siviter (1991) on current AVI systems that performed well with regard to height, offset, temperature, attenuation, speed, multi–lane, multi–tag, placement, accuracy, reliability, and interference. The results found that although none of the commercially available systems performed without significant operational problems, those based on radio–frequency technology showed the most promise. A prototype was then built using the results obtained in the first study. Davies, Hill, and Siviter (1991) outlined principal features of the final specifications for the AVI beacon system.

Ferlis and Aaron (1977) described an AVI system that incorporates a transponder that carries a unique vehicle identification number and an interrogator that extracts the vehicle identification number from the vehicle; a communication system that transmits the vehicle information to a central computer for processing; and a computer that manages, stores, edits, and analyzes incoming data. The technologies that could be used for AVI systems are broad. Radio–frequency (RF), microwave, radioactive, magnetic, license–plate scanning, and visible–optical scanning are all potentially viable. Koelle (1991) indicated that the technology employed in the Ametech AVI system is powered by either RF or built–in battery.

AVI technology, as outlined in the literature, has several potential applications (Ferlis and Aaron, 1977; Koelle, 1991; Larson, Colton, and Larson, 1977). Koelle (1991) described how Ametech Systems Corporation has used AVI systems technology in electronic toll collection. Various toll roadway systems have used Ametech's AVI systems, which have proven to be both reliable and cost–effective. Koelle noted that in mid–1991, there were in excess of 120,000 in use. According to Koelle, public acceptance of this technology was highly favorable.

Ferlis and Aaron (1977) described other potential AVI applications. In addition to toll collection, access control can be managed. Based on the vehicle's identification number, vehicles' access to outlined locations can be determined. For example, "cordon control" (which prohibits certain motorists from traveling during certain times or locations) can be facilitated by AVI systems. Another potential application is data collection. As vehicles are identified at particular points, traffic measures, including volumes, vehicle classification, travel times, and travel paths can be collected. Traffic signal control is another application of AVI technology. By identifying traffic flow, control of the offset relationship of a series of signalized intersections could potentially decrease congestion.

Automatic vehicle monitoring

An extension of AVI technology is Automatic Vehicle Monitoring (AVM). In addition to providing vehicle identification information, AVM provides both status and location information. Fleet management has been identified as a potential application of AVM technology. Ferlis and Aaron (1977) outlined three benefits that AVM technology could have on fleet management. These included reducing or eliminating manual data collection through automatic passenger counts, reducing scheduled layover time because of improved schedule adherence, and freeing buses by enabling schedules to lengthen headways without increasing passenger's perceived waiting time. AVM has also been used by police department dispatchers. Larson, Colton, and Larson (1977) described a system that has been tested by the St. Louis Police Department. Results of the testing suggested that there is potential for implementing an AVM system that may decrease response time, increase officer safety, and decrease the voice–band congestion that presently exists.

Follow–up studies on the success of AVI and AVM technology are absent from the literature. Ferlis and Aaron (1977) examined the feasibility of this technology. Results of a feasibility study indicated that due to the high cost of technology, it may not be feasible. Note that this examination is dated. Further examinations of AVI technology, including its feasibility, effectiveness, safety implications, and attitudinal factors, are required.






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