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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





ATIS/CVO research to date has been system description–oriented, with details of organization of research that is in process or needs to be conducted. There are many human factors research issues that need to be addressed before a comprehensive set of guidelines can be developed. However, as shown in this report, a number of issues have been resolved for ATIS systems and comparable systems and need not be re–addressed. It is apparent that as the development of hardware progresses, the next few years will see a marked growth in the literature available from both U.S. demonstration projects and foreign sources. Therefore, as the research planning phase of this project progresses, it is critical to continue reviewing current studies. Currently, the largest gap in findings is within Japanese research. Apparently, there is such a drive to get products to market in Japan that little human factors–type testing is done before products are released. This is not to say that the products are poorly designed, but the danger does exist of producing a product with a high workload demand. It is also possible that the information does exist, but that the publication of research findings stays within Japanese journals or never leaves the company whose system is being tested. Unlike the European system of development, the Japanese system is very competitive, and studies that could leak product information are withheld to maintain corporate secrecy.

In general, specific ATIS research is lacking for IVSAWS and ISIS applications. Although these ATIS systems generally do not have complex user interfaces, they present unique human factors and safety issues. IVSAWS is an alarm type of display; therefore, issues of timing, modality false alarms, and potential operator reactions must be addressed. Many ISIS issues are similar to IRANS and IMSIS; however, presentation of regulatory information carries with it critical issues of message reliability, priority, understanding, and interpretation.

In many ways, CVO research is leading the way for automotive ATIS applications. However, the types of CVO applications that are feasible and desirable are significantly broader in scope than automotive applications. Greater functionality can be provided for the driver because of demographics and greater opportunities for driving. However, issues of overload and driving intrusion are just as critical, if not more so.

Documents for human factors and safety research

There are two noteworthy reports guiding human factors and safety research. The first is the ITS report by Barb and Mast (1992), Safety and Human Factors Considerations, which is the product of a conference held at UMTRI in December 1990. The four working groups for ITS–Automatic Traffic Management Systems (ATMS), ATIS, Automatic Vehicle Control Systems (AVCS), and CVO–convened and formulated research recommendations.

The second major report is by Sheridan (1991) and is titled Human Factors of Driver–Vehicle Interaction in the IVHS Environment. This report does not contain focused information on CVO. However, ITS effects are dealt with in terms of human factors theory and models, such as human error, mental workload, cognitive models, control theory and dynamics, information processing, dynamic decision theory, and signal detection theory. The report also discusses experimental program needs for understanding and evaluating ITS safety.

Besides these two reports, the Transportation Research Board (TRB) has also produced relevant publications. A comprehensive inventory of 19 safety issues are categorized into 5 areas in the 1991 TRB circular #375, Strategic Highway Plan. Their framework consists of people, vehicles, highway environment, post–crash, and safety management. In TRB record #1318, Safety and Human Performance, Highway Systems, Human Performance, and Safety 1991, articles by Hitchcock (1991); Hungerford, Sperling, and Turrentine (1991); Khattak, Schofer, and Koppelman (1991); Taoka (1991); and Turrentine, Sperling, and Hungerford (1991) are presented. The four relevant article topics are:

  • Driver warning and co–pilot devices.
  • Problems of requirement specification and hazard analysis.
  • Engineering design concept for ITS safety.
  • Real–time responses to in–vehicle ITS in Europe.

Each of these sources should be used to develop research requirements. In addition to these findings, a number of research requirements were addressed in the other literature reviewed as part of this report. Also, the authors have identified gaps that were apparent from a lack of research activity. The above–mentioned research requirements are combined and described in the next section.

Specific research requirements

Research on in–vehicle guidance display systems is still needed to determine the effectiveness of different message lengths and wording, and icon effectiveness and salience. More research is also needed to determine the most effective voice–based guidance system. Several factors to be investigated include synthesized versus natural speech, voice in combination with text, and the style in which information is presented.

Advisory system display characteristics require further investigation. Optimal character size and screen density need to be determined for older and younger drivers. Standard icons that most effectively present information to drivers of all age groups need to be developed. Further research on vertical disparity should be performed to determine its effect on reaction time.

Zwahlen et al., (1987) suggested that the use of touch–panel controls in automobiles should be reconsidered and delayed. More research dealing with driver information acquisition, information processing, eye–hand–finger coordination and touch accuracy, control actions, and safety aspects needs to be conducted, and the designs and applications need to be improved to allow safe operation during driving.

Research is needed to determine the effectiveness of advisory systems in identifying drunk drivers and deterring them from driving. Effective warning systems are needed to advise alcohol–impaired drivers of potential hazards. Engineering adaptations, such as the use of protected left–turn signals, need to be investigated to help determine if they will prevent accidents caused by alcohol–impaired drivers.

In general, further research is needed to investigate the information needs of drivers. The needs of urban, rural, local, and visiting drivers must be determined. The amount of information available to drivers upon request and the amount provided to drivers normally must be determined. Research is also needed to determine how much information should be provided to drivers in the case of incidents and alternate route selections.

Barrow (1990) made three research recommendations:

  • Driver perceptions and attention selection techniques need to be understood.
  • Effects of monitors, as opposed to HUD's, need to be determined.
  • Standards across manufacturers are needed to hold down the complexity of interfaces and establish user–friendly systems. NHTSA should define basic guidelines.

Barb and Mast (1992) made the following recommendations for research on six areas of "Plain Old Driving" (POD):

  • Environmental complexity and information needs for basic driving.
  • Driver's mental models.
  • Mental workload.
  • Dynamic eye and body movements.
  • Driver cognitive and sensory motor response to highway incidents.
  • A taxonomy of driver errors.

In order to define driver needs, research and development are needed as described below (Barb and Mast, 1992):

  • Detailed specification of the information is needed by the driver to make each ITS function effective.

  • Which sensory display modes and associated information format and density are most appropriate for each of the ITS functions. Visual display information should be coded to allow for aggregation from successive glances. Timing of information presentation includes speed, control activation, traffic density, headway, weather, and driver characteristics such as age and ability.

  • Determination of which associated data entry and function selection encoding and formats would best support the above items (hard keys, soft keys, voice recognition, or cursor control).

  • Task analysis and error taxonomy for ITS interactions.

  • Development of design–oriented human factors guidelines for displays and controls for the multiple ITS functions and for their integration.

The following items are needed to improve tools for data collection (Barb and Mast, 1992):

  • Rapid prototyping through computer graphics and modular systems for use in actual vehicles.
  • Modification to test tracks or actual highway networks to allow ITS experiments.
  • Simulators measuring drivers' responses to incidents.
  • Techniques for setting up and using focus groups in experimental measurements and demonstration projects; use of clinic technology to determine user acceptance.

Various data bases need significant improvements (Barb and Mast, 1992):

  • An improved means to compile data statistics on traffic congestion build–ups, lane blockages, and resultant vehicle responses.

  • Improving accessibility and usability of ITS–related human factors data code for use by researchers, designers, and government agencies.

  • Defining procedures for future accident reporting and debriefing on ITS–equipped vehicles. On–board recorders, like those in aircraft, may be needed to augment self–reports and police reports.

  • Research to provide indicators and models that lie between detailed measures of human and vehicle behavior, and ultimate safety criteria (mortality). Researchers must determine when additional information causes overload or "pollution."

  • Finally, a new generation of ITS–sensitive engineers and human factors people needs to be trained.

Sheridan (1991) proposed the following specific ATIS–related experiments:

  • Simulator experiments in map interpretation and navigation while driving. Driver's ability to read and understand navigation information from maps, symbols, and text, in various combinations, is of particular interest.

  • Simulator experiments in dynamic warning. Scenarios of interest include imminent collision, which requires the fastest response; intersection hazard; turn required by prespecified routing; and surrounding traffic situation. Immediate steering or braking is required in all of these scenarios.

  • Measurement of vehicle/driver safety status. Trouble can be detected in incipient stages, and sensors need to be developed to do so by analyzing vibration signatures and other combined factors. Researchers also must ask if risk homeostasis will occur as people perceive they are safe and increase their level of risky driving. Definitions of "safe physiological and psychological" status need to be defined, along with methods to measure them.

  • Technology forecast/assessment of communication off highway and with other vehicles. Researchers must ask if people will try to create a mobile electronic office with telephone, fax, computer, printer, pager, and answering machine, and what are the negative consequences of using such devices. Also, will commuting become a more social activity, and how will that change the commuter culture.

Gould (1989) makes the following observations.

As researchers await technological breakthroughs, there is a need to focus on the mode by which people structure or allocate space and on how they later recall and use that information. This will be key to designing optimal vehicle navigation systems. Individual cognitive differences also need to be considered. Stasz and Thorndyke (1980) found that the best predictor of their definition of map learning was the Building Memory Test from the Educational Testing Service. The test uses building position recall from a street map. Sholl and Egeth (1980) found that map reading and map learning have separate cognitive bases and that general mathematical and verbal abilities were strong predictors of map reading ability.

Sadalla and Hauser (1991) make the following research recommendations:

  • Driver situations need to be classified in terms of their stress–producing potential. Currently, there is no means of calibrating the relative stress –producing potential of either roadway design variables and/or traffic congestion variables. Also, more needs to be known about the extent or duration of traffic–induced stress.

  • Exploration of the relationship between aging and driving stress is necessary. A hypothesis is that "as people age, they should become more physiologically and psychologically stressed by traffic." Variables of roadway design and traffic situations that contribute to elderly drivers' stress need to be quantified.

  • Investigate the long–term cumulative impact of driving stress on both younger and older drivers. Longitudinal studies have not been performed, but are necessary to measure changes in health. Both prospective and retrospective research designs should be used.

  • Mechanisms that mediate the relationship between driving stress and health changes should be explored. Effects of driving stress on the immune and cardiovascular systems need to be clarified.

  • A psychometric instrument needs to be developed to specifically measure resistance to driving stress. Questions should include the following topics: hardiness, locus of control, sensation seeking, Type A behavior, risk taking, and dominance, as they relate to driving.

  • A validation of the driving stress instrument as it pertains to subjective distress and physiological reactivity is needed.

  • Validation of the instrument as a moderator between driving stress and health is needed, as well as a longitudinal study of drivers exposed to high levels of traffic stress. According to the instrument, higher scores should indicate more health problems.

  • An evaluation of the relationship between traffic stress, personality, and immune system response is needed. Neuroimmunological research identifies the associations between specific subjective psychological states, neuroendocrine processes, and the immune system. Noninvasive tests of saliva can be done using a technique of radio immunoassay. Experiments that examine variable interactions include stimulus variables, individual differences in stress susceptibility, and immune system response.

Marans (1990) made the following recommendations regarding user acceptance, in which three research areas were identified. The University of Michigan is planning the following:

  • In–depth interviews with automobile and electronic industry decision–makers, as well as government planners.

  • A nationwide, ongoing household survey of the driving public. The sample will be segmented across geographic region, size of community, and selected socio–economic characteristics.

  • Conduct a literature review of previous research on driver acceptance of new technologies at the level of individuals, organizations, and societies.

Boyce (1988) posed the following research questions:

  • What are the likely savings in travel time from user–optimal route choices as compared with existing dispersed route choices?

  • What additional savings would result from the introduction of system–optimal route choices and the timing of traffic–signal systems with better historical and real–time information?

  • How would improved highway travel time information change the behavior of commuters with regard to departure time, choice of mode, and choice of residential or job location? What would be the benefits or costs of these changes?

Burgett (1991) described some of the safety hypotheses associated with the TravTek system:

  • Hypothesis: If it takes no more time to gather information from a display of TravTek information than it does to gather information about some other functions, such as climate control, then the TravTek display is as safe as the climate control display.

  • Hypothesis: TravTek will relieve the burden of "loading tasks," such as seeking exits from a congested freeway, which will prevent attention overload.

  • Hypothesis: For fixed roadway characteristics (e.g., speed limit and number of lanes), collision rates will vary directly with the level of congestion.

  • Hypothesis: Collision severity will vary inversely with the level of congestion.

  • Observation: Data will be indirect measures of safety–precursor events to collisions since ITS TravTek collision data do not exist. Precursor events are lane deviation and reduced headway.

Fleishman (1991) listed the research and evaluation questions for the TravTek ITS Operational Field Test:
  • Does TravTek allow a statistically significant reduction in speed variance?
  • Does TravTek allow a statistically significant reduction in number of stops or instances of zero speed per trip?
  • What is average speed per trip?
  • What is average number of miles per trip?
  • What is the number of new routes offered to drivers because of congestion/traffic incident information?
  • What is the number of new routes accepted?
  • What is the frequency of broadcast/reception of Dynamic Link Ratios?
  • What are the types of incidents, start and end times, and locations of incidents?
  • How often are trips avoided?

CVO–specific research requirements

Given that the average commercial driver is likely to be quite different than the average automobile driver in terms of demographic characteristics such as size, age, sex, and health, and performance characteristics such as information processing and response abilities in a multi–channel information system, it is critical to examine driver characteristics in the context of CVO (IVHS America, 1992a).

It is important to considers human factors when developing CVO technologies. Areas that need to be studied are:

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

Researchers must identify the information needed by the driver, vehicle, and control agencies (e.g., ATMS, fleet managers) and then identify the best means of presenting that information to users (Boehm–Davis and Mast, 1992).

Barb and Mast (1992) described several CVO research needs and questions that need to be addressed:

  • Characterization of truck drivers, trucks, and truck operations in a representative manner so that Human Factors and Safety (HF and S) studies can adequately address the application of ITS to trucking.

    Drivers. What is the distribution of human performance–related properties over the truck driver populations and what is their state while driving?

    Vehicles. What are the truck control characteristics and other physical attributes that impact upon human factors and safety issues?

    Road network. What is the time/space characterization of truck routing?

    Motion environment. What is the time/space characterization of vehicle movement in the immediate proximity of heavy trucks, such that collision prevention technologies can be quantitatively specified?

    Information. What truck–specific information flow characterizes current operations?

    Operations. What characteristics of commercial truck transport operations influence the driver's daily workload and the safety risks?

    Regulation. What regulatory and enforcement practices influence operational safety going down the road once the driver and vehicle have been duly licensed?

    Accident studies (study of heavy vehicle accidents and their causes in light of potential ITS interactions). Issues of interest include commercial vehicle maneuvers at the time of a destabilizing event, critical driver errors, characterization of non–police–reported accidents, and congestion caused by specific types of truck accidents.

  • Definition of safety needs and determination of performance targets to be achieved through the application of ITS technology to trucking. Primary areas include the following:

    System safety. What targets or potentially achievable benefits can be set for the overall safety of improvements in trucking operations derived from ITS application to CVO, considering driver, vehicle, and system–level factors?

    Truck control. What specific opportunities exist for truck control and warning aids employing ITS technology? What performance requirements can be stipulated as a means of defining such opportunities?

    Cockpit design. What features in the design of ITS displays within the truck cab can be stipulated or constrained as requirements?

    Driver training. What opportunity is there to use ITS technologies as a training tool for truck drivers or dispatchers? What special training may be needed to attain ITS literacy or ITS operability among truck drivers?

    Hazards. What are the specific requirements for materials for the ITS functions serving to improve the safety of hazardous materials transportation?

    Auto inspections. What performance requirements or targets can be stipulated for ITS applications that operate in real–time to confirm the physiological, licensing, and hours of service compliance of truck drivers and the mechanical state of trucks as they pertain to safety?

    Truck routing. What are the requirements for routing constraints that must be incorporated within route guidance and navigation functions to reflect access limitations applying to large trucks?

  • Development of methodologies (including research protocols and tools) for studying the HF and S issue involved:

    Rapid prototyping. Develop tools for rapidly prototyping ITS packages to be used in truck development and research on user cabs, so as to expedite the engineering friendliness.

    Crash avoidance. Develop the protocol for evaluation of crash warning and crash intervention systems intended for CVO application.

    CVO driving. Develop one or more levels of driving simulator capable of representing the CVO driving environment.

    Crash recorders. Low–cost, rugged devices for research on causal elements in truck accidents with specific attention to pre–crash data indicating accident modalities and opportunities for automatic countermeasure.

    Safety benefits. Develop the means to assess the accident reduction benefits of ITS as they accrue to CVO, recognizing that traditional data sources and analyses have focused upon the results of impact rather than the causal factors.

  • Conduct applied research and operational testing to determine the human factors acceptability and safety–effectiveness of ITS technologies applied to trucking:

    User acceptance. Study in a market prediction sense the predisposition of truck drivers, dispatchers, managers, and regulatory enforcement people to specific systems and categories of systems.

    Display. Study the constraints upon display technologies within the authentic truck cab environment characterized earlier by certain vibration, noise, lighting, and geometric layout parameters.

    Workload tolerance. Study driver tolerance for workload changes requiring the need to interact with in–cab information functions for advanced systems.

    Route guidance. Identify the problems posed when presenting route guidance to the truck driver.

    Dynamic warning. Study the application of dynamic warning systems to heavy–duty trucks and truck combinations. This includes inter–vehicular collision, run–off–road, and rollover warnings.

    Driver monitoring. Study the application of driver monitoring systems to CVO drivers, with examination of both the sensory technology and the systems considerations of data interpretation and usage in an alerting approach.

Summary of Knowledge Gaps Key to the Development of Human Factors ATIS/CVO Guidelines

ATIS/CVO research to date has been system description–oriented, with details of the organization of research that is being conducted or needs to be conducted. There are many human factors research issues that still need to be addressed before a comprehensive set of guidelines can be developed. However, as shown in this report, a number of issues have been resolved for ATIS or comparable systems and need not be re–addressed. As the development of hardware progresses, the next few years will see a marked growth in the literature available from both U.S. demonstration projects and foreign sources. Therefore, as the research planning phase of this project progresses, it will be critical to continue reviewing current studies.

The ITS literature produced to date aids in the development of the initial phase of ITS. However, because there is a lack of empirical data, the development of comprehensive guidelines is that much more dependent on analysis, modeling, and empirical research.

It is anticipated that the data from initial U.S. operational tests and additional European and Japanese projects will fill some of the gaps in the human factors knowledge base. TravTek, as previously described, has a number of IRANS and IMSIS features and will provide data from numerous studies with well over 1.6 million km (1 million mi) of data collected. The University of Michigan Transportation Research Institute's (UMTRI's) project also will provide data, as well as preliminary models that may help in the establishment of guidelines. The ADVANCE and Guidestar projects promise data from even larger groups of users in the near future.

In order to develop comprehensive and general guidelines that are useful for years to come, models of driver performance while using ATIS and CVO systems must be developed. This research will likely include application and/or modification of existing models (e.g., UMTRI or model driver processing proposed by Sheridan, 1991, or Kantowitz, 1990), as well as creation of new models or model parameters associated with ATIS/CVO–specific applications.

In general, ATIS research is lacking IVSAWS and ISIS applications. Although these ATIS systems probably will not have complex user interfaces, they present unique human factors and safety issues. IVSAWS will be an alarm display; therefore, issues of timing, modality false alarms, and potential operator reactions must be addressed. Many ISIS issues are similar to IRANS and IMSIS; however, presentation of regulatory information carries with it critical issues of message reliability, priority, understanding, and interpretation.

In many ways, CVO research is leading the way for automotive ATIS applications. However, the types of CVO applications that are feasible and desirable are significantly broader in scope than automotive applications. Due to differences in driver demographics and greater opportunities for training, greater functionality can be provided for the CVO driver. However, issues of overload and driving intrusion are just as critical, if not more so, for CVO applications when compared to automotive applications. In addition, system design alternatives that would be unacceptable for automobile drivers due to cost and/or acceptability/marketing constraints may be acceptable for certain CVO applications. Therefore, a number of CVO–specific empirical projects must be undertaken to establish guidelines for the broad scope of useful CVO functions.

In general, further research needs to be performed to investigate the information needs of both automobile and CVO drivers. The information needed only by urban, rural, local, and visiting drivers must be determined. The amount of information available to the driver upon request and the amount provided to the driver normally must be determined. Researchers also need to determine how much information should be provided to the driver in the case of incidents and alternate route selections.

Driving capacity is a major research gap requiring both the application of existing guidelines and the creation of new guidelines. The human factors community is currently divided on the issue of what is safe and what is unsafe in the driving environment. The primary cause of this debate has centered around IRANS applications and will require additional research to resolve. In addition, many of the more difficult issues relating to resource capacity for trained CVO drivers and multi–function systems have not been addressed empirically or descriptively. Carefully planned and executed experiments that provide general principles instead of system–specific do's and don'ts are needed. In addition, an understanding of potential safety benefits and the costs of using ATIS/CVO are needed for guideline development. It is easy to dismiss a display that provides complex information as requiring too many driver resources. However, until (1) a comparison is made with current techniques for retrieving necessary information, and (2) an assessment is performed to determine the benefit of having the information, a proper assessment cannot be made.

Driver acceptance of ATIS and CVO technology also needs to be researched. Even a safe and efficient system design will not achieve the goals of ATIS and CVO systems if the needs and desires of the user are not met. Poor market penetration will result. Although a number of surveys have been conducted and describe desirable ATIS and CVO features, ongoing research is necessary to establish the information and control requirements for system (and product) success. Once information requirements have been established, human factors design guidelines can be established.





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