Applying the Operational Design Domain Concept to Vehicles Equipped with Advanced Driver Assistance Systems for Enhanced Safety

. Advanced driver assistance systems (ADASs) assist drivers by alerting them of the occurrence of events based on the sensing capabilities of the vehicle, reducing the efort required by drivers. Most vehicles that are recently launched vehicles have been endowed with ADAS, thereby signifcantly reducing trafc accidents. However, the Insurance Institute for Highway Safety has reported that trafc accidents caused by driver negligence may increase as drivers have become accustomed to using ADAS. Terefore, drivers must be provided with sufcient information on the appropriate use of ADAS through user manuals. In this study, the regulations regarding the presentation of the operational design domain (ODD) in ADAS user manuals were analyzed. Te results indicated that most user manuals do not sufciently specify the ODD, which is claimed important by various organizations for ensuring safe driving. Additionally, the expression of the limitations and performance of ADAS is ambiguous because most countries are not regulated to explicitly present the ODD when writing ADAS user manuals. Terefore, in this study, the ODD guidelines for presenting ADAS specifc to vehicle manufacturers and governments have been outlined in addition to guidelines for drivers on using ADAS. Tese guidelines can contribute to the development of clear ADAS user manuals, which in turn can ensure the safe driving of ADAS-equipped vehicles.


Introduction
Advanced driver assistance system (ADAS) technology assists drivers with respect to lane keeping, vehicle speed management, and automated braking systems [1].Tese systems are primarily designed to improve driver comfort and ensure safe driving through warnings and active intervention in situations that warrant the implementation of necessary actions [2].Te rapid development of ADAS has led to both luxury vehicles and low-end vehicles being equipped with ADAS functions, such as autonomous emergency braking (AEB) [3].
According to the Insurance Institute for Highway Safety, the trafc accident rate has decreased by 41% after the application of forward collision warning (FCW), a major safety function of the ADAS, to trucks [4].However, trafc accidents may continue to occur owing to the negligence of drivers who are accustomed to using ADAS [4].Terefore, Teoh [4] proposed a system that requires the active participation of drivers when using ADAS technology.
In 2020, the Korea Consumer Agency conducted a survey of 500 consumers driving vehicles that were launched after 2018.Te survey results indicated that only 8.2% of the consumers were aware of the ADAS-related content in the user manuals and only 9.9% had read the manuals.Furthermore, more than 50% of the consumers indicated difculty in obtaining useful information from the manuals because of their unsatisfactory portability and readability.Terefore, trafc accidents caused by the use of ADAS can be attributed to driver negligence.Moreover, the nonstandardization of ADAS manuals has been considered disadvantageous [1].
Automated vehicles (AVs) exhibit tremendous potential to increase road capacity, promote transport safety, and reduce fuel consumption [5].Based on the rapid development of automated driving systems (ADSs), the Society of Automotive Engineers (SAE) International has defned ADS levels 0-5 in six stages [6].For automated driving level 3 or higher, methods for systematically managing user manuals are globally under discussion.Furthermore, by clearly presenting the operational design domain (ODD) of AVs in user manuals, safe driving can be ensured by increasing the driver's understanding of AVs.However, quantitative and qualitative analyses of user manuals sold in Australia in 2018 indicated that ADAS functions corresponding to automated driving levels 1 and 2 of SAE were not systematically managed because drivers were not well informed about their use [1].Tis implies that the generalized ADAS technology does not provide sufcient guidance to drivers to ensure safe driving compared with high-level ADSs.
Terefore, this study explores a user-friendly method of applying the concept of ODDs used in AVs to ADASequipped vehicles to provide better guidance to drivers.User manuals of vehicles sold in Korea between 2016 and 2021 were acquired.Te target vehicles in this study were equipped with ADAS corresponding to levels 1 and 2 defned by SAE.Te manuals of ADAS-equipped vehicles were reviewed, and the presentation of content related to the ODD was scrutinized.Based on the analysis, guidelines for presenting ADAS functions in user manuals for drivers are individually suggested to manufacturers and governments for improving the driving safety of ADASequipped vehicles.

Current Status
2.1.1.Defnition of ADAS.Te ADAS technology assists drivers in driving tasks, thereby increasing driving safety and efciency.Although ADAS can enhance driver comfort, the primary purpose of this technology is to ensure safety [7].ADASs correspond to automated driving technology classifcation levels 1 and 2 of SAE with the driver as the driving subject.Although ADAS functions are similar for all vehicle manufacturers, their names and performances difer.
Te most common method for recognizing the functions and limitations of ADAS technology in vehicles is to read the manual provided by the vehicle manufacturer [8].Most manuals present the limitations of ADAS technology in the form of "restrictions" or "cautions."Te manuals also state that ADAS technology may not operate accurately under certain circumstances depending on weather, lighting, roads, lane markings, and other features.

Types of Commercialized ADAS Functions.
In this study, commercialized ADASs were classifed based on their functions into systems that ensure driving safety, driving convenience, parking safety, and parking convenience.Table 1 lists certain examples of ADAS functions and their classifcations.

Concept of ODD.
ODD defnes a specifc operating environment to identify the conditions under which ADSs can operate normally and safely.Te ODD includes the operational limits of the subject ADS, safe driving conditions, and driving conditions, such as road type, specifc time, weather, and communication environment.Te J3016 document of SAE defnes ODD as follows [6]: "Operating conditions under which a given driving automation system, or feature thereof, is specifcally designed to function, including, but not limited to, environmental, geographical, and time-of-day restrictions, and/or the requisite presence or absence of certain trafc or roadway characteristics." In other words, the ODD is an environment where an ADS can be stably used.To standardize the ODD, the Automated Vehicle Safety Consortium (AVSC) of SAE, Public Available Specifcation (PAS) 1883 of the British Standard Institution (BSI), and National Highway Trafc Safety Administration (NHTSA) defned the ODD and classifed its elements [9].
Te AVSC of SAE developed an ODD framework for the operation and maintenance of AVs.Te ODD framework was developed to establish standardized details and a scope that could be understood by ADS developers, testers, and distributors.Te AVSC defnes ODD using both top-down and bottom-up methods [6].
Te BSI frst published a taxonomy of ODDs and aimed to provide common terms for describing operating conditions, such as driving situations and environments, to enable automated driving.Te BSI classifes ODD in a hierarchical form using scenery, environmental conditions, and dynamic elements as the major categories [10].
NHTSA presents a framework for evaluating specifc features of automated driving technology.Particularly, the ODD was classifed into six elements, namely, physical structure, operation limit, object, communication, environmental conditions, and zone, such that the operable ODD range could be identifed for ADS levels 3-5 [11].NHTSA provides guidelines for AV development through "automated driving systems: a vision for safety 2.0."Tis guideline specifes that AV developers should conduct simulations and on-road tests that consider ODD for safety verifcation [12].

Previous Studies
2.2.1.ODD Analysis.Gyllenhammar et al. [13] reported a framework for safe operational conditions of ADSs.Initially, they generated use cases by considering the environment in which the ADSs would be used.Subsequently, an ODD that included the environments depicted in the use cases was specifed; however, the ODD was modifed when 2 Journal of Advanced Transportation Czarnecki [14] revised the method for setting the ODD classifcation criteria using SAE.As SAE emphasizes the necessity for monitoring ODDs, a restricted operational domain (ROD) was defned as a superordinate concept of ODD.Czarnecki [14] suggested that the use of an ADS should be limited by establishing an ROD when a defect occurs in an AV when driving, which afects the object event detection and response of the AV.Furthermore, a degraded operation mode involving a faulty vehicle was defned and the ROD monitoring was presented to determine the application status of ROD as a system architecture [14].

Vehicle Manual Analysis.
Oviedo-Trespalacios et al. [1] analyzed user manuals provided to drivers to ensure the safe use of ADAS.Tey analyzed the diferences in the content and readability of ADAS-related information in the manuals of vehicles with high sales in Australia.Seven themes were identifed in the manual, including notifcation of diferences, familiarization, operational limits, potential ADAS errors, behavior adaptation warnings, confusion warnings, and malfunction warnings.Te analysis results indicate that most manuals warrant a lengthy duration of the study to be understood by the general audience and that they contain numerous confusing texts and infographics.Moreover, regulators and stakeholders from the industry should participate in reducing the discrepancy caused by the lack of standardization in terms of both content and information delivery.
Capallera et al. [15] analyzed the factors afecting ADAS and the limitations of manuals by examining diferent models from 12 luxury vehicle manufacturers.Herein, the factors afecting ADAS were similar to those of ODD suggested by SAE.Te factors comprised six major categories, namely, natural environment, human factors, roads, lanes, obstacles, and vehicle conditions, and 26 subcategories.Te results indicate that except for certain common elements, most manuals do not communicate the information clearly.Furthermore, they determined that the limitations of ADAS should be presented more comprehensibly.Additionally, human-machine interaction (HMI) should be used to communicate the unsafe implementation of ADAS.
Ito [9] reported that no standard method exists for describing the ODD of AVs and only a few elements (e.g., the external environment and existing ODDs) should be connected to the ADS.Additionally, as the content must be understood by each user, documents describing sODD should provide appropriate information in terms of safety and maintain consistency with standards and guidelines.

Summary. Several defnitions of ODD and various analytical methods have been proposed in previous studies.
Te defnition and presentation of ODDs can be examined by analyzing vehicles' user manuals.A review of previous studies revealed that despite diverse classifcation criteria for ODDs, the ODD of ADAS is not clearly presented in user manuals.Moreover, the functions and limitations of ADAS are not easily recognized from the driver's perspective when using the manual.
Terefore, the subsequent sections of this paper defne the essential and additional elements of ODD by analyzing various ODD defnitions and user manuals.Additionally, the presentation of ODDs for ADAS is analyzed by examining the user manuals of vehicles sold in Korea.Based on the analysis, this study proposes guidelines for governments and manufacturers to deliver clear information to consumers regarding ADAS functions.Furthermore, guidelines have been provided to drivers for the efcient use of ADAS technology.

Analysis of ODD Classifcation and Presentation.
Tis section presents two analyses.First, an ODD classifcation analysis was performed to identify the essential and additional elements of ODD by comparing the classifcation criteria and content associated with ODDs of the SAE, BSI, and NHTSA, which are representative organizations that defne the ODD elements and limitations of ADSs.Te ODD elements that must be explained in the user manual were defned by deriving the essential and additional elements.Second, an ODD presentation analysis was performed to examine the relative importance of ODD elements and presentation methods.Te frequency of ODD elements expressed in user manuals was calculated, and the importance of the ODD elements provided by vehicle manufacturers to drivers was examined.Finally, the methods for presenting the driver with the limitations and operating conditions of ADAS in the manuals were investigated.

Characteristics of ODD.
Various international organizations have attempted to standardize ODD.In this study, the ODD classifcations of SAE, BSI, and NHTSA were compared.
According to the SAE J3016 document, ODD restrictions must be applied to automated driving levels 1-4, and in areas outside the ODD, drivers must perform dynamic driving tasks.However, the ODD is not clearly defned for automated driving levels 0-2.
Te BSI defnes the requirements for minimum hierarchical classifcation in its PAS-1883 document to establish an ODD for the safe use of ADSs.Herein, the ODD aims to provide a general classifcation system for all environments in which automated driving technologies are tested or used.Te document presents the hierarchical classifcation requirements for ODDs based on automated driving levels 3 and 4 that are also applicable to ADAS.Additionally, the document states that ODD elements should be established based on a mutual agreement between manufacturers and stakeholders and compliance with ODD must be verifed via monitoring.Te document provides examples for specifying an ODD for each ADS, and they are presented in the ODD defnition checklist and text formats [6].
Te BSI ODD classifcation was established in a topdown manner, with seniority, environmental conditions, and dynamic elements considered as major categories.Te classifcation comprised 108 elements in 10 and 21 subcategories [10].
NHTSA presents a framework for evaluating specifc functions for the development of ADSs [11].Particularly, a taxonomy is presented for levels 3 and 4 in AVs to verify whether the ADSs operate within an ODD.Te NHTSA ODD classifcation system is defned in the hierarchical form of upper and lower categories, with each category comprising classes.Additionally, various ODDs provide an identifable and structured approach.Physical infrastructure, operational constraints, objects, environmental conditions, connectivity, and zones are identifed as the major categories.Tis classifcation comprises 138 elements in 20 subcategories.

Determination of Essential and Additional ODD
Elements.As explained earlier, ODDs are defned diferently depending on the organization.Te SAE defnes the necessity and degree of application of an ODD for each ADS level.Te BSI defnes an ODD for vehicle manufacturers and stakeholders, whereas NHTSA defnes an ODD for the assessment and development of ADSs.However, common classifcations and elements have been identifed in diverse ODD systems presented by various organizations.Terefore, in this study, the ODD elements commonly classifed by at least two organizations were considered essential elements, and the remainders were deemed additional elements.Te SAE's ODD framework has been identifed as somewhat general in its categorization, with a noted limitation in its failure to refect specifc subelements such as "vehicle entry and egress" [16].Additionally, because the BSI's ODD framework is defned in the format of a standard, it lacks clear hierarchical structuring among the major ODD categories, which may result in complexity for the general public to understand.Terefore, we have summarized the essential and additional elements based on the NHTSA's ODD framework, which is well structured in terms of categorization hierarchy and more accessible for the public to comprehend.
Te essential ODD elements include most of the elements that are typically defned by both NHTSA and SAE.Te primary categories of essential ODD elements are physical infrastructure, operational constraints, objects, environmental conditions, connectivity, and zones.Table 2 lists the classifcation comprising 110 essential elements in 22 subcategories.
Additional ODD elements are those included in the ODD system of only one organization; Table 3 lists the additional ODD elements.
As summarized in Table 3, the ODD elements of NHTSA, SAE, and BSI difered in most of the primary categories, except "zones."Te additional elements in the physical infrastructure indicate diferences in a few subcategories, including the roadway type, roadway surface, roadway edge, and roadway geometry; BSI defnes most of these elements.In fact, BSI provides a fner breakdown of the elements than other organizations.Tis is because the recognition ranges of the LiDAR and camera based on the pavement material of the road are important for classifcation in BSI.

Analysis of ODD Presentation
2.4.1.User Manual Acquisition.Te readability of user manuals of major vehicle manufacturers in several countries is unsatisfactory.Furthermore, the methods that express technical limitations difer among manufacturers.Terefore, manuals for the latest vehicles were acquired in this study, including those of 31 vehicle models from 15 manufacturers (Table 4).

Analysis of Exposure Frequencies of ODD Elements.
If a vehicle manufacturer explains any ADAS-related ODD element in the user manual, it is assumed that the manufacturer considers the element sufciently important to provide its information to drivers.Furthermore, if an ODD element is frequently mentioned in the manual, it is assumed that the manufacturer considers the element to be more important than others.Terefore, in this section, the exposure frequencies of the ADAS-related ODD elements expressed in each user manual are calculated.
ODD elements with high exposure frequencies were those that were mentioned in more than one-half (16 or more manuals) of the 31 user manuals, and the exposure frequencies of these elements are summarized in Table 5.Table 6 lists ODD elements with low exposure frequencies, including the elements that are not mentioned in the manuals.For ease of reference, the classifcations used previously for essential and additional elements are listed in Tables 5 and 6.
Te results indicate a clear diference in ODD elements with high and low exposure frequencies.Te analysis of exposure frequencies of ODD elements revealed that similar to the fndings of Capallera et al. [15], most manuals do not clearly communicate the necessary information.Out of 31 manuals analyzed, only 31 out of 110 essential ODD elements were explicitly mentioned in more than 16 manuals.

Analysis of ODD Presentation in Manuals.
Te presentation of ADAS-related ODDs in manuals was investigated.Te manuals selected for the analysis were those that specifed more than 55 of the 110 essential ODD elements summarized in Table 2.
Te ODD can be presented as the following four primary approaches: (1) specifying the operating conditions, (2) expressing through "warning" and "caution" remarks, (3) organizing the "limitations" section, and (4) explaining situations in which ADAS functions cannot be operated within the purview of its description.
First, the operating conditions described in the manual of the Accord Hybrid Touring of Honda Motors were Note.V2V: vehicle-to-vehicle; DSRC: direct short-range communication; GPS: global positioning system; 3D: three-dimensional.6 Journal of Advanced Transportation  Journal of Advanced Transportation analyzed.Tis method describes a situation in which ADAS functions can be operated and are familiar to drivers.However, this presentation method mentions only those ODD conditions that can be operated and does not describe situations or restrictions that may be dangerous when using the ADAS functions.Second, the manuals of the Audi S8L, Porsche 911 Turbo S, Hyundai-Kia Universe, and BMW Series 7 that correspond to expressing "warning" and "caution" remarks were examined.Tis method primarily expresses the limitations of ADAS and the dangerous situations that may occur during driving.However, as the warning is written as "may not work" and the method does not correctly describe the ODD, drivers cannot easily recognize the ODD.

Journal of Advanced Transportation
Tird, the manuals of the Hyundai G80 corresponding to organizing the "limitations" section were considered.Herein, drivers can easily recognize and understand the ODDs as they are organized using ADAS technology.However, the relevant section vaguely specifes the ODD as "the elements that infuence include, but are not limited to, the following." Finally, the manual of the Daimler Truck E3 Cayenne Turbo was analyzed.In this method, drivers can recognize an ODD and the limitations of the ADAS functions under the premise that they are capable of completely understanding all function descriptions.However, the ODD of ADAS is vaguely specifed in this method and the description of the technology is prioritized over its technical limitations.Figure 1 depicts examples of the aforementioned four methods.
Te aforementioned presentations indicated that most manuals explain the ODD based on "warning" and "caution" remarks.Te frst presentation method explained the ODD in the most comprehensible manner as it was described in a separate section after the function description of the ADAS and comprised more ODD-related information than the other methods.However, the majority of limitations are presented ambiguously with phrases such as "can be used," "may not be," and "may not operate."Tis could lead to difculties in clearly recognizing the situations in which ADAS can function.

Summary.
Te essential and additional elements of ODD were identifed by performing ODD classifcation.Furthermore, the exposure frequency of ODD elements and presentation methods were analyzed.
Te analysis indicated that vehicle manufacturers are attempting to present the ODDs of ADAS to drivers using Journal of Advanced Transportation various methods.Te analysis of ODD presentation reveals that the presentation of ADAS's ODD is often couched in ambiguous terms regarding limitations and performance, with phrases such as "can be used," "may not operate normally," and "may operate unexpectedly."Furthermore, the inconsistency in ODD presentation and the representation of ODD limitations are likely to cause confusion among ADAS users, as indicated in [1,9].
In conclusion, the manuals contain only a few of the essential ODD elements, which are not presented clearly to enable drivers to recognize the ODDs.Terefore, a standard method for presenting ODDs in the manuals must be established to ensure that drivers can easily recognize the operational limitations of ADAS functions in terms of ODDs.

ODD Presentation Guidelines for Improving ADAS Safety.
Te ODD presentation guidelines for ADAS-equipped vehicles were obtained based on the trend analysis of ODDrelated regulations for ADSs.Subsequently, ADAS-related ODD presentation guidelines for manufacturers, governments, and consumers were determined.

Trend Analysis of ODD-Related Regulations for ADSs.
Te commonalities and diferences in the ODD-related regulations enacted in Europe, the United States, and Korea were analyzed.

ODD Legislation Trend in Europe. Te European
Union requires AVs to be driven in the operational domain (OD) while considering road conditions, geographical areas, environmental conditions, and speed ranges.In addition, vehicle manufacturers should provide AV users with information on the operational conditions of the system, OD scope, and functional limitations in an easily understandable format [17].

ODD Legislation Trend in the U.S.
A policy introduced by NHTSA in 2016 [12] specifes that manufacturers and the Department of Transportation should clearly specify ODDs, including the roadway type, geographical location, speed range, lighting conditions for operation, and weather conditions.Additionally, the manuals provided by manufacturers stipulate that the function, performance, and ODD of the ADS must be clearly indicated and the state in which the ADS cannot be operated must be specifed.
A document issued by NHTSA in 2018 [11] specifes that ODDs should be considered when testing automated driving technologies.However, the document is a report that systematically presents experimental examples of automated driving technology and does not serve as a regulation.

ODD Legislation Trend in Korea.
According to Article 111-3 (designation of operable areas for ADSs) of the Korean "rules on the performance and standards of automobiles and auto parts," vehicle manufacturers must specify drivable areas where AVs can be operated.Tese regulations require vehicle manufacturers to specify the driving environment, such as the road and weather conditions, operating limits of the ADS, and other information related to the safe operation of the vehicle in drivable areas.
Additionally, according to the safety standards for partially automated driving systems corresponding to the aforementioned regulations, such systems should respond to the operable area specifed by the manufacturer during operation.Otherwise, the driver must be allotted sufcient time to assume control of the ADS.Te partially automated driving system must automatically adjust the vehicle speed based on environmental conditions to comply with the ODD specifed by the manufacturer.
2.5.5.Summary.Both the European and U.S. regulations state that the documentation provided by the manufacturer must include ODD-related elements of an ADS.Furthermore, a defnition of ODDs must be provided in Europe, the U.S., and Korea along with the elements to be included, such as the roadway type and weather conditions.However, unlike in Europe and the U.S., no regulation has been established in Korea that requires ODD-related elements to be included in the documents provided by manufacturers.Furthermore, drivers are not mandated to recognize and focus on the limitations of automated driving technology.Terefore, similar to the European and U.S. regulations, the content must be presented in Korean laws and regulations, which will enable vehicle manufacturers and drivers to easily recognize the functions and limitations of automated driving technology.

Guidelines for ADAS-Related ODD Presentation.
Vehicle manufacturers must efciently communicate the capabilities and limitations of ADAS to drivers.However, the analysis of the ODD presentation indicated that the essential ODD elements suggested by various organizations are not clearly presented.Although various countries follow certain regulations for specifying the ODD in the manuals, they are not yet standardized.In other words, manufacturers fail to clearly present the items to be specifed because of ambiguous rules and the responsibilities of manufacturers and consumers are not easily distinguished.As consumers do not possess a clear understanding of ADAS and may not be aware of its limitations, trafc accidents may occur when ADAS technology is used in situations where its utilization is not feasible.Terefore, this section proposes ADAS-related ODD presentation guidelines for manufacturers, governments, and drivers.
2.6.1.Guidelines for Vehicle Manufacturers.Te ODD presentation guidelines for vehicle manufacturers can be summarized as follows: Guideline 1: in the user manual, the vehicle manufacturer must specify a certain classifcation based on ADAS functions to clearly present the purpose of their use and facilitate understanding Guideline 2: the vehicle manufacturer must clearly present the ADAS functions, limitations, and ODD in the user manuals in the formats presented in Tables 7  and 8 Guideline 3: when ADAS cannot be implemented owing to the failure of vehicle equipment or system errors, the vehicle manufacturer must inform the driver of the newly restricted ODD via HMI Typically, ODDs are presented in two formats (Tables 7  and 8).However, the vehicle manufacturer may modify the format, if required, to ensure convenience to drivers.As specifed in the guidelines, vehicle manufacturers should aim to explain the ADAS functions, limitations, and ODDs as clearly as possible in the user manuals in the recommended formats.
Most user manuals present the ADAS functions comprehensively.However, only a few methods are available for delivering an ODD for each function.Terefore, the format presented in Table 7 can be used to verify the ODD of each ADAS function installed in the vehicle.Tis enables the verifcation of essential and additional ODD elements based on the ADAS function.Table 7 presents the essential and additional elements of the subcategory "roadway type" from the primary category "physical infrastructure."Four key ADAS technologies in the driving-safety feld of the Hyundai Motor G80 are selected as examples.
Table 7 summarizes the manner in which the individual functions of the ADAS operate for each ODD element.An ADAS function operating in the entire environment in a manner that corresponds to a certain ODD element is indicated by "O."If a function operates only in certain environments and does not operate in any environment, it is indicated by "△" and "X," respectively.However, in Table 7, only "△" and "-" are indicated because the ODD presentation is not clearly described in the Hyundai G80 user manual; here, "-" is used to denote the absence of an explanation (Table 7).
Considering an example from Table 7, if the curvature of a curve is extremely large or small, a navigation-based smart cruise control (NSCC) system may not function as intended.
Table 8 may be used to describe individual ADAS functions to convey the contents presented in Table 7 more efectively; this format can be placed at the bottom of a section in a user manual.Tis format provides easily comprehensible and specifc examples of driving and nondriving situations based on the method used by BSI.Additionally, the familiarity of the format to consumers ensures that ODD-related information can be easily recognized.Table 8 presents an example prepared based on forward collision-avoidance assist, which is an ADAS function of the G80 of Hyundai Motors.After analyzing the user manual, only the essential elements of "physical infrastructure" are presented to indicate both driving and nondriving situations.Although the manual of Hyundai's G80 contains a few ODD-related elements, it does not ofer high specifcity; therefore, the ODD must be presented in more detail than the example presented in Table 8.
Te AVs restrict the ADAS functions when traveling outside the ODD, which should be informed to the driver.Terefore, HMI should be utilized to ensure that drivers are aware of the functional limitations of ADAS technology and the newly restricted ODD, as suggested in [12,13].

Guidelines for Governments.
Te guidelines for ODD presentation to the government can be summarized as follows: Guideline 4: to rationally promote the stable development of ADAS and driving safety, proposals from various organizations should be considered and the presentation of ODDs must be standardized Guideline 5: relevant laws must be enacted such that vehicle manufacturers can specify the ODD in the manuals and set the format Guideline 6: ensure that consumers are aware of ADAS technology and vehicle performance and are accountable when enacting legislation Guideline 7: campaigns and educational programs should be conducted to beneft the public Te standardization of ODD presentation facilitates the consideration of the opinions of various research institutes and international organizations and enables accountability of both manufacturers and consumers, as presented in the U.S. Vehicle Safety Act.Additionally, considering the Enforcement Rules of the Trafc Safety Act of Korea, the standards for writing manuals can be set in a form similar to the laws proposed for digital tachographs.

Guidelines for Drivers.
Te guideline for ODD presentation to drivers can be summarized as follows.
Guideline 8: drivers should not solely rely on ADAS and must understand its functions, limitations, and ODD by reading the manufacturer's manual.
Several studies have reported that trafc accidents caused by complete reliance on automated driving technology may increase.Terefore, drivers should recognize and focus on the functions, limitations, and ODD when using ADAS technology by understanding the information presented in the user manuals.

Conclusions and Future Research
3.1.Conclusions.Te popularization of low-level automated driving technologies, such as ADAS, has signifcantly reduced trafc accidents.However, in recent years, the number of trafc accidents caused by the complete reliance on automated driving technology and driver negligence has increased.In addition to driver negligence, vague and unclear guidance pertaining to ADAS usage in user manuals also contributes to the aforementioned problem.Terefore, this study presents guidelines for manufacturers, governments, and consumers to increase safety when using the ADAS.
As ODDs are directly associated with the safety of automated driving technology, the trends of ODDs from international organizations were analyzed.After accumulating the concepts and elements of ODDs presented by SAE, BSI, and NHTSA, the essential and additional ODD elements were defned.
A frequency analysis of the ODD elements in the manuals revealed that most manuals specifed approximately 60 ODD elements.Approximately 100 essential ODD elements exist, which must be supplemented.Furthermore, an analysis of the ODD presentation method indicated that most manuals specifed ODD based on three methods; however, the presentation was  vague and unfamiliar to drivers.Terefore, a standardized method for presenting an ODD must be devised to ensure that drivers can easily recognize the limitations of the technology.Guidelines for presenting ODDs have been presented in this paper to beneft manufacturers, governments, and consumers.Manufacturers should efectively communicate the ADAS functions, limitations, and ODDs to consumers via standardized formats.If the ADAS functions are degraded, only a few ODDs should be communicated via HMI.Additionally, the government should reasonably standardize ODD presentation to promote the stable development of ADAS and driving safety.Consumers should not entirely rely on ADAS technology when driving an ADAS-equipped vehicle and should focus on safety.Te consumers should also read the manual to recognize the functions, limitations, and ODD of the technology.
Te levels of ODD provided in the technical documents and manuals of ADAS-equipped vehicle manufacturers were analyzed for situations where the classifcation and items of ODD were not clearly defned.Tis study presents the basic guidelines to prepare for scenarios where ODDs are clearly defned.Te application of the ODD concept to vehicles equipped with ADAS suggested in this study directly afects the driving safety of ADAS-equipped vehicles.

Limitations and Future Endeavors.
As international conventions and concepts pertaining to ODDs are currently being transitioned based on the suggestions of various organizations, the verifcation process for establishing essential and additional ODD elements for each institution is inadequate.Moreover, although the enforceability of the regulations and laws related to ODDs proposed by various organizations difers, the guidelines consider all proposals that present regulations for enacting the laws and regulations.
In this study, the guidelines established based on the enactment of laws and regulations in the U.S., Europe, and Korea were presented.However, the limitations are that the analyzed manuals are 31 manuals of vehicle manufacturers sold in Korea, and despite existing guidelines that suggest the need to investigate the display of ODD restrictions through HMIs, this aspect was not researched.In the future, it is necessary to collect more manuals for various vehicle types and conduct research on presenting, displaying, and standardizing ODDs from various aspects to standardize integrated ODDs.Tis will provide more systematic guidelines for the efective use of ADAS-equipped vehicles.

Figure 1 :
Figure 1: Examples of operation design domain (ODD) presentation.(a) Method of specifying the operating conditions.(b) Method of expressing via "warning" and "caution" remarks.(c) Method of organizing the "limitations" section.(d) Method of explaining situations in which ADAS functions cannot be operated.Sources: manuals of the 2022 Honda Accord Hybrid, 2021 Audi A8, 2021 Hyundai Genesis G80, and 2021 Audi A8.

Table 1 :
Examples of ADAS functions.

Table 4 :
Vehicle models acquired for the analysis.

Table 5 :
ODD elements with high exposure frequencies.

Table 6 :
ODD elements with low exposure frequencies.
Note.DSRC: direct short-range communication; CBD: central business district; VMS: variable message sign.

Table 8 :
ODD presentation format 2. Divided highways, undivided highways, high-occupancy vehicle lanes, one way, private roads, and reversible lanes Undrivable area FCA may not function accurately when driving on on/of ramps, turn-only lanes, intersections, motorways, minor roads, and slip roads Note.FCA: forward collision-avoidance assist.