1. Introduction

1.1. Necessity of introducing international standards for large size vehicles

In 2019, new international standards were established and implemented to apply various advanced safety devices to medium- and large-sized buses and cargo vehicles to prevent accidents involving pedestrians and cyclists caused by large vehicles. This includes policies to strengthen safety standards for medium- and large-sized vehicles, including passenger cars, by mandating various advanced safety devices such as intelligent speed assistance devices, blind spot detection information systems for medium- and large-sized vehicles, and collision warning systems for pedestrians and cyclists. In addition, it is being operated as a new international standard in cooperation with the World Forum for Harmonization of Vehicle Regulations(WP.29).⁽¹⁾

Recently, in Korea, there has been a need to strengthen the standards by introducing new international standards to prevent accidents caused by drivers of mid- and large-sized vehicles making right turns in their blind spots, and accidents caused by pedestrians and cyclists not being aware of the front, rear, and sides. However, it is difficult to respond preemptively to the introduction of new international standards for mid- and large-sized vehicles in Korea due to the reality that the country relies solely on the domestic market, and considering the development and budget investment and technology development period of new cars. Therefore, in order to introduce new international standards for mid- and large-sized vehicles in Korea, it is necessary to establish and announce a mid-to-long-term roadmap for the domestic introduction of clear international standards by model in stages.

1.2. Status of adoption of international standards in major countries

The European Union is in the process of proposing and preparing international standards necessary for WP.29 to implement safety enhancement policies that mandate various advanced safety devices to prevent traffic accidents, and is actively introducing international standards.⁽²⁾ The United States operates its own standards that are different from international standards, and is actively securing the lead in international standards for advanced automobiles such as autonomous and hydrogen-powered cars, but is expressing reservations or opposition to revisions to other standards.⁽³⁾ Japan is actively proposing and introducing international standards, and is actively investing budget and manpower to reflect the technology of its domestic industry in international standards.⁽⁴⁾ China has recently been actively participating in discussions related to advanced automobiles such as autonomous and hydrogen- powered cars, but is passive in introducing international standards.⁽⁵⁾

In the past five years, 25 new UN standards have been established, 5 new UN GTRs, and a total of 30 international standards have been established, and 640 revisions to existing international standards have been adopted. In particular, 7 international standards have been established, including detection and alarm systems for eliminating blind spots in large passenger and cargo vehicles and ensuring the safety of pedestrians and cyclists in Table 1. Accordingly, it is necessary to consider introducing new safety devices for mid- and large-sized vehicles in Korea and to collect opinions from related manufacturers to prevent accidents caused by mid- and large-sized vehicles.

1.3. International standards introduced in Korea

In order to improve the international consistency of domestic vehicle safety standards, a gradual introduction of international standards applicable to medium and large-sized vehicles that are not reflected in Korea or require revision is being promoted in Table 2.

First of all, the introduction of international standards to strengthen safety focuses on improving passenger protection in the event of safety accidents such as collisions and rollovers.

Accordingly, 11 items are being introduced, including body and seat strength, seat belt strength, and rollover safety requirements for medium and large-sized buses. However, since the introduction of international standards for large passenger vehicles requires a complete change in the vehicle body design and large-scale new investment, it is necessary to conduct an introduction study that considers the technical and economic acceptability of domestic manufacturers in advance.

In addition, the introduction of new safety technologies is being implemented in stages, including eight new international standards, including a vehicle-to-pedestrian automatic emergency braking system, a blind spot detection system, a front pedestrian and bicycle detection notification system, and a large vehicle accident data recorder, along with recently established international cybersecurity and software update standards.

1.4. Purpose

Among the items to be introduced as international standards in Korea, there are no domestic standards for three items for safety enhancement(commercial vehicle cap strength, front underrun protective devices, and direct vision standard of commercial vehicles) and one item for advanced safety technology(moving off information systems for detection of pedestrians).

In this study, we analyzed the Korean In-Depth Accident Study(KIDAS) and the pedestrian and PMV accident data(KIDAS(P)), which are the traffic accident investigation system, to establish basic data that can provide a basis for introducing domestic safety standards (draft) for large size vehicles in Korea.^(6,7)

2. Methods

2.1. Data source

2.1.1. KIDAS database for analysis of large size vehicle occupant injuries

Among the 4,712 data collected from 2011 to 2022, 90 cases of large size vehicles were analyzed. Frequency analysis was conducted for gender, age group, season, weather condition, accident time, kinds of roads, and road type. In addition, injury severity was analyzed using injury data for occupant injuries between the two groups of large vehicles and non-large size vehicles. Statistical analysis was performed using the independent t-test. This study was approved by the research ethics committee of Wonju Severance Christian Hospital, Yonsei University(IRB Approval No.: CR313137).

2.1.2. KIDAS(P) database for analysis of pedestrian and personal mobility vehicle(PMV) traffic accidents

122 pedestrian and PMV traffic accident data collected from September 2023 to November 2024 were used. Frequency analysis was conducted on injury severity, gender, age group, season, weather conditions, accident time, road type, and collision object. In addition, the accident distribution was described for 17 cases of collision with large size vehicles among the total data. This study was approved by the research ethics committee of Wonju Severance Christian Hospital, Yonsei University(IRB approval number: CR324040).

2.2. Data collection

2.2.1. Crash data - Collision Deformation Classification (CDC) code

CDC code is a method proposed by the Society of Automotive Engineers and consists of a total of 7 digits. Each digit indicates the type and severity of vehicle damage. The first and second digits indicate the principal direction of force(PDoF) in a clockwise direction, the third digit indicates the deformation position of the accident vehicle, and the fourth digit indicates the horizontal position of the collision. The fifth digit indicates the vertical position of the collision, the sixth digit indicates the pattern that contributed to the collision, and the seventh digit indicates the degree of vehicle deformation.⁽⁸⁾

2.2.2. Injury data - Abbreviated Injury Score(AIS) and Injury Severity Score(ISS)

AIS is a useful injury scale for classifying the severity of traffic accident patients. It is a simple injury scale established by the Association for the Advancement of Automotive Medicine(AAAM), which is classified into 7 digits and 8 body parts, and assigns injury severity from 1 to 6 points.⁽⁹⁾ AIS 1 is classified as the head and neck, AIS 2 as the face, AIS 3 as the chest, AIS 4 as the abdomen and pelvic organs, AIS 5 as the upper and lower extremities and pelvis, and AIS 6 as external factors such as burns, frostbite, and explosions. MAIS(Maximum Abbreviated Injury Scale) indicates the maximum AIS value among each body part.⁽¹⁰⁾ ISS is calculated by selecting 3 parts with high severity from AIS and calculating the sum of squares as in Eq. (1) .

It is expressed numerically between 0 and 75 points, and a patient with a score of more than 16 points is deemed to be severe with multiple injuries.⁽¹¹⁾

3. Results

3.1. Large size vehicle occupant injuries

3.1.1. Descriptive analysis

Table 3 shows the general characteristics of large size vehicle crashes. Among the 90 cases analyzed, males accounted for 96.7%(87 cases) of all accidents, with the highest occurrence among individuals in their 50s(33.3%). The highest number of accidents occurred equally from March to August(28.9%) and were most frequent during the morning hours(06:00-12:00) under clear weather conditions(32.2% and 46.7%, respectively). The most common road type where accidents occurred was national highways(36.7%). The most common road type where accidents occurred was national highways (36.7%). The most frequently observed severe injury was chest trauma, occurring in 19 cases(31.7%). Among the occupants, 25 cases(27.8%) were classified as severe.

3.1.2. Injury severity

Table 4 shows the analysis of vehicle damage and occupant injury. It was divided into large and non-large size vehicles according to motor vehicle occupants and colliding opponents. Vehicle damage(Crush extent) was significantly higher in large size vehicle crashes(5.36±2.51) than in non-large size vehicle crashes(3.03±2.14, p=0.003). When the colliding opponent was large size vehicle, crush extent was significantly higher(4.08±2.71) than in collisions with non-large size vehicle(2.99±2.10, p<0.001). Also, ISS was significantly higher in large size vehicle crashes(8.99±9.99) than in non-large size vehicle crashes(6.91±9.26, p=0.010).

3.2. Pedestrian and PMV occupant injuries

3.2.1. Descriptive analysis of overall cases

Table 5 shows the general characteristics of pedestrian and PMV crashes. Among the 122 cases analyzed, males accounted for 54.1%(66 cases) and females for 45.9%(56 cases), with the highest incidence occurring among pedestrians aged 70 and above(34.4%). Accidents were most frequent in autumn(39.3%) and primarily occurred during the evening hours(18:00-00:00) under clear weather conditions(46.7% and 35.2%, respectively). The most common accident location was municipal and district roads(70.5%). Among the colliding vehicles, recreational vehicles(RVs) were the most frequent(23.8%), followed by sedans(23.0%) and trucks(13.9%), excluding 10 cases involving PMVs with no colliding vehicle. Regarding injury severity, 59% of cases were classified as minor, 24.6% as severe, and 16.4% resulted in fatalities.

3.2.2. Descriptive analysis when the collision opponent is a large car

Table 6 describes 17 of the 122 pedestrian and PMV crashes in which the colliding opponent was a large size vehicle. Males accounted for 52.9% of these accidents, with individuals aged 70 and above being the most affected(47.1%). The highest number of incidents occurred during the autumn months(September to November) at 47.1%, predominantly during the morning hours(06:00-12:00) and under clear weather conditions (35.3% and 58.8%, respectively). The most common accident location was on municipal and district roads(58.8%), and the predominant type of collision was a frontal crash(58.8%).

4. Discussion

This study aimed to analyze traffic accident investigation data on safety standards for large size vehicles, for which there are no domestic standards yet in Korea, to provide basic data for presenting domestic safety standards for large size vehicles(draft). The related standards covered in this study were three safety enhancement items(commercial vehicle cap strength, front underrun protective devices, and direct vision standard of commercial vehicles) and one item for advanced safety technology(moving off information systems for detection of pedestrians).

4.1. Protection of the Occupants of the Cab of a Commercial Vehicle(R29)

According to the findings of this study, the comparison between large and non-large size vehicles revealed significant differences in crash impact and structural integrity. Most domestic large size vehicles adopted a cab-over design, which resulted in a considerably smaller crumple zone compared to non-large vehicles, increasing the crush extent of vehicle damage upon collision. The severity of vehicle damage raised the likelihood of intrusion into the occupant compartment, thereby increasing the risk of occupant injuries. Furthermore, when the colliding opponent was a large vehicle, differences in weight and structural rigidity further exacerbated the damage and injuries sustained by the impacted vehicle. To mitigate occupant injuries in large size vehicles, reinforcing cab strength or expanding the crumple zone through design modifications should be considered. However, as design alterations might have been unfavorable from a manufacturing standpoint, strengthening cab rigidity appeared to be a more feasible approach. Since this aligned with international regulations, such as the R29 standard for commercial vehicle cab strength, further research in this area was warranted.

4.2. Front Underrun Protective Devices(FUPDs)(R93)

According to the findings of this study, the comparison between large and non-large size vehicles highlighted the potential severity of damage and occupant injuries when a collision involved a large size vehicle. In such cases, preventing the impacted vehicle from being forced into the direction of travel after impact was crucial. In Europe, to prevent passenger cars from underriding trucks in frontal collisions, the ECE R93 regulation was introduced, mandating the installation of Front Underrun Protection Devices(FUPDs) on all trucks starting in August 2003. In South Korea, research has also been conducted on the development of FUPDs, focusing on identifying minimum structural design requirements, evaluating compliance, and establishing assessment criteria.12 This study underscored the necessity of such devices. While international standards, including the R93 regulation, provide guidelines for FUPD implementation, further research is required to assess their effectiveness and applicability in South Korea.

4.3. Moving Off Information Systems for the Detection of Pedestrians and Cyclists(R159) & Direct Vision Standard(DVS) for Heavy Goods Vehicles(R167)

The review of traffic accident cases involving large size vehicles, pedestrians, and PMVs highlighted the importance of securing direct driver visibility. A new UN regulation(provisional UN R167) was adopted by WP.29 in November 2022 to establish visibility requirements for vehicles with over ten passengers(M2, M3) and trucks exceeding 3.5 tons(N2, N3), aiming to minimize blind spots.

Additionally, in October 2022, during the 14th Autonomous Driving Expert Panel meeting, Germany proposed the development of an Urban Emergency Braking System(UEBS) to protect pedestrians and cyclists in low-speed urban environments(0-20 km/h). The initial proposal suggested a system capable of detecting stationary pedestrians and cyclists in front of the vehicle, as well as those crossing at speeds below 5 km/h, issuing collision warnings to the driver and automatically stopping the vehicle. The system was designed to alert the driver upon detecting pedestrians or cyclists at test speeds of 5 km/h and 20 km/h before initiating a vehicle stop. Compared to UN R159, which was established in June 2020 and focuses on pedestrian detection, the newly proposed regulation introduces an automatic stopping mechanism to prevent collisions when a pedestrian is detected approximately 1.67 meters ahead of the vehicle.

In this study, both front and rear collision cases involving large size vehicles and pedestrians revealed that the driver failed to recognize the pedestrian before impact. These findings emphasize the need for further research to develop preventive measures. Moreover, as the use of personal mobility devices continues to rise, future studies should also consider their integration into vehicle detection and safety systems.

5. Conclusion

Through this study, we identified the primary injury sites and types of injuries for occupants of large size vehicles, and we found that the injury severity of occupants in large vehicles is higher than that of occupants in non-large size vehicles. This is a simple comparison that excludes factors such as road conditions and vehicle safety features; therefore, additional research is needed to aid in the introduction of safety standards for large vehicles that align with international guidelines.