Young adults in motor vehicle collisions in Norway: user safety errors observed in majority of cases with severe or fatal injuries

This study has documented that safety errors and missing safety equipment in the MVs were present in 59% of the cases when young adults sustained MAIS score ≥2 injuries on Norwegian roads. In addition, it was found that many of the injuries and several fatalities could have been prevented by properly restraining and protecting the occupants using airbags.

A high-energy MVC results in the abrupt deceleration and deformation of the MV, exposing the occupants to a diversity of motions and potential impacts. Severe occupant injuries are almost invariably the result of direct contact to the head or chest. The occupant commonly makes contact with certain parts of the MV interior, such as the windshield, roof, or steering wheel. In some cases, the occupant will receive secondary impacts from moving objects within the MV [13]. The complexity of these movements needs to be considered when assessing the effects of various safety measures. Very occasionally there are reports of unrestrained occupants involved in extremely high-energy MVCs who miraculously survive, sometimes even being able to leave the crash scene without any significant injuries. The protective role of seatbelt use against the risk of most major injuries is well established [14], since this often prevents occupants from being thrown into MV structures or completely ejected from the MV [15]. A meta-analysis of 24 studies from 2000 onward found that seatbelt use can reduce fatal and nonfatal injuries the front-seat occupants by 60%, and fatal and nonfatal injuries in rear-seat occupants by 44% [16].

The present study has revealed that a considerable proportion (33/111, 30%) of the young adults who died or were severely injured were not using a seatbelt. The nine fatalities among these all sustained crush injuries due to impacts to the head or chest. The investigations performed in each case showed that a correctly restrained occupant most likely would have survived the impacts, since there was sufficient space to avoid impacts within the MV. We observed that the risk of MAIS score ≥2 injuries was 3.3-fold higher for unrestrained than restrained young adult occupants, after adjusting for other collision-related factors. This analysis also identified that several unrestrained occupants were fortunate to avoid severe injuries.

Why do young adults continue to drive unrestrained? A report from the World Health Organization suggested they do not use seatbelts for reasons such as the driving trip being short, simply forgetting, or being in a hurry [15]. Bad habits and misunderstanding of the safety effects of seatbelts have also been reported [15, 17, 18]. To complicate matters, young adults (and particularly males) have higher crash rates than other age groups [19], which has led to the increased crash risk being attributed to factors such as brain immaturity, susceptibility to high-risk driving behaviors (e.g., speeding), short driving experience, and DUI [2, 9, 20, 21].

DUI was associated with an almost threefold higher risk of severe injuries. Additionally, nighttime driving and driving on dark roads were independent risk factors for injuries with an MAIS score ≥2. Young adult drivers and passengers commonly combine alcohol consumption with reckless driving, speeding, and not using a seatbelt, which is why they have a higher risk of collisions and injuries during nighttime [7, 9, 20, 21]. Williams also suggested that late-night driving increased the crash risk due to driving being more difficult in darkness, particularly for newly licensed drivers [22]. Public transport is scarce at nighttime in rural areas of Norway, leading young people to drive more for social purposes or for pleasure. Possible preventive measures might include restricting young drivers to certain times of the day or, in particular, certain days of the week. Restrictions on nighttime driving and driving with peer teenage passengers have become part of graduated licensing systems in the USA [23] and New Zealand, and they are showing positive effects [7]. An alternative strategy has shown promising results in Norway, where instead of a graduated licensing system, the age limit for supervised practice is 16 years while the licensing age is 18 years, which gives the learner driver an opportunity to acquire more driving experience before being allowed to drive on their own [24]. Moreover, the especially strict Norwegian penalty point system for young drivers (who are punished with double the number of points in the first 2 years after they have obtained their driving license compared with older drivers) has showed promising results in reducing the risk of injury for young adult MV occupants [25].

The multivariable analysis also revealed associations of MAIS score ≥2 injuries with side impacts and MV deformation. Examinations of the MV interiors revealed that the following elements increased the injury severity during side impacts: improper sitting position, insecure cargo or fellow occupants, not using a seatbelt, improperly tightened shoulder part of the seatbelt, and lack of side airbags and side curtain airbags. Moreover, a reclined sitting position at the time of collision suggested that the occupant was not sitting optimally in relation to the door and B-pillar, resulting in the protective effect of side airbags being suboptimal, as described by previously by others [26].

If the shoulder part of the seatbelt is too loose, it will not tighten effectively across the occupant’s torso during a side impact, increasing the risk of excessive body movements and occupant-to-occupant injury. In two cases, we suspected an injury mechanism where the young adult occupant was injured by the intruding structure but also injured by contact with the adjacent occupant in the same seating row who had their shoulder part of the seatbelt too loose. Both Siegel et al. and Hillary et al. suggested an association between side impacts and increased injury severity [27, 28]. Compared with frontal impacts, seatbelts provide reduced protection in side impacts [29, 30], and occupant-to-occupant contact injuries are reportedly more prevalent [31]. Newland et al. also suggested that occupant-to-occupant injury is probably underreported since there is often little evidence in the MV available to investigators of impacts between two occupants. Those authors also demonstrated that drivers having a restrained front-seat passenger present during near-side impacts had an increased risk of MAIS score ≥ 3 injuries, with the risk further increasing if the passenger was not using a seatbelt [32].

The statistical analysis indicated that some variables were not independently predictive of the injury outcome. Some safety errors were present among both those with and without MAIS score ≥2 injuries, but the in-depth analysis still revealed that these errors had detrimental effects on occupant safety. Overall, misuse of seatbelts, unsafe seating positions, and insecure cargo were errors present for 18 occupants who suffered MAIS score ≥2 injuries. Six of them had the shoulder part of the seatbelt incorrectly routed under the arm, which during a collision increased the upper body and head movements and the pressure against the abdomen, resulting in severe head and abdominal injuries. Another six occupants with MAIS score ≥2 injuries had correctly routed seatbelts but overly reclined seat backs, in some cases where the seat back was nearly horizontal. We concluded that this seat-back position had significantly negative effects due to the seatbelt being loosely positioned across the body, thereby allowing excessive forward and sideways motions during rapid MV deceleration. All of the occupants directly impacted the MV interior. One-third of the occupant-related errors were insecure objects in the rear seat that either directly hit six of the drivers, or hit and displaced their seat backs, thereby increasing the seatbelt loading and occupant injuries.

Furthermore, we found that in 13 cases the MVs were older passenger cars lacking side airbags and side curtain airbags, which probably contributed to the injury severity in side impacts. Such airbags help mitigate impacts to the head, chest, abdomen, and pelvis since they provide coverage of the A-pillar, B-pillar, and side roof rail, and further serve as a containment barrier to prevent partial or complete ejection from the MV [33]. Moreover, older MVs also do not include modern crash-avoidance systems, and 81% of the MVs in the current study were older than 10 years. Høye [37] reported that older MVs in Norway are overrepresented in speeding and DUI crashes, and that male and young drivers are overrepresented in these types of crashes. Young adults are more likely to purchase older MVs since they are cheaper. Future government campaigns targeting young adults and parents should emphasize the importance of driving a modern MV equipped with adequate safety equipment. This should also include seatbelt reminders in the front and rear seats. Manufacturers should also be encouraged to equip their MVs with seatbelt interlock devices to prevent the vehicle from being started unless the occupants have fastened their seatbelts [34].

It is especially noteworthy that 89% of the MVCs occurred in rural areas in the present study. Previous research has also found higher rates of MVC fatalities in nonurban environments [35]. Possible contributory factors such as longer travel distances for rural drivers, more-lax attitudes toward MV safety measures, worse road safety (e.g., no barriers between opposing lanes), higher speed limits, greater alcohol consumption, and longer times to receive medical attention have been highlighted [35, 36].

Strengths and limitations

In-depth investigations of exterior and interior environments of the involved MVs provide far more information about occupant-related factors [37]. However, detailed multidisciplinary studies of real-world MVCs are challenging [9]. We were unable to confirm whether all of the occupants who received MAIS score ≥2 injuries were admitted to hospitals, although we consider this highly likely since occupants with serious injuries would be transported to a hospital, in which case we would have been alerted. One major strength of this study was that experienced collision investigators systematically and prospectively performed the on-scene collection of collision data.

Data obtained from various sources were compared and reviewed by a multidisciplinary team, including assessing seatbelt use or misuse at the time of the collision and the potential severity of other safety errors. The in-depth analyses, photographs, reconstructions of each occupant’s movements inside the MV, and knowledge about the occupants’ injuries provided us with essential detailed data on the factors relevant to MVCs for determining the injury mechanisms. To reduce errors and irregular assessments, data obtained from different sources were compared and reviewed by the same multidisciplinary team. Moreover, data were collected by the same collision investigators, and injury severity scoring was performed in a uniform manner, which should also have reduced the interrater variability. We consider this approach superior to utilizing existing databases.

The small sample of injured occupants with seatbelt misuse, driving with a reclined seat back, or the lack of protective side airbags or side curtain airbags is probably a limitation for identifying these factors as being associated with MAIS score ≥2 injuries. However, the design of the study made us to discover that the injury consequences of such safety errors were severe, and sometimes life threatening.

One limitation of this study is that information about speed and DUI is not always based on exact measurements, and not all occupants involved in the included MVCs were tested for alcohol and drugs. The prevalence of DUI may therefore have been underestimated.

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