Global, Regional, and National Burden of Road Injuries from 1990 to 2019

(1) Background: Understanding occurrence can help formulate effective preventative laws and regulations. However, the most recent global burden and road injuries (RIs) trends have not been reported. This study reports the burden of RIs globally from 1990 to 2019. (2) Methods: RIs data were downloaded from the Global Burden of Disease 2019. Incidence, deaths, and disability-adjusted life years (DALYs) described the trend and burden of RIs. We calculated age-standardized rates (ASRs) and estimated annual percentage change (EAPC) for the above indexes to evaluate the temporal trend of RIs. We evaluated the social-demographic index (SDI) with epidemiological RI parameters and reported proportions of age-standardized rates due to RI. (3) Results: In 2019, the global incidence of RIs reached 103.2 million. The EAPC of RI incidence increased, whereas deaths and DALYs decreased. Age-standardized incident rate (ASIR) was highest in low-middle SDI regions, age-standardized death rate (ASDR) was high in middle SDI regions, and age-standardized DALYs increased in low SDI regions. The highest accident rates were found in those aged 20–24 years old. Cyclist injuries were the leading RIs (34%), though pedestrian and motor vehicle accidents were the leading cause of death (37.4%, 37.6%) and DALYs (35.7%, 32.3%), respectively. (4) Conclusions: Over the past 30 years, RIs incidence increased annually, though death and DALY rates decreased. RIs places a considerable burden on public health in low SDI countries. Data should be used to develop and implement effective measures to reduce the burden of RIs.


Introduction
Recently, road safety has raised many concerns. The UN High-Level Meeting on Global Road Safety, held in 2022, reported the annual global burden of road injuries (RIs) to be 1.35 million deaths and 50 million physical injuries and disabilities [1][2][3]. In large-scale car accidents, the victims of RIs vary, including vehicle drivers, cyclists, pedestrians, and motorcyclists [4]. Road traffic accidents (RTAs) are the primary cause of death in people aged 5-29 years old [5]. In 75 developing countries, reports predict that by 2030 there will be 3 million deaths and 7.4 million injuries and disabilities following severe RTAs in people aged 10-24 years old [6]. Older age, female sex, and lower income status, combined with post-traumatic stress disorder, are factors associated with more severe RIs [7].
Moreover, lower limb RIs are associated with a lower quality of life [8]. RIs are divided into five subtypes: pedestrian injuries, cyclist injuries, motorcyclist injuries, motor vehicle injuries, and other road injuries. Furthermore, in some developing countries, neurotrauma caused by the five RI subtypes accounts for approximately 79% of all neurosurgical patients [9]. Moreover, the highest incidence for all five RIs subtypes is found in those aged 20-29 years old [9].
A global status report showed no significant decrease in RI death rates between 2010 and 2016 globally; however, RI death rates in African and low-income countries increased Focusing on the level of the five SDI regions (Table 1 and Figure 1A), the low-middle SDI region had the highest RI incidence among SDI regions in 1990, which was initially 15.0 [14.6-20.1] million but increased two-fold to 31.1 [25.8-37.0] million in 2019. However, the low SDI region, calculated by the absolute number, had the highest change rate of +132%. The RI incidence rate of the high SDI region significantly decreased by 16.7% from 8.34 [7.33-9.49] million in 1990 to 7.45 [6.43-8.61] million in 2019. The ASIR was significantly decreased in the high/high-middle SDI regions and increased in the other three SDI regions. Interestingly, the ASIR of low-middle SDI regions (1,443. 53   .09], respectively. The EPAC in these SDI regions showed Focusing on the level of the five SDI regions (Table 1 and Figure 1A), the low-middle SDI region had the highest RI incidence among SDI regions in 1990, which was initially 15.0 [14.6-20.1] million but increased two-fold to 31.1 [25.8-37.0] million in 2019. However, the low SDI region, calculated by the absolute number, had the highest change rate of +132%. The RI incidence rate of the high SDI region significantly decreased by 16.7% from 8.34 [7.33-9.49] million in 1990 to 7.45 [6.43-8.61] million in 2019. The ASIR was significantly decreased in the high/high-middle SDI regions and increased in the other three SDI regions. Interestingly, the ASIR of low-middle SDI regions (1,443. 53  Among GBD regions (Table 1 and Supplementary Materials Figure S1A), the absolute incidence of RI increased, with the highest incidence observed in 2019 in South Asia (43,565,410 [35,693,282-52,454,188] Figure 1B). The number of deaths increased in men but decreased in women ( Figure 1B). ASDR changed globally from 21.92 [20.65-23.86] in 1990 to 14.99 [13.29-16.32] in 2019 per 100,000, with an EAPC of −1. 29. In contrast to the number of deaths, the ASDR in men and women was 22.79 [19.37-25.11 [15.32-19.13]). As can be seen in the curve, similar to the global decrease, ASDR in all five SDI regions decreased over time (Table 2).
For GBD regions (   The absolute number for rate of incidence increase (%). Western Europe (a) and the high-income Asia Pacific region (b) with lower ASIR; South Asia (c) and Eastern Europe (d) with a higher ASIR. Western Europe (e) and the high-income Asia Pacific region (f) with lower ASIR-EAPC; central Latin America (g) and East Asia (h) with higher ASIR-EAPC. Most of Western Europe (i) and some of the high-income Asia Pacific region (j) with a lower increase in incidence; North Africa and the Middle East (k) and central sub-Saharan Africa (L) with a higher increase in incidence.  (Table 3 and Figure 1C). The number of DALYs between women and men has not significantly changed over the past three decades.   (Table 3).

Correlation between SDI Index and EAPC
Overall, age-standardized incidence rate does not correlate with the tendency index (EAPC) globally (R = 0.3, p > 0.05). For regions with different SDI indexes ( Figure 3A,B), countries with low SDI indexes have a negative relation to the EAPC (ASIR) (R = 0.54, p < 0.05). In research on the association between the EAPC and ASDR/SDI ( Figure 3C,D), the results are similar to RI incidence; there was no relationship between the 2019 agestandardized death rate and the EAPC from 1990 to 2019 (R = 0.43, p > 0.05). However, in countries with a higher SDI index, the EAPC rate decreases. Notably, there is a positive relationship in the regression model between EAPC and age-standardized DALYs ( Figure 3E,F). Countries with higher age-standardized DALYs have a higher EAPC (R = 0.55, p < 0.05). Evaluation of the correlation between SDI and EAPC showed high SDI regions or countries have stronger negative correlation rates (R = 0.58, p < 0.05).

The Features of RIs in Different Age Groups
We explored the age-related population metric in different genders. In 2019, as shown in Figure 4A, the incidence of RIs was mainly observed among people aged 20-24 years old. This was the same for both women and men. Over the years, a decreasing RIs tendency was seen in men, whilst the incidence rate remained high in women except in women aged over 60, where RIs tendency decreased. Absolute RIs numbers were also lower in women than in men. The death rate ( Figure 4B) presents a similar curve that decreases alongside age increases (though not for people younger than 19 years old). There is a smooth curve for those aged 20-50 years old. Similarly, the death rate in women is lower than in men. Interestingly, the DALYs rate ( Figure 4C) in both genders is different to incidence and death rate. In women, the DALYs rate peaks in the 70-74 age group rather than in the 20-24 age group with the maximum incidence rate. In men, this is different; the peak rate occurs in the 20-24 age group, though with increasing age the DALYs rate steadily declines. However, there is a considerable gap between the genders. Furthermore, when calculating the DALYs rate in the past 30 years, excluding gender differences, people < 19 years old show different conditions. Here, results showed that the difference between 1990 and 2019 in the 20-24 age group was the largest among all age groups in terms of calculated incidence rate (Figure 4D), and the death rate was lower in 2019 than in 1990 in all age groups. This suggests that, with increasing age, the difference in death rate between 1990 and 2019 became more significant ( Figure 4E). When comparing the different DALYs rates, a large difference is seen in the 20-24 age group ( Figure 4F).

The Features of RIs in Different Age Groups
We explored the age-related population metric in different genders. In 2019, as shown in Figure 4A, the incidence of RIs was mainly observed among people aged 20-24 years old. This was the same for both women and men. Over the years, a decreasing RIs tendency was seen in men, whilst the incidence rate remained high in women except in women aged over 60, where RIs tendency decreased. Absolute RIs numbers were also lower in women than in men. The death rate ( Figure 4B) presents a similar curve that decreases alongside age increases (though not for people younger than 19 years old). There is a smooth curve for those aged 20-50 years old. Similarly, the death rate in women is lower than in men. Interestingly, the DALYs rate ( Figure 4C) in both genders is different to incidence and death rate. In women, the DALYs rate peaks in the 70-74 age group rather

The Proportion of Five Different Subgroups of Road Injuries
Observing the incidence of RIs globally, cyclist road injuries (34%) and motor vehicle road injuries (24.8%) account for the majority of RIs. In the high SDI region, the proportion of motor vehicle injuries increased from 19.6% to 46.2% in 2019; however, cyclist injuries decreased from 40.9% to 25.4% ( Figure 5A). when calculating the DALYs rate in the past 30 years, excluding gender differences, people < 19 years old show different conditions. Here, results showed that the difference between 1990 and 2019 in the 20-24 age group was the largest among all age groups in terms of calculated incidence rate ( Figure 4D), and the death rate was lower in 2019 than in 1990 in all age groups. This suggests that, with increasing age, the difference in death rate between 1990 and 2019 became more significant ( Figure 4E). When comparing the different DALYs rates, a large difference is seen in the 20-24 age group ( Figure 4F).

The Proportion of Five Different Subgroups of Road Injuries
Observing the incidence of RIs globally, cyclist road injuries (34%) and motor vehicle road injuries (24.8%) account for the majority of RIs. In the high SDI region, the proportion of motor vehicle injuries increased from 19.6% to 46.2% in 2019; however, cyclist injuries decreased from 40.9% to 25.4% ( Figure 5A). The other four subtypes of injuries showed no apparent difference among the five SDI regions. In GBD regions, the pattern varies. Pedestrian road injuries account for no more than 30% of RIs. In three sub-Saharan African areas, pedestrian injuries rank in the top three among the five injury types. Motorcyclist accidents among GBD regions show a significant difference, with tropical Latin America and Southeast Asia accounting for 35.6% and 37.6%, respectively, making motorcyclist-related RIs the most common in those regions. Motor vehicle injuries make up the majority of RIs in most areas, accounting for over 50% in some regions (Australasia: 51.2%; Eastern Europe: 51.2%; high-income Asia Pacific: 59.7%). In contrast, motor vehicle-related RIs account for just 10.1% of RIs in tropical Latin America.
Focusing on deaths caused by RIs ( Figure 5B), the global death rate for pedestrians in terms of RIs (37.6%) is equal to that of motor vehicles (37.4%). However, the cyclist accident group only accounts for 5.4% of all RIs deaths, even lower than the motorcyclist accident group. Among the five SDI regions, the deaths vary. In the highest SDI index region, motor vehicle accident RIs are the highest cause of death (58.9%); this proportion is also highest when compared to the other four regions in terms of motor vehicle accident RIs. We also focused on the GBD areas related to motor vehicle accidents and found that the tendencies in high-income North America and the high-income Asia Pacific region were contradictory. In the former region, this subtype leads to 69.7% of deaths, while in the latter region they only account for 31.7% of deaths. Motorcyclist accidents influence the death percentage differently, similar to tropical Latin America (34.4%) and Southeast Asia (34%) where this subtype accounts for a large number of deaths. Interestingly, though the incidence of cyclist RIs is high in many GBD regions, the rate of deaths caused by cyclist RIs ranks bottom among the five injury subtypes. The other four subtypes of injuries showed no apparent difference among the five SDI regions. In GBD regions, the pattern varies. Pedestrian road injuries account for no more than 30% of RIs. In three sub-Saharan African areas, pedestrian injuries rank in the top three among the five injury types. Motorcyclist accidents among GBD regions show a significant difference, with tropical Latin America and Southeast Asia accounting for 35.6% and 37.6%, respectively, making motorcyclist-related RIs the most common in those regions. Motor vehicle injuries make up the majority of RIs in most areas, accounting for over 50% in some regions (Australasia: 51.2%; Eastern Europe: 51.2%; high-income Asia Finally, the indication of DALYs shows a similar pattern to deaths caused by RIs ( Figure 5C). Globally, the descending order of DALYs in terms of subtype is motor vehicle (35.7%), pedestrian (32.3%), and motorcyclist (21.9%). In high SDI regions, the majority of DALYs are caused by motor vehicle RIs (58.2%), and this trend is also seen in low SDI regions (42%). Pedestrian injuries cause the highest rate of DALYs in low SDI regions (36.2%), but the lowest rate in high SDI regions (18.8%). The lowest DALYs caused by motorcyclist injuries occur in low SDI regions, while the number is higher in low-middle SDI regions. In GBD regions, southern sub-Saharan Africa (61.5%), high-income North America (65.7%), and Australasia (60.9%) are the top three in terms of DALYs owing to motor vehicle RIs. Interestingly, motor vehicle RIs in all regions occur at a rate of over 30%. In East Asia and Andean Latin America, 48.5% and 40.5% of DALYs are attributed to pedestrian road injuries. This trend decreases in Australasia (14.6%) and high-income North America (15.7%). DALYs caused by motorcyclist crash-related RIs differ, with this subtype accounting for 40.8% in Southeast Asia, 39.6% in tropical Latin America, and just 4.3% in southern sub-Saharan Africa.

Discussion
RIs can severely impact personnel and society [4]. Therefore, in this study, we describe the global burden of RIs in different regions, including quinquepartite SDI regions, GBD regions, and countries/territories from the GBD 2019 database. The results show that the incidence of RIs did not continually increase during the 2000-2005 period (where the global incidence rate is at a plateau). After 2010, RI incidence declined annually; therefore, this period is viewed as the 'Decade of Action for Road Safety' [2]. There may be various reasons that can account for this phenomenon, including global road improvements [22,26,[36][37][38], related legislation implementation [13,22,24,39], and the state of war [40]. The absolute number of RI incidences was highest in India (low-middle SDI region), and the highest numeric RIs value was observed in South Asia. This point has been verified in many previous studies [25,26,34]. After age normalization, the condition varies. India, Pakistan, and Bangladesh belong to the low-middle SDI region, and South Asia has the highest incidence number; however, Russia (high-middle SDI) ranks top in terms of calculated ASIR. The EAPC in Portugal and all high-income Asia Pacific countries (high SDI region) mostly decreased, indicating an increasing reduction in RIs incidence. Moreover, this suggests that effective measures should be implemented to prevent road accidents [13]. We also observed that the RIs incidence rate in men was continuously higher than in women, especially in the 20-24 age group. As traffic laws and medical care improved, the death rate in all regions decreased annually, with an EAPC of −1.29. Up to 2019, the highest two absolute death numbers were observed in China (middle SDI) and India (low-middle SDI). After age normalization, the Central Africa Republic in central sub-Saharan Africa had the highest ASDR, and Singapore in the high-income Asia Pacific region had the lowest ASDR. This suggests that some African regions still need to implement measures to prevent deaths caused by RIs [11,26]. Regarding differences in gender for deaths caused by RIs, similar to what has been observed in previous incidence research, the RIs death rates in men were higher than in women. A potential explanation for this may be that, with increasing age, the physical condition of men declines more rapidly than women [39,41]. Additionally, some economic and social factors should be considered, such as the exposure level restricted by regional legislations [42] and levels of occupational-related mobility [43]. It is also worth noting that a higher amount of driving-related worry and a more robust level of self-control have been postulated to explain women's underexposure to driving [44,45].
The change in DALYs indicated by the results demonstrates that diseases burden public health in across regions. DALYs refer to disability-adjusted life years, which integrates the years of life lost and the years lived with disability [15,16,28]. Among all the SDI regions, the DALYs rate continually decreased. The low SDI region had a higher DALYs rate than the other four regions, especially after 2010, in which most middle SDI regions issued related laws to prevent RIs. Low SDI, low-middle SDI, and middle SDI regions present similar AS-DALYs during the 1990-2010 period in total and/or in men. Conversely, in women, the DALYs rate remains higher in low SDI regions than in other regions. In 2019, the highest DALYs absolute value was observed in India (South Asia, low-middle SDI). After age normalization, the Central African Republic (central sub-Saharan Africa, low SDI) had the highest DALYs rate, indicative of a serious situation in some African countries. In some developed countries such as Singapore (high-income Asia Pacific, high SDI), the AS-DALYs rate is only one-eightieth of the rate in the Central African Republic. Results show that some of the measures taken in some South Asian countries and high-middle SDI regions are making great progress in reducing the burden of RIs with an associated EAPC of −2.4, which is a three-fold improvement when compared to low-middle SDI regions (−0.59).
The results suggest low-middle SDI countries are in an awkward position; on the one hand, they need to build more roads to promote development, and on the other hand, increasing accident burden hampers economic growth. Though their death rate and DALYs rate are even lower than the low SDI region, low-middle SDI countries (such as India) have the highest number and age-normalization rate when calculated by incidence. In India, the RIs incidence rate is not low, owing to India having the second-largest population in the world. The situation is difficult for most low-middle SDI countries; though the speed of increase in RIs incidence is lower (ASIR-EAPC), the rate of decreased deaths (ASDR-EAPC) and DALYs (AS-DALYs-EAPC) remains lower than in the other four SDI regions. This phenomenon appears obviously in South Asian countries [26]. Low SDI countries have a higher ASDR and number of AS-DALYs compared to low-middle SDI countries. We should consider that the medical level in some low SDI regions still represents a public health problem, which has been observed in some African countries [3,11]. Thus, in most low SDI countries, the burden of RIs is still huge. Due to economic development and road conditions in less developed countries, the overall speed of various vehicles may be slower than those in more developed countries, such as middle and high-middle SDI regions (e.g., China, Russia). Hence, when traffic accidents occur, the accidents in middle SDI regions are more severe, causing more deaths and DALYs than accidents in low-middle SDI countries [25,34]. For some middle SDI countries, though the government can afford the economic loss of RIs, the EAPC in ASIR is still higher than even some low-middle SDI countries. Taken together, the conditions in low-middle SDI regions suggest a cautious approach to the prevention of RIs; for those in low-middle regions that develop towards a higher SDI index, low-middle SDI regions could be an example when balancing economic considerations and road injury prevention [7].
Furthermore, whilst non-adults (aged < 19) are not allowed to drive a vehicle in most regions, they can physically move or chase one another more casually [5,46]. In our study, we conclude that the incidence of RIs increases with increasing age. However, the number of deaths related to RIs is low for those under the age of 14. However, there is a sharp shift in the curve of fatalities for those in the 15-19 age group. A study from China shows that RIs were one of the most common causes of death in children aged 5-19 years old and ranked just after neoplasms [47,48]. This can be explained by the fact that legal guardians take care of their children, especially those under 14. However, adolescents change physically and psychologically, including stages of teenage rebellion, translation to maturity while lacking social knowledge, exposure to alcohol, cocaine, and other psychotropic drugs, violent tendencies, and a lack of guardian supervision, all of which increase adolescents' risk of RIs. As such, many studies appeal for the implementation of legislation to protect the safety of children and adolescents [5,49]. Based on our study findings, current legislation has been successful. Compared to 1990, the incidence of RIs for those aged <14 years old was even lower in 2019 than in past decades. Though incidence in the 15-19 age group remained higher than in 1990, the increase in rate is lower than in the adult group. Apart from the decline in incidence, the death rate and DALYs rate were all lower than in other age groups at all times. These data show the effectiveness of these legislations. Moreover, among the elderly, though the incidence rate among older adults negatively relates to age, the death rate/number maintains a high level. This phenomenon can be easily explained by the aged group being more vulnerable to external violence injuries owing to comorbidities and aging organs [39,41].
In general, RIs include five subtypes of injuries. We observe that different regions have different RIs subtype features. In Australasia, Eastern Europe, and high-income North America (countries and territories with a high SDI index), motor vehicle RIs occur more frequently. In tropical Latin America and South Asia, motor vehicle accidents occur the least. Notably, among all the regions, cyclist accidents happen most often. Though the incidence of cyclist accidents is high in most countries, the associated death rate and DALYs rate for this subtype in these regions account for only a small percentage of each metric. Taking eastern sub-Saharan Africa as an example, the incidence rate proportion reaches 50%, yet deaths and DALYs associated with this subtype only account for up to 5.6% and 9.9%, respectively, of the total metric. This abnormality can be explained by the following. Firstly, cyclists typically travel shorter distances and are equipped with fewer protections, which can explain the high incidence rates. Secondly, bicycles cannot travel with the same high velocity as motor vehicles, and this can help limit the severity of a collision. Thirdly, in countries and territories with more extreme climates and environments (such as tropical Latin America), there are fewer motor vehicles on the roads, reducing the severity of collisions between cyclists and motor vehicles [4,50].
Finally, the second subtype of injuries to address is motor vehicle accident RIs. Motor vehicles derive from several industrial revolutions. The number of vehicles in certain regions depends on the natural environment and economic development [13]. The incidence of RIs, deaths related to RIs, and resulting DALYs in high SDI regions or some developed countries remain at a high level. This has caused many governments to enact road laws to decrease the burden on entities [51,52]. Some accidents occur among different transportation forms, such as vehicle-pedestrian accidents [49,50,52] and vehicle-cyclist accidents [1, 6,50]. In such accidents, pedestrians are more vulnerable to loss of life and disabling injuries, especially in older adults and children [5,7,23,39,49]. Our analysis results agree with these existing reports. East Asia and Andean Latin America have the most severe RIs burden on pedestrians, with deaths/DALYs exceeding 50% deaths. Hence, some laws aim to not only reduce the incidence of motor accidents but also provide a level of protection for pedestrians [20,49,52]. Therefore, regardless of the world group division, RIs differ. In developed countries, more pedestrian-motor vehicle injuries cause more deaths. In undeveloped countries, a higher absolute number of vehicles typically increases RIs incidence and death among pedestrians. Road injury is a multifield issue. The use of helmets and seat belts [53], drink driving bans [54,55], speed limitations [56], and restrictions on children's usage of transport have been proven to reduce mortality by 20-40% [2]. Such approaches are critical to low-and middle-income nations, which account for more than 90% of annual road traffic fatalities and incidents [2,3]. As previously reported, certain African countries without helmet-related laws should implement helmet use policies to reduce RIs related to motorcycle crashes [53]. We recommend that legislation in low SDI regions and low-middle SDI regions be further developed around these four elements. Another solution is to improve road conditions by strengthening them, through implementation of cycle tracks [57,58] or through the addition of adequate street lighting [59]. It should be highlighted that the illumination element is still debatable and will need to be verified further in future investigations [59,60].
This investigation also has some limitations. The data from the GBD database were calculated using estimation and mathematical modeling, which can be affected by adjusted and confounding factors. Additionally, different healthcare diagnosis systems in various countries can provide a mistaken impression of incidence and death rate in the region through overdiagnosis and mistaken diagnosis. We also describe global cohort changes in this study but lack gender stratification studies. Hence, further research will investigate gender-related changes in RIs. Some risk factors that cause RIs are not included in this study. In a further study, we could explore the risk factors associated with RIs globally.

Conclusions
RIs remain a concern in many countries and territories. Globally, incidence decreased during the 2010-2015 period, after which the incidence increased to 103.2 million [86. 9-121.3] in 2019. Low-middle SDI countries showed higher incidence levels (31. For GBD regions, there is still a considerable burden on East Asia, South Asia, and sub-Saharan Africa in terms of RIs incidence rates, death rates, and DALYs rate, with a lower EAPC in the decreased indicators. High-income countries suffer less RIs burden, calculated by incidence, deaths, and DALYs, and can reduce the influence of RIs more quickly. Results show that men are more vulnerable to RIs, whatever the economic condition. People aged 20-24 are the leading victim group, though deaths are not highest in this group, owing to their robust recovery. Men over 20 years old have less RIs and DALYs with increasing age, though incidence and the DALYs rate remain high with increasing age in women.
Given both economic and environmental differences, the subtypes of RIs manifest differently in each region. Even though cycling injuries are most common worldwide, they are associated with fewer casualties and DALYs. Countries with a higher incidence of motor vehicles injuries, such as in Australasia, will likely see an increase in the proportion of motor accident deaths and DALYs. Tropical Latin America has more motorcyclist accidents. Consequently, the number of motorcyclist fatalities has become a significant percentage of all RIs. However, pedestrian RIs remain an enormous burden on governments. As such, we recommend that administrators pay more attention to these issues and develop regulations that protect pedestrian safety. Regardless of the type of RIs, we appeal to the use of helmets and seat belts, restrictions on children driving, and the prohibition of alcohol consumption.