The price of personal mobility: burden of injury and mortality from personal mobility devices in Singapore - a nationwide cohort study

Personal mobility devices (PMDs), such as skate-scooters, and motorized personal mobility devices such as electric bicycles (e-bikes) or motorised scooters (e-scooters) have rapidly increased in popularity globally. There has been a corresponding rise in PMD-related injury [1‐5], with unusual injury patterns being described [1, 6], particularly with hoverboards [7‐11].

Motorised PMD (MotPMD) users, in particular, appear to be at greater risk of injury [5, 12, 13]. Reasons proposed include greater risk-taking behaviour for MotPMD users compared to non-motorised PMD users (NonPMDs) [14‐17], and environmental separation issues (pedestrian vs bicycle lanes vs roads) [18]. MotPMDs also travel at much higher speeds than NonPMD [4, 17, 19]. While there appears to be a higher risk of injury for MotPMD users [5], there are very few studies evaluating the relationship between PMD type (MotPMD vs NonPMD) and the severity of injury. Existing studies have so far only evaluated e-bikes in relation to conventional bicycles, but other MotPMD types such as e-scooters are becoming more popular [12, 13].

In Singapore, trauma is the leading cause for hospitalisation, and one of the major causes of mortality [20]. The Singapore National Trauma Registry (NTR) was established in 2011, covering all public hospitals in Singapore. Using NTR information, our primary goal was to identify and evaluate risk factors for higher injury severity (Injury Severity Score, ISS > =9) [21, 22], and for inpatient hospital admission in PMD users.

To our knowledge, our study is the first to examine factors associated with injury severity and hospitalization in personal mobility device riders across a range of PMD types, using data that is nationally representative in an urban city state. Other studies have focused on specific types of PMDs. We found that MotPMD users had higher injury severity scores, with a greater proportion requiring surgical intervention compared to NonPMD users, as has been reported by other authors [5, 18]. Our study, however, is one of the few that included a NonPMD comparator group, suggesting that MotPMD users are at higher risk of injury compared to NonPMD users.

MotPMD use and older age were identified as factors independently associated with severe injury. A similar pattern was found in the subgroup analysis of e-scooters, although this only reached statistical significance for severe injury, possibly due to smaller subgroup sample size. This is in keeping with the findings from studies conducted in China and Switzerland [3, 13], focusing on pedal cycles versus electric-bicycle users, which also found higher injury severity for electric-bicycle users.

Older age was associated with higher risk of significant injury or admission, likely due to higher fall risk and frailty. Studies of motor vehicle crashes have also shown that the older patients tend to sustain higher injury severity and mortality [25‐29]. In common with motor vehicle crash-injured patients, older PMD riders are likely to have reduced physiological reserves and impaired response to injury [30‐32], coupled with comorbid conditions that predispose to injury or further reduce resilience [32, 33], and propensity for fracture even with minor trauma [34]. In addition, older riders are probably choosing to ride MotPMDs to overcome their pre-existing musculoskeletal problems, and these patients may be more frail than younger patients to begin with.

While our study did not specifically examine PMD rider behaviour, we did find that the majority of the MotPMD users did not use protective helmets, in line with the risk-taking profile found in other studies [3, 13‐17, 28].

MotPMD-related reasons such as higher travelling speeds [4, 17, 19], and environmental issues such as lack of dedicated lanes vs usage of mixed-use conventional bicycle lanes, sidewalks or roads have also been proposed as contributory factors to injury [18]. MotPMD-related legislation varies between countries. In the European Union, MotPMDs are barred from motor vehicle roads, and are allowed only on sidewalks at speeds < 6 km/hr. [35]. In the United States, there is great variability between the states, with some permitting road usage [35]. In Singapore, new legislation (Active Mobility Act) now restricts use to only sidewalks or shared bicycle lanes, but at maximum speed of 25 km/hr. Our study was conducted prior to the implementation of the new regulations. Future studies focusing on interventional strategies for injury prevention would be of great policy interest, such as examining the differences in incidence and economic burden of PMD-related injury before and after legislative rules controlling MotPMD use, especially given the significant association of MotPMDs with severe injury and admissions.

The main strength of our study was that it covered all the public-sector institutions nation-wide in an urban multi-ethnic population. However, the use of NTR data had some limitations. Certain information such as PMD type and helmet use was incomplete. Nevertheless, data quality was good for injury severity and need for hospital admission, data that is routinely collected by the NTR. Another limitation is that the NTR only captures data for patients who present to the emergency department of public hospitals, and hence our study findings may not apply to riders who self-medicate or see their family physician.

MotPMD riders had triple the risk of severe injury and double the risk of requiring hospitalisation compared to NonPMDs. Increased age was also associated with severe injury and requiring hospitalisation.