Date of Award

January 2020

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)



First Advisor

Jason Gerrard


Shared micromobility programs (SMPs) provide access to a distributed set of shared vehicles – mostly conventional bicycles, electronic bicycles, and electronic scooters – and are increasingly common in domestic and global cities, with riders completing an estimated 84 million trips using an SMP vehicle. There is heterogeneity in these programs in size, vehicle types offered, and distribution model. The impact of SMP introduction on the epidemiology of traumatic injury is largely unknown, and the relative safety of different shared vehicle types has not been evaluated; these effects are the subject of this study.

Considered as a whole, the annual number of traffic-related bicycle deaths in the United States has been increasing in the last decade. The 30 most populous cities in 2010 were selected for closer analysis. For each year in each city from 2010 to 2018, the crude rate of traffic-related bicycle deaths per-person and per-trip was calculated, and the year in which any SMP was introduced was identified. Interrupted time-series analysis demonstrated that SMP introduction was not associated with changes to these rates but was associated with an increase in estimated number of bicycle trips.

National data suggest that rider demographics, and therefore population at risk, may shift with the availability of new vehicle types and SMPs. Injured e-scooter riders, in particular, have near parity in the gender of injured riders, a stark contrast to the nearly 3 to 1 ratio of males in bicycle trauma, and SMP riders are disproportionately young adults. The importance of these shifts was highlighted in analysis of the 2017 National Trauma Database®, which yielded 18,604 adult patients. This analysis showed that older age, male gender, accident involving a motor vehicle, and failing to use a helmet were associated with more severe injuries and mortality. It also demonstrated that the risk reduction afforded by helmets to females was less than the same for males in multivariate analysis. These findings contextualize a review of studies of trauma involving motorized micromobility vehicles.

Finally, to explore mechanisms of differential injury by vehicle type, structured observations of riders of personal and shared vehicles were performed in San Francisco over 2 months in the spring of 2019. In total, 4,472 riders were observed, approximately a fifth of whom used a shared vehicle. Riders of shared vehicles were more likely to use a motorized vehicle including e-scooters and e-bicycles, but helmet use was lower among this cohort (37.3%), compared with riders of personal vehicles (84.6%). Use of a shared vehicle, an e-scooter, and a dockless shared vehicle were associated with decreased likelihood of helmet use. Nonetheless, shared vehicle riders were equally likely to observe traffic regulations. Riders of e-scooters were more likely to stop correctly at intersections but also more likely to ride on the sidewalk than riders of conventional bicycles (c-bicycles) and electronic bicycles (e-bicycles).

Given the popularity of SMPs and their success in augmenting urban public transport systems, some form of SMP will likely remain a fixture in urban environments for the foreseeable future. The data collected here provide motivation for and guidance in developing safer SMPs and can potentially be used as agents of public health to tailor SMP characteristics to support safe practices and protect vulnerable road users.


This is an Open Access Thesis.

Open Access

This Article is Open Access