## 2 Theoretical Framework
### Where Shared e-Scooters Are Used and by Whom  
The usage of shared e-scooters in cities has been influenced by temporal, socioeconomic, and built-environment variables. This work focuses on socioeconomic variables for the usage of this service in order to evaluate the potential of shared e-scooters to reach a diverse group of people, in other words, how equitable the usage of shared e-scooters is in cities.  
Therefore, some researchers have indicated that shared e-scooters are more used in areas with more employment rates between residents, and where the presence of bicycle infrastructure is higher [48]. Moreover, mixed-use regions have the smallest portion of non-recreational trips, while downtown areas have the highest usage of shared e-scooters for non-recreational trips, along with institutional-oriented mixed-type regions [49].  
Moreover, the presence of commercial regions, along with encouraging environments for active transport (i.e., walking and cycling), as well as the proximity to public transport stations and hubs, were also correlated with high usage of shared e-scooters, which can suggest that this mode of transport is associated positively with sustainable development [50; 51].  
In addition, the presence of shared e-scooters near and on university campuses, combined with the ability to appreciate the ease of use of this \"new\" mode of transport, and the availability of smartphones and online payments, make university students a strong group of shared e-scooter services around the world [52].  
Students and other specific groups of users have been reported to be a constant in shared e-scooter usage even if this service is located in different cities and urban contexts. In Paris, for example, shared e-scooter users are usually 18-to-29-year-old males who have a high educational level; they can be either students or executives who are significantly wealthier than the general French population [51; 53; 54]. Similar results were obtained in Vienna, Austria, where the majority of e-scooter users are young to middle-aged and highly educated men [55]. Table 1 presents the socioeconomic characteristics of users among cities in Europe and America in order to draw a profile of the public covered by shared e-scooters services.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Location**} & \multicolumn{5}{c}{**Profile**} \\ \cline{2-6}  & **Gender** & **Age** & **Educational Level** & **Occupation** & **Income Level** \\ \hline Paris, France & Male & 18–25 years old & High & Students/executives & High income \\ \hline Vienna, Austria & Male & 26–35 years old & High & Students/employed & - \\ \hline Thessaloniki, Greece & Male & 18–27 years old & - & - & Medium income \\ \hline Zurich, Switzerland & Female & 21–30 years old & High & Employed & High income \\ \hline Trondheim, Norway & Male & 18–35 years old & - & - & - \\ \hline Gdansk/Gdynia/Sopot, Poland & Male & 31 years old & - & Student/employed & Medium income \\ \hline Great Golden & & 25–40 years old & High & - & - \\ \hline Chicago, USA & Male & 25–34 years old & High & - & High income \\ \hline Austin, USA & Male & - & High & - & Low income \\ \hline \hline \end{tabular}
\end{table}
Table 1: Socioeconomic profile of shared e-scooter users.  
Table 1 shows that users of shared e-scooters are usually young men who have high educational levels and medium-to-high-income levels; only in Zurich are women the most predominant gender amongst users. This illustrates the possible gender, age, and income disparities promoted in cities when this new mode of transport is introduced. These differences can be also stimulated by the locations where shared e-scooters are deployed in cities. They are usually available in downtown areas, business districts, and near a university campus, which can influence the type of public that is exposed to this mode of transport.