## 4 Methods  
Economic aspects play a very important role in the case of shared mobility services. This role is all the greater when it comes to replacing classic vehicles with autonomous vehicles; however, in order to know exactly how the economy influences car-sharing, based on our own research, a survey was conducted to identify the economic aspects of car-sharing and autonomous car-sharing systems. We constructed a questionnaire in which the public could express their opinion on the costs of car-sharing and the costs of autonomous vehicles. The respondents' task was to determine the most critical factors affecting the economic aspects of travel via various types of vehicles, including autonomous vehicles in urban transport systems. The study was addressed to people using car-sharing services and was made available via the Internet by various groups of people associated with car-sharing users. The survey was conducted among German users in January 2020. The survey received 208 responses. The research sample was representative. The population contains 82 million people, and a fraction size of 0.5 resulted in a maximum error of 7%. The confidence level was \(\alpha\) = 0.95. The respondents' responses were analysed and classified into the 16 main most recurring factors. The list of factors is presented in Table 1.  
The most important factors from the point of view of the respondents are presented in Figure 4.  
In order to analyse the selection of the right vehicle type for journeys in urban, intelligent transport systems due to economic factors, we proposed a research experiment. In the first step, we conducted heuristic research (Delphi method). The Delphi method is a structured communication technique or method, originally developed as a systematic, interactive forecasting method, which relies on a panel of experts [27; 28; 29; 30]. Scientists around the world widely use the Delphi method because of its many strengths. The most important advantages of the method are the following [31; 32]:  
* Independence of expert opinions;
* The anonymity of spoken courts;
* Multistage proceedings;
* Finding agreement and summing up the opinions of competent persons;
* No dominants imposing their opinions on other people in the group; \begin{table}
\begin{tabular}{c c} \hline \hline
**No.** & **Factor** \\ \hline
1 & Vehicle type \\
2 & Vehicle maintenance cost \\
3 & Travel distance \\
4 & Travel time \\
5 & Cost of non-public car parks \\
6 & Cost of public parking \\
7 & Cost of the car-sharing service package \\
8 & Cost for keeping the vehicle for yourself for a specified time \\
9 & Costs of violations of the car-sharingperator regulations \\
10 & Vehicle purchase cost \\
11 & Vehicle rental cost \\
12 & Cost of violations (e.g., improper use, parking)—fines \\
13 & Vehicle class \\
14 & Financial bonuses for using car-sharing (e.g., 5 min for free ) \\
15 & The amount of additional fees (e.g., departure outside the zone) \\
16 & The existing car-sharing system in the city \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of the most recurring critical factors affecting the economic aspects of travel via various types of vehicles, including autonomous vehicles in urban transport systems—study results. * No reluctance to express one's opinion;
* Results obtained based on the opinions of specialists. In turn, the most frequently mentioned weaknesses include the following [31,32]:  
The need to involve a large number of people;  
* A time-consuming process;
* No direct exchange of views between experts;
* Difficulties in choosing the right people;
* Little involvement of experts if they are not familiar with the problem. This method was used to obtain information from experts in the field of intelligent transport systems. The number of specialists who took part in the study was determined based on Equation (1) [33]:  
\[S_{min}=0.5*\left(\frac{3}{\alpha}+5\right)=32.5\ \sim\ 33 \tag{1}\]  
where:  
\(S_{min}\)--minimum number of experts;  
\(\alpha\)--statistical significance, \(\alpha=5\%\).