# A Comparative Study of the Availability of Electric Buses in the Public Transport System
## 4 Discussion of Results  
The results of the study indicate that electric buses have higher availability compared to diesel buses. The differences were shown to be statistically significant. The average technical availability in the sample of electric buses is in the range K\({}_{\text{G,avg}}\) (\(0.76\div 0.92\)) while that of diesel buses is in the range K\({}_{\text{G,avg}}\) (\(0.74\div 0.85\)). These results are in line with reports from the literature. Indeed, many authors emphasised the systematic improvement in the quality of electric drives introduced to the market in recent years [31; 32; 33]. In comparison with the availability of Solaris diesel buses operated in Municipal Transport Company in Lublin in the 2008-2010 period, whose availability was K\({}_{\text{G}}\) = (0.88-0.91) [13], it may be considered that the results of the availability assessment of electric buses presented in this study do not differ significantly. The time series of the K\({}_{\text{G}}\) indicator of electric vehicles in the three initial years of operation is characterised by the lack of a trend. On this basis, it is possible to forecast the maintenance of a stable availability in the subsequent periods of bus operation. In addition, a seasonality of changes in the technical availability index after the first year of operation was found. The moving average in Figure 3 shows a decrease in the indicator in a repeated cycle of about 6 months. This is probably related to the 6-month cycle of periodic inspections of electric vehicles. Electric vehicles were introduced to operation in a similar period of time (within 1 month). That caused periodic inspections of all vehicles to fall at the same time. Even if vehicles were serviced simultaneously in smaller groups in the span of one month, the overall technical availability would be lower in this month. The reasons for the differences in availability between electric and diesel vehicles can be of a technical nature related to the reliability of the design or of an operational nature related to managing the continuity of the fleet. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Operating** & **Variable** & **Effect** & **Source** & **\begin{tabular}{c} **Sum of** \\ **Squares** \\ \end{tabular} & **Degrees of** & **Mean** & **F** & **Significance** \\ \hline \multirow{4}{*}{1 st year} & & & Between & 0.012 & 1 & 0.012 & 3.814 & 0.065 \\  & & & \
\begin{tabular}{c} Inside \\ phases \\ \end{tabular} & 0.064 & 20 & 0.003 & & & \\  & & & Total & 0.077 & 21 & & & \\ \hline \multirow{4}{*}{2 nd year} & \multirow{4}{*}{K\({}_{\text{G}}\)(t)} & & Between & 0.187 & 1 & 0.187 & 56.346 & \textless{}0.001 \\  & & &
\begin{tabular}{c} Inside \\ phases \\ \end{tabular} & 0.073 & 22 & 0.003 & & & \\  & & & Total & 0.260 & 23 & & \\ \hline \multirow{4}{*}{3 rd year} & & & Between & 0.066 & 1 & 0.066 & 29.796 & \textless{}0.001 \\  & & & Inside & 0.035 & 16 & 0.002 & & \\  & & & Total & 0.101 & 17 & & \\ \hline \hline \end{tabular}  
* Mean square between groups divided by mean square within groups.  
\end{table} 
Table 6: _Cont._ \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test** & **Statistics** & \begin{tabular}{c} **Degrees of** \\ **Freedom df1** \\ \end{tabular} & \
\begin{tabular}{c} **Degrees of** \\ **Freedom df2** \\ \end{tabular} &
\begin{tabular}{c} **Significance** \\ \(p\) \\ \end{tabular} \\ \hline Welch & 3.814 & 1 & 16.877 & 0.068 \\ Brown–Forsythe & 3.814 & 1 & 16.877 & 0.068 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Results of Welch and Brown–Forsythe tests for 1 st year of operation. One of the key factors for the high technical availability of electric buses is their technical quality. It can be assumed that electric buses have been made to a higher standard of quality than their diesel counterparts. The reason for this may be the growing construction and technological experience of the vehicle manufacturer (Solaris Bus & Coach SA, Owinska, Poland) and high production standards.