## 4 Discussion
### RQ2: What Thermal Comfort Parameters Were Investigated in the Studies That Analyzed Bus Cabins? Table 8 presents the thermal comfort parameters investigated by the studies included in this review. Observing Table 8, it is possible to note that the parameters air temperature and air velocity were widely employed in the analyses of thermal comfort in bus cabin environments. This occurrence is explained by the control of air-conditioning systems, which in general control the temperature and velocity of air to cool or heat the environment. Moreover, of the 22 papers included in this review, eight [5; 9; 15; 16; 31; 48; 53; 54] analyzed the six parameters that are widely employed in the standard models of thermal comfort by ISO or ASHRAE [37; 40]. It is worth pointing out that the table above only presents the parameters of this knowledge area, but these studies employ other variables, related to other types of comfort and the sociodemographic characteristics of the occupants. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Approach** & **References** & **Total** & **\%** \\ \hline Thermal sensation & [5; 9; 10; 11; 13; 14; 18; 31; 46; 47; 48; 53; 55] & 16 & 73\% \\ Productivity & [19; 51] & 2 & 9\% \\ Energy or fuel saving & [15; 16; 17; 54] & 4 & 18\% \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Approaches adopted in the objectives of the studies included by this review. In the studies of [PERSON] et al. [19; 51], the environmental and personal parameters were not measured but rather presented as questions to the drivers and correlated with the driving activity through questionnaires. In the studies by [PERSON] et al. [14], [PERSON] [15] and [PERSON] et al. [53], besides the measurable parameters listed in Table 8, the occupants were asked regarding subjective votes, such as the thermal sensation vote, the thermal preference vote, and the thermal acceptability vote, through questionnaires. Overall, knowing these votes in thermal comfort studies is relevant due to two reasons: first, to know the operating adaptive methods of the users in adapting themselves to uncomfortable situations; second, to assess the predictive models through the discrepancies between analytical values and real subjective values. In bus cabin environments, these votes served to understand the occupants' adaptive behavior in choice of preferred seats, opening and inclination angle of the air outlets of the ventilation and air-conditioning systems, opening or closure of curtains due to solar radiation, and choice of clothing [14; 15; 53]. RQ\({}_{3}\): Besides Thermal Comfort Parameters, What Other Variables Were Analyzed by Thermal Comfort Studies Conducted in Bus Cabins? Table 9 exposes the types of comfort investigated along with thermal comfort in the studies conducted in bus cabins. Table 9 shows that of the 22 research papers included in this review, 12 intended to assess only thermal comfort [9; 15; 16; 18; 19; 31; 47; 50; 51; 53; 55; 56]. Moreover, in bus cabins, the comfort knowledge area \"air quality\" was the most investigated along with the thermal area, followed by the acoustic, acceleration, and lighting comfort types. Air quality comfort, investigated in bus cabin environments, is usually linked to the concentration of pollutants and suspended particles that might be inhaled through breathing by the occupants of the environment. The concentrations of carbon monoxide and dioxide (CO and CO\({}_{2}\)) are among the most examined pollutants [17; 47; 48]. However, the concentrations of ozone (O3) [11] and sulfur dioxide