# Impact of Environmental Factors on Passenger Ride Comfort
## 7 Results of Experimental Studies
### Ride Comfort Index
A similar outcome is found for the car on the main road and the new metro train, where the overall comfort level described by the primary index \(\mathrm{C}\) is also identical in both cases. Notably, these journeys cannot be further differentiated using the secondary index \(N_{C}\) or the expanded index \(C_{exp}\). However, it has to be emphasised that this result is specific to the examined journeys and does not imply any deficiency in the present method. In general, journeys with the same primary index \(C\) can be further discriminated with respect to the overall comfort level by employing either the index \(N_{C}\) or, if necessary, the expanded index \(C_{exp}\). The results obtained show that, despite differences in travel environment characteristics and vehicle parameters, the method of the synthetic comfort index enables the direct comparison of different modes of transport. The proposed method of using the minimum function for calculating the overall comfort index ensures that no individual factor is undervalued in the assessment and effectively identifies the factor with the lowest comfort rating. Primarily designed for comparing ride comfort across different journeys and modes of transport, this method also provides a structured approach to pinpointing the specific environmental comfort factors that most affect passengers. By identifying these critical areas, it offers actionable insights for improving the overall travel experience across different modes of transport. In particular, the findings of the present study emphasise that noise levels play a pivotal role in determining the overall comfort rating. Excessive noise was identified as a significant contributing factor to the reduced sensation of comfort in both the old metro train and the passenger car on the road with poor pavement quality. This highlights the need for targeted interventions, such as enhancing pavement quality, improving train body insulation, and implementing advanced noise-damping technologies or even replacing the rolling stock with newer ones. The methods used to evaluate overall ride comfort and the resulting outcomes differ significantly compared to the Montreal study [30]. In the present work, the overall comfort level is determined by the lowest rating among individual comfort indices (C1-C4), with a uniform five-point scale used for all aspects of comfort: vibrational, acoustic, thermal, and visual. In contrast, the Montreal metro study employs varied scales for different comfort factors and includes additional aspects, such as air quality, which were not considered in this study. Furthermore, in that study, the synthetic index of overall comfort is defined as the geometric mean of the partial comfort indices, which differs very substantially from the present definition of this index. These differences highlight the complexity of cross-study comparisons and emphasise the need for standardised approaches to ride comfort evaluation. Nevertheless, the overall comfort index, with the respective values of 0.65 and 0.84 (on the [0, 1] scale) obtained for the old and new metro cars in the Montreal study, corresponding to the \"fair\" and \"comfortable\" grades in the qualitative scale used in that study, agree well with the corresponding levels of comfort, C = 3 and C = 4, presently determined for old and new trains in the Warsaw metro. The present results also show that acoustic comfort was the decisive factor in lowering the overall comfort rating for metro trains, resulting from high noise levels in older trainsets. Similarly, in Montreal's metro, acoustic comfort was a significant concern, with only marginal improvements observed in newer cars. For thermal comfort, both studies identify relevant environmental factors as critical determinants: the Montreal study reports discomfort during winter due to overheating, while in the current analysis, differences between old and new metro trainsets suggest the impact of advancements in HVAC systems.