## 7 Results of Simulation Studies  
Based on the expressions presented in the above sections, a simulation model was prepared to schedule the progress of mining works in the room and pillar systems. In this model, the selection of means of transport was based on the method proposed in Section 6, taking into account environmental aspects. The calculated HC+NOx pollutant emission level for the transport of the winning with tire haulage was used as one of the criteria for evaluating the solution (Formula (13)) as a function of the objective (Formula (14)). For the first simulation tests, the implementation of transport with vehicles meeting the Stage II emission standard was assumed. For the calculations, the pairs of weights in the range \(w_{1}=0\) and \(w_{2}=1\) (the situation in which the cost of transport is negligible, the result in 100% is determined by the minimum level HC+NOx) up to \(w_{1}=1\) and \(w_{2}=0\) (the situation in which the result in 100% depends on the cost of transport, while HC+NOx emissions are not taken into account) were adopted. The calculation results are presented in Figure 10.  
It is not surprising that the highest level of HC+NOx emission was recorded with the minimum cost of the winning transport during the exploitation of the mining field. It is interesting, however, that it is possible to significantly reduce the level of HC+NOx emissions (from 35,110 to 18,860 kg over more than 3 years of operation) by the skiful selection of the type of means of transport, even if all loaders and haul trucks meet the same Stage II standard. The potential of a possible reduction of HC+NOx emissions is better illustrated by the presentation of percentage values--Figure 11.  
Figure 10: Dependence of the HC+NOx emission level on the transport costs of the winning, depending on the adopted weights of optimization criteria as a function of the objective. The obtained dependence shows that a 20% reduction of HC+NOx emission is possible using the proposed method of selecting the means of transport, with a 2% increase in the cost of the winning transport. The nature of the dependence is similar to the well-known Pareto principle, although an 80% reduction of emissions turned out to be impossible to achieve, regardless of the costs of transporting the output. Further simulation tests were carried out with the assumption that the deep mine replaces the means of transport for those complying with Stage IIIA, Stage IIIB and Stage IV emission standards. Analogous simulation tests on the method of selecting the types of transport means according to the objective function (expression 14) were carried out, as presented for Stage II standards. The results of the calculations are presented in Figure 12 to facilitate comparison. Figure 11: The potential to reduce HC+NOx emissions from the transport costs of the winning, depending on the adopted weights of optimization criteria as a function of the objective. Figure 12: The level of HC+NOx emissions during transport of the winning depending on the standards met by loaders and haulage vehicles; In each case, the proposed method of selecting means of transport was used. The proposed method has proven successful in the case of using loaders and haulage trucks meeting Stage IIIA, Stage IIIB and Stage IV emission standards for the transport of the winning. The calculations show a reduction in HC+NO\({}_{\text{x}}\) emissions during the transport of the winning from 35,110 kg for the Stage II standard to 1077 kg for the Stage IV standard. This is a very large reduction that confirms how restrictive the current standards are, while the permissible level of HC+NO\({}_{\text{x}}\) emission for the combustion engines in the power range from 56 to 560 kW is the same for Stage IV and Stage V.  
The driving style of the loader and hauler operators also has an impact on exhaust emissions. Unfortunately, we did not have portable emissions measurement systems (PEMS), nor did we have permission from the mine management to make such measurements.