# Experimental Light Rail Traffic Noise Assessment in a Metropolitan Area
## 3 Effects of Different Parameters on Sound Pressure Level
### Analysis of the Influence of Traffic Speed on Different Types of Tracks  
In this section, we analyze the influence of speed on sound pressure levels. As explained in Figure 1, increasing traffic speed implies an increase in sound pressure levels. The first step was to analyze the Type II track where the vehicle _Flexity Swift_ is operating. In this case, speeds vary from 64 km/h to the maximum speed recorded on the line, 82 km/h. As already mentioned, in Figure 9, we observe an increase in the sound pressure levels as the circulation speed increases. It is important to note that there is no significant change in the frequency content of the measured levels, and thus, despite the change in sound pressure levels, the maximum levels for each record are registered for the same frequency bands. Taking into account the different sound pressure levels it is expected that the values of the indicator \(L_{Aeq,T}\) will increase according to the velocity increase. Thus, for the vehicle circulating at 64 km/h and for the most distant receiver, a value of 85 dBA was obtained. For the vehicle circulating at 75 km/h, the value of \(L_{Aeq,T}\) is 93 dBA and, finally, for the vehicle with the highest velocity, the indicator value is 93 dBA.  
The same type of analysis can be carried out for the _Eurotram_ type vehicle. In this case, the speed varies between 40 km/h and 60 km/h. The results presented in Figure 10 show that, as concluded in the case of the _Flexity Swift_, the sound pressure levels increase as the speed increases, but the most prominent frequency content remains the same in the identified records. For the case under analysis, it is also expected that the value of \(L_{Aeq,T}\) is increasing with the velocity of circulation, however, with lower values than those analyzed, given the lower levels of sound pressure. Thus, for the vehicle circulating at 40 km/h, a value of 83 dBA was obtained, and for the other two cases, values of 86 dBA and 88 dBA for vehicles circulating at 50 km/h and 60 km/h were obtained, respectively.  
Figure 8: _Flexity Swift_ and _Eurotram_ vehicles traveling at 40 km/h on a Type III track: (**a**) Microphone 1; (**b**) Microphone 2.  
Figure 9: Comparison between different speeds for the _Flexity Swift_ vehicle operating on a Type II track: (**a**) Microphone 1; (**b**) Microphone 2.  
Finally, the influence of speed is evaluated for the Type I track. The records presented in Figure 11 relate to the passage of a vehicle _Eurotram_. A slight increase in the sound pressure levels is observed with the increase in the speed of circulation; however, contrary to what was recorded for the ballasted track, this increase is not significant. There is a very close proximity between the sound pressure levels for speeds of 39 km/h and 50 km/h In this case, given the proximity of the two spectra analyzed, it is expected that the values of \(L_{Aeq,T}\) are also very close. Thus, a value of 76 dBA was obtained for the vehicle circulating at 39 km/h and a value of 77 dBA for the vehicle circulating at 50 km/h. The considerable difference (about 7 dBA) of this indicator concerning the previous case should be noted; it is strongly influenced by the type of track on which the records were made.