# The Effect of Speed Humps on Instantaneous Traffic Emissions
## 4 Results and Discussion
### The Impact of Speed Humps on \(\mathrm{CO_{2}}\) Emissions
#### 4.2.3 The Impact of Speed Humps on VOC Emissions  
In Figures 11 and 12 we show the results on the impact of speed humps on VOC emissions. Figure 11 shows VOC emissions as a function of density for different number of speed humps. We observe three phases as in the previous cases. Note that the ranges go from 0.01 to 1.0 for \(\rho\), and from 0.0040 g/s to 0.0045 g/s for VOC. The maximum values are reported at the maximum density value; \(\rho=1\). In the first phase with \(0<\rho\leq 0.12\) there is a clear but very low difference in the initial VOC values for all the test cases. The difference is in the order of 1.5e-4 which indicates a very low effect of speed humps on VOC emissions in this phase. The second phase with \(0.12<\rho\leq 0.48\) shows a downward trend on VOC emissions as we increase the number of speed humps. All the test cases show a rapid fall on VOC emissions; reaching its minimum in the interval 0.0040 g/s and 0.0041 g/s. The third phase for \(0.48<\rho\leq 1\) shows a sudden rise and an overlap for the curves representing the VOC emission for \(\rho>0.8\), this suggests that the rise on VOC emissions is due to the increase on density and not from the increase on the number of speed humps. Observe again the convergence to the \(f_{1}\) value from Table 2 for all the cases.  
Figure 10: NO\({}_{x}\) instant emissions as a function of the number of speed humps.  
To study the effect of a large number of speed humps on VOC emissions we performed simulations with up to 100 speed humps installed on a lane. In Figure 12 we show VOC emissions as a function of the number of speed humps on a lane for different densities. Consider the case \(\rho=0.1\) representing the first phase, observe the decrease on VOC emissions as the number of speed humps on the lane grows. The difference between the initial and the final values suggest a low influence of speed humps on VOC emissions. Representing the second phase we have \(\rho=0.3\) with a very low decrease on VOC emissions as we rise the number of speed humps. Finally, the case \(\rho=0.8\), representing the third phase shows no difference from the initial to the final VOC emission values as the number of speed humps increases.  
From Figure 12 observe that the curve \(\rho=0.1\) cross the other two curves, therefore:  
* for a moderate number of speed humps, a road with a low number of vehicles generates more VOC emissions than a highly occupied road (\(\rho=0.8\)),
* for a larger number of speed humps, a road with a high number of vehicles generates more VOC emissions than a low to middle density roads (\(\rho=[0.1,0.3]\)),  
Figure 11: VOC instant emissions as a function of density.  
Figure 12: VOC instant emissions as a function of the number of speed humps.  
* for a large number of speed humps, a road with a low number of vehicles (\(\rho=0.1\)) produces a similar quantity of VOC emissions than a road with a moderate number of vehicles (\(\rho=0.3\)).  
The previous analysis suggests that in general, speed humps have very low effect on VOC emissions since the variations are in the order of 0.0005 g/s. However, when looking for the configurations with lower VOC emissions we found that a high number of speed humps minimally reduces VOC emissions for roads with very low density.