# The Effect of Speed Humps on Instantaneous Traffic Emissions
## 4 Results and Discussion
### The Impact of Speed Humps on \(\mathrm{CO_{2}}\) Emissions
#### 4.2.2 The Impact of Speed Humps on NO\({}_{x}\) Emissions  
In Figures 9 and 10 we present the results on NO\({}_{x}\) emissions, in Figure 9 we observe the emissions of NO\({}_{x}\) as a function of density for different number of speed humps. The ranges go from 0.01 to 1.0 for \(\rho\), and from 0 to 0.02 g/s for NO\({}_{x}\). The maximum values reached for this pollutant are in the range from 0.0175 g/s to 0.02 g/s for the studied cases. There are three phases, the first one for \(0<\rho\leq 0.12\) shows a large difference on the initial NO\({}_{x}\) emission values for each test case, this suggests that speed humps have an effect on the generation of NO\({}_{x}\) emissions due to the deceleration and acceleration of vehicles to pass over speed humps. The second phase for \(0.12<\rho\leq 0.48\) shows a rapid increase on NO\({}_{x}\) for the cases with 1, 3, 5 and 10 speed humps, a moderate increase for the 20 speed humps case, and no significant variations on NO\({}_{x}\) emissions for the 30 speed humps case. Please note that all the studied cases reached a peak on NO\({}_{x}\) emissions in this phase. The previous suggest that speed humps promote NO\({}_{x}\) emissions for \(\rho\leq 0.48\). The third phase for \(0.48<\rho\leq 1\) shows a sudden decrease on NO\({}_{x}\) emissions for all test cases due to low speed of vehicles. There is also an overlap for the curves representing the emissions which indicates that speed humps have no major influence on NO\({}_{x}\) emissions for large densities. Please note that all cases converge to the \(f_{1}\) value from Table 2 as we increase the density.  
of NO\({}_{x}\) emissions for low densities. As the CO\({}_{2}\) case, the behavior of the curve is influenced by the standard deviations of the velocity reported in Table 1. For \(\rho=0.3\), most of the acceleration and deceleration of vehicles results from the interactions between vehicles and not from the interaction with speed humps. In this case we note a slight rise of NO\({}_{x}\) emissions as the number of speed humps increases, this suggests a low influence of speed humps on the generation of NO\({}_{x}\). Finally, we have \(\rho=0.8\) from the third phase which shows no variations as we add more speed humps to the lane.  
We also observe that the curve \(\rho=0.1\) cross the curve \(\rho=0.3\) between 28 and 30 speed humps in Figure 10. This suggests that for more than 30 speed humps, a road with low density of vehicles produces more NO\({}_{x}\) than a road with a moderate number of vehicles (\(\rho=0.3\)). Additionally, a low-density road with at least one speed hump generates more NO\({}_{x}\) than a highly occupied road (\(\rho=0.8\)).  
The previous analysis allows us to indicate that speed humps highly influence the generation of NO\({}_{x}\) emissions for low densities. Conversely, there is no major effect of speed humps on NO\({}_{x}\) emissions for higher densities. Moreover, a road with a low number of vehicles and with just a few speed humps produces more NO\({}_{x}\) than highly occupied road.