# The Effect of Speed Humps on Instantaneous Traffic Emissions
## 4 Results and Discussion
### The Impact of Speed Humps on \(\mathrm{CO_{2}}\) Emissions
#### 4.2.4 The Impact of Speed Humps on PM Emissions  
Finally, in Figures 13 and 14 we present the results for PM emissions. Figure 13 shows PM emissions as a function of density for different number of speed humps. The reported ranges go from 0.01 to 1.0 for \(\rho\), and from 0 g/s to 0.0027 g/s for PM emissions. The maximum emission values are in the range from 0.0024 g/s to 0.0026 g/s. We observe three phases, the first one for \(0<\rho\leq 0.12\) which shows large differences on the initial PM emission values for each of the test cases. This suggest that at this phase speed humps highly influence the generation of PM emissions due to deceleration and acceleration of vehicles when encountering them. The second phase \(0.12<\rho\leq 0.48\) shows an increase on PM emissions for all the cases, for the cases with 1, 3, 5 and 10 speed humps the increment on PM emissions is very rapid while for the cases with 20 and 30 speed humps the increment is moderate. These variations result from the changes on velocities of vehicles due to speed humps and the interaction with other vehicles. Notice that all the studied cases reach their highest PM emissions in this phase. The third phase for \(0.48<\rho\leq 1\) shows a sudden fall and an overlap of the curves representing PM emissions, this overlap is mostly due to local congestions. For large densities speed humps have no major effect on the generation of PM emissions. Observe that all cases converge to the \(f_{1}\) value from Table 2 as we increase the density.  
We also performed simulations with more than 30 speed humps to study the effect of a large number of speed humps on PM emissions. In Figure 14 we show PM emissions as a function of the number of speed humps for different density values. For \(\rho=0.1\) we have an upward trend on PM emissions as we increase the number of speed humps on the lane. As in the previous cases, the behavior of the curve is due to the standard deviations observed for velocity, see Table 1. The case with \(\rho=0.3\) presents a slight increase on PM emissions for a larger number of speed humps, \(\rho=0.3\) represents the transition phase where the emissions depend on the acceleration and deceleration of  
Figure 13: PM instant emissions as a function of density.  
vehicles from the interaction with speed humps and with other vehicles on the lane. The case with \(\rho=0.8\) shows no variations on PM emission values as the number of speed humps grows.  
In Figure 14, note that the curve with \(\rho=0.1\) cross the other curves at a low and a moderate number of speed humps. This suggests that roads with low density of vehicles and a reduced number of speed humps produces the lowest PM emissions. Conversely, as we increase the number of speed humps, a road with low number of vehicles generates more PM emissions than a highly occupied road (\(\rho=0.8\)). Additionally, with more than 40 speed humps, the road with low density of vehicles generates more PM emissions than a road with medium density (\(\rho=0.3\)).  
The previous results suggest that speed humps influence the generation of PM emissions for low density of vehicles but have no considerable impact for large densities. Moreover, a road with very low density but with a large number of speed humps produces more PM emissions than roads with higher densities.