# The Effect of Speed Humps on Instantaneous Traffic Emissions
## 5 Conclusions  
We presented results on the negative effect of speed humps on instantaneous traffic emissions on a single lane. We used a modified version of the NaSch model and an instantaneous traffic emissions model to study the effect of speed humps on traffic emissions. The microscopic approach followed in our study allow us to characterize the effect of a large number of speed humps on roads, and neglect external effects (traffic lights, pedestrian crossings and intersections). Our results take into account decelerations of vehicles due to the presence of speed humps. This would be extremely difficult to perform on real traffic scenarios. On the one hand due to the large number of external factors that may introduce variations on measurements such as driver's behavior, number of monitored vehicles, large variability on vehicles types, weather conditions and road conditions. On the other hand, the limitations on the specialized measurement equipment would introduce constraints on the distance between speed humps, type and number of monitored vehicles. Besides, the reported absolute emission values should be considered to be peak values since the models used in our study do not consider weather effects such as wind that may reduce the concentration of pollutants at a given area. The main findings of this work are that for \(P=0.1\) and density of vehicles in the range \(0<\rho\leq 0.48\) there is a strong to middle influence of speed humps on the generation of CO\({}_{2}\), NO\({}_{x}\) and PM emissions. The peak on emissions for CO\({}_{2}\), NO\({}_{x}\) and PM is reached at the transition phase (\(0.12<\rho\leq 0.48\), between free flow and the congestion phase), where the average speed of vehicles is  
Figure 14: PM instant emissions as a function of the number of speed humps. about 20 km/h. Additionally, we found that a road with a low density of vehicles and just a few speed humps may generate more pollutants than a highly occupied road. Regarding VOC emissions, the experiments shown very low influence of speed humps either for low or high densities. Other findings are summarized as follows:  
* There are at least three phases for traffic flow and pollutants emissions as a function of density, these phases are in the range: \(0<\rho\leq 0.12\) for the first phase, \(0.12<\rho\leq 0.48\) for the second phase, and \(0.48<\rho\leq 1\) for the third phase. * For low density of vehicles, the rise on CO\({}_{2}\), NO\({}_{x}\) and PM emissions as we increase the number of speed humps on a lane provides evidence of the influence of speed humps on traffic emissions. We also found that slight variations on the position and distance between speed humps influence the generation of pollutants at low densities. * For high density of vehicles, the impact of speed humps on average velocity and traffic flow may be ignored because most of the vehicles are not moving due to traffic jams. Our findings reveal that for roads with a low number of vehicles, speed humps highly increase CO\({}_{2}\), NO\({}_{x}\) and PM emissions. Moreover, their overuse has a dramatic impact on the generation of those pollutants. Urban planners and traffic managers can use our results to evaluate the feasibility of speed humps deployment (quantity) since the determined pollution effect has considered both velocity bounds and fluctuations, involved in acceleration and deceleration dynamics. Ongoing research is focused on the effect of multiple vehicles types on instantaneous traffic emissions. Further studies will consider the generation of pollutants as a function of the position and distance between speed humps. We will also consider the effect of driver's behavior and different speed regulation strategies such as traffic lights, pedestrian crossings and speed limit areas on the generation of free pollutants. Conceptualization, J.C.P.-S., N.L., J.G.-D. and S.E.P.H. ; Investigation, J.C.P.-S., N.L., J.G.-D. and S.E.P.H. ; Methodology, J.C.P.-S. and N.L. ; Software, J.C.P.-S. and N.L. ; Validation, J.C.P.-S. and N.L.