# The Effect of Speed Humps on Instantaneous Traffic Emissions
## 1 Introduction  
Air quality has become a major topic due to the negative effects of free pollutants on human health. The repeated and chronic exposure to these pollutants may increase the risk of short- and long-term health diseases ranging from the irritation of eyes, headaches and the irritation of the respiratory system, to major health problems such as lung, cardiovascular and asthmatic diseases [1; 2; 3; 4; 5; 6].  
Traffic emissions are identified as one of the primary sources of air pollutants, those with major potential health impacts are carbon dioxide (CO\({}_{2}\)), nitrogen oxides (NO\({}_{x}\)), volatile organic compounds (VOC) and particulate matter (PM) [2; 3; 7; 8]. Actually, traffic emissions account for up to 80% of the total PM emissions [8; 9]. Additionally, the main sources of NO\({}_{x}\) in urban areas are traffic emissions, these NO\({}_{x}\) react with other chemicals to generate ozone (O\({}_{3}\)), both detrimental to human health [2; 10; 11]. Recently, [PERSON] et al. [12] reported that the transportation sector is responsible for 25% of the total energy consumption in the EU, and [PERSON] and [PERSON] [13] identified the main sources of pollution in Campania, Italy. Their findings suggest that in order to limit the generation of pollutants we need to move to new technologies such as biofuel or electric vehicles [14; 15; 16].  
The previously mentioned air pollutants, CO\({}_{2}\), NO\({}_{x}\)), VOC and PM are primarily generated by changing speed and due to the wear of tires by braking [8; 9; 17; 18; 19]. Changing the speed of a vehicle isa common action of every driver during a journey. Drivers accelerate and decelerate to avoid collisions with other vehicles and to stop at traffic lights, pedestrian crossings and traffic-calming measures.  
Speed humps are an effective measure to regulate speed and improve pedestrian safety, they are easy to install and lower on cost when compared with speed cameras, traffic lights, roundabouts and chicanes [20]. They reduce the speed of vehicles by forcing the drivers to decelerate when encountering them, then once passing over them drivers may accelerate if there are no vehicles or obstacles ahead. Although their effect on traffic flow and pedestrian safety has been widely studied [21; 22; 23; 24; 25], there are few studies on their effect on air quality and pollutants generation. Some works monitor pollutants using specialized equipment mounted on cars or installed at control sites [1; 2; 9; 18; 20; 23]. Some others recommend to increase the number of traffic-calming measures and reduce the distance between them to improve safety on pedestrians [22; 25]. However, these recommendations may have negative side effects as we will show. In this work we investigate the impact of speed humps on traffic emissions, we present our findings on the effect of an increasing number of speed humps on traffic flow and its impact on pollutants generation, specifically, CO\({}_{2}\), NO\({}_{x}\), VOC and PM emissions.  
The rest of the document is organized as follows: in Section 2 we present previous studies on traffic-calming measures and pollutants emissions, then in Section 3 the models for traffic flow and instantaneous traffic emission used in this work is introduced. In Section 4 we show the results of our simulations and discuss them. Finally, in Section 5 we present the main conclusions and future work.