Some studies, for example, analyzed the distances of certain locations as indicator, such as that from one's residence or school to the streets, or the density of vehicles or length and density of streets in census tracts or buffers, while others used the flow of vehicles on streets of interest, or used a combination of several indicators. The outcomes evaluated in these studies varied between heart diseases , respiratory diseases 5, , gestational outcomes , allergies and changes in the immunological system , thrombosis 32 , cancer and leukemia , lead contamination 38 and mortality in general Studies on the exposure to vehicular traffic using distance as the only indicator.
This method consisted in the use of GIS to map a place of interest and its distance to one or more streets. The majority of studies evaluated the exposure from the home or school address 11 , or from a certain point of reference, such as the census tract centroid 6. Exposure was based on the distance from these points to the streets and it served as parameter to infer the level of exposure experienced by individuals.
Certain studies only considered the nearest road ,11,12,25,32 ; others used the main road arterial roads, collector streets considered to have high traffic intensity 6,18,20,26,28 ; yet others were based on the distance of both types of road - road or main road 5,14,17,19,31, Certain authors used the shortest distance from the point of interest to a road to evaluate the exposure of individuals in their studies 6,9,25,26, Other authors considered individuals whose distance was lower than a certain value to be exposed, a value that ranged from 50 m 5,12,39 , m 5,18,20,31,39 , m 18,19,23,31 , m 7,20,28,31 , m 17,19 up to m Some studies evaluated certain distances according to road classification: Hoek et al.
Kim et al. Studies on the exposure to vehicular traffic using its intensity as the only indicator.
Many studies used exposure to vehicular traffic intensity as their method to evaluate exposure, understood as the number of vehicles passing through a certain road, during a specific period of time. The majority considered the annual mean of daily traffic and only Wyler et al. The majority were based on vehicular traffic in relation to the homes of individuals. One study considered the place of work 38 and another one, schools The values of vehicle flow were obtained by general count, not specifying the type of vehicle, except for the studies by Janssen et al.
A total of three studies applied questionnaires and obtained the self-reported traffic intensity on the street of residence 15,20, In another methodological approach, the measure of traffic was obtained by multiplying the length of roads close to the homes of the population studied by the daily mean of vehicle flow on such roads 16,21,35, There were two studies, obtained in the review, that were not limited exclusively to data on the distance of roads or vehicular traffic to evaluate exposure, but they also calculated the density of roads and vehicles in the polygon that surrounded the home.
Based on the individual's geocoded address and census data, Reynolds et al. The density of vehicles referred to the number of vehicle owners in a census tract, rather than its circulation on the roads of this area. The density of vehicles provides an estimate of the potential of exposure to emissions from fuel evaporation when vehicles are parked at night, once such evaporation is an important source of organic volatile gases, such as benzene For the calculation of the density of roads, the total length of roads of an area unit known as buffered blocks was divided by its area.
These buffered blocks consisted of an additional frontier of m around each census tract. According to authors, the increase in the frontier of census tracts prevented a discrepancy in the size of the area and roads of such sectors in the calculation of this measure. In another study conducted by Reynolds et al. Utilization of more than one indirect measure of exposure to vehicular traffic in the same study.
Many studies used the combination of several indicators of exposure to vehicular traffic to indirectly estimate atmospheric pollution. One methodology which was repeatedly observed is based on the combination of data on the flow of vehicles and the distance of roads around the point of interest representing the dispersion of pollutants resulting from vehicles, from the street center.
The higher the flow on the road, the greater the emission of vehicle pollutants, increasing the concentrations of such pollutants in the urban space, especially in the homes close to busier roads. For each individual studied, the DWTD is calculated according to a varying distance around their home or another geocoded place of interest Figure 2 , where W is the buffer width and D is the shortest distance from one's home to each road within the buffer. Y is the value used to weigh the vehicle flow obtained for each road within this area. Then, the vehicle flow of such street is divided by the Y value, generating an X value.
Next, the weighted values of traffic X of all roads included in the buffer n are added, thus obtaining the DWTD. As the density and characteristics of constructions, predominant wind direction, altitude, and turbulence caused the flow of vehicles to affect the dispersion of pollutants generated by traffic, various buffer widths could be assumed to calculate the DWTD. This reduces lack of accuracy in the measure of exposure. Studies used buffers with a radius varying from m 13,17,18 , feet As observed in the literature search, the road network and its respective vehicle flow is an important indicator of atmospheric pollution, once mobile sources are the main producers of emissions of such pollutants in urban areas.
However, when the distance of roads or the volume of traffic represent only the road that is closest to one's home, the evaluation of exposure may have limitations, because a more distant road with heavy traffic could be important for the analysis.
Thus, the weighting of vehicle flow by the distance enables a more reliable evaluation, as it considers the set of roads that surround one's home. Only some studies were based on a single method of evaluation of exposure, the majority of authors sought to use several or to combine them. Despite this variety and combinations, few studies considered more detailed traffic information, such as the mean speed of vehicles 38 , the type of vehicle cars or trucks and what could characterize the fuel used 40 , and none considered the year the vehicle was manufactured.
It was observed that only two reviewed studies included the discrimination between truck traffic and that of the remaining vehicles during data analysis 11, All types of automotive vehicles produce pollutants that affect the quality of air; however, the type of fuel used by these vehicles determines a higher or lower concentration of different pollutants, which, in different ways, lead to adverse effects on health. The majority of articles shown did not include the residential mobility variable in the analyses, nor the time spent by individuals in their residence, place of work or when going from their residence to work.
Residential mobility was analyzed by Hooven et al. Of all the 7, pregnant women participating in this study, only 1, One limitation pointed out by Reynolds et al. On the other hand, Miyake et al. A total of two interviews were conducted with the pregnant women, one in the prenatal period and the other between the 2 nd and 9 th months after birth.
Of all women, Shima et al. Of all the 3, individuals who responded the first questionnaire, Another limitation in several reviewed articles is the temporal resolution of traffic data. Pearson et al. Thus, the estimates could not correspond to the period before the diagnosis of cancer for each child, and these may have moved from their home during the period of study. Authors stated that this last fact could be confirmed in a previous study, which indicated that many children had in fact moved. Langholz et al. The traffic count that was closest to the period of selection of individuals cases occurred between and , and the most etiologically relevant period for the study was before the date of diagnosis exposure of children between and , before the diagnosis of leukemia , i.
Wilhelm and Ritz 24 and Hooven et al. One advantage of the study performed in France by Zmirou et al. When road classification roads, arterial and collection roads is the only factor taken into consideration to evaluate exposure, it is not possible to identify, for example, possible variations in the same classification, once estimated traffic values are standardized within ranges of values. Larger roads with heavier traffic, such as highways and main roads, have been exhaustively considered in studies 10,11,17, However, local roads were not so frequently included, and when such roads were analyzed, the values of their vehicle flows were not observed in a more detailed way, with the adoption of a single value.
Information about the proportion of local roads, when compared to others, is important, because it enables the identification of the actual need for such roads to be analyzed or not, especially when it comes to a residential area. Only one study considered all types of roads, including the traffic of local roads Differently from other authors, who did not analyze local roads or attributed a single value to them all, Medeiros et al. The difference in concentration of pollutants inside and outside of a home could be questioned as a limiting factor of studies that estimate the exposure of the population, based on an indicator of vehicular traffic.
However, Hoek et al. Another aspect that could be questioned is whether the type of road or even its vehicle flow is an adequate indicator of the level of pollution in the area.
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History of Reducing Air Pollution from Transportation in the United States One result of the rapid increase of motor vehicles was air pollution, especially in. The addition of many thousands of cars on the road in the years after World War II intensified the spread of air pollution, added more and newer sources of.
First, between and , the NOx standard becomes 2. Then in , the NOx standard for cars is reduced to 1. Effective in , EPA then sets the first tailpipe standards for heavier trucks at 1. The NOx standard is set at 0. The new standard called "Tier 1"is a 40 percent reduction from the standard.