The aim of this study is to test the applicability of snow surveying in the collection and detailed characterization of vehicle-derived magnetic particles. Road dust extracted from snow, collected near a busy urban highway and a low traffic road in a rural environment (southern Finland), was studied using magnetic, geochemical and micro-morphological analyses. Significant differences in horizontal distribution of mass specific magnetic susceptibility (χ) were noticed for both roads. Multi-domain (MD) magnetite was identified as the primary magnetic mineral. Scanning electron microscope (SEM) analyses of road dust from both roads revealed: (1) angular-shaped particles (diameter ∼1-300 μm) mostly composed of Fe, Cr and Ni, derived from circulation of motor vehicles and (2) iron-rich spherules (d ∼ 2-70 μm). Tungsten-rich particles (d < 2 μm), derived from tyre stud abrasion were also identified. Additionally, a decreasing trend in χ and selected trace elements was observed with increasing distance from the road edge. 相似文献
The size of particles in urban air varies over four orders of magnitude (from 0.001 μm to 10 μm in diameter). In many cities
only particle mass concentrations (PM10, i.e. particles <10 μm diameter) is measured. In this paper we analyze how differences
in emissions, background concentrations and meteorology affect the temporal and spatial distribution of PM10 and total particle
number concentrations (PNC) based on measurements and dispersion modeling in Stockholm, Sweden. PNC at densely trafficked
kerbside locations are dominated by ultrafine particles (<0.1 μm diameter) due to vehicle exhaust emissions as verified by
high correlation with NOx. But PNC contribute only marginally to PM10, due to the small size of exhaust particles. Instead
wear of the road surface is an important factor for the highest PM10 concentrations observed. In Stockholm, road wear increases
drastically due to the use of studded tires and traction sand on streets during winter; up to 90% of the locally emitted PM10
may be due to road abrasion. PM10 emissions and concentrations, but not PNC, at kerbside are controlled by road moisture.
Annual mean urban background PM10 levels are relatively uniformly distributed over the city, due to the importance of long
range transport. For PNC local sources often dominate the concentrations resulting in large temporal and spatial gradients
in the concentrations. Despite these differences in the origin of PM10 and PNC, the spatial gradients of annual mean concentrations
due to local sources are of equal magnitude due to the common source, namely traffic. Thus, people in different areas experiencing
a factor of 2 different annual PM10 exposure due to local sources will also experience a factor of 2 different exposure in
terms of PNC. This implies that health impact studies based solely on spatial differences in annual exposure to PM10 may not
separate differences in health effects due to ultrafine and coarse particles. On the other hand, health effect assessments
based on time series exposure analysis of PM10 and PNC, should be able to observe differences in health effects of ultrafine
particles versus coarse particles. 相似文献
INTRODUCTION: The purpose of this study was to examine the impact of a nationwide response to emerging airbag-related deaths among children. This response, implemented in 1996, focused on moving children to a rear seat and increasing proper restraint usage. METHOD: Fatality trends from 1992 through 1996 and from 1996 through 2003 were examined for younger children (ages 0-3) and for older children (ages 4-12). RESULTS: Prior to 1997, a steady reduction in unrestrained deaths (among younger children) was offset by increases in restrained deaths (among younger and older children), increases in rear-seat deaths (among younger children), and increases in front-seat deaths (among older children). After 1996, there were significant decreases in fatalities in both age groups, with larger and more immediate reductions among the younger children. The largest reductions were immediately after 1996, when younger-child deaths declined by 16%, and after 1999, when deaths among both age groups declined by about 16%. CONCLUSIONS: The immediate reduction in front-seat deaths among younger children, particularly infants, appears to have been closely associated with the nationwide public information efforts implemented in 1996. Later reductions in front-seat and unrestrained deaths, among both younger and older children, were likely associated with the combination of legislative, enforcement, and public information programs, which increased after 1999. IMPACT ON INDUSTRY: The findings suggest that a large expenditure of resources by public and private-sector organizations after 1996 resulted in the prevention of hundreds of deaths among young children. In addition, the results provide insights with regard to the categories of deaths most affected by such programs and issues that deserve additional attention. 相似文献
INTRODUCTION: Using data from the NASS General Estimates System (GES), the method of induced exposure was used to assess the effects of electronic stability control (ESC) on loss-of-control type crashes for sport utility vehicles. METHOD: Sport utility vehicles were classified into crash types generally associated with loss of control and crash types most likely not associated with loss of control. Vehicles were then compared as to whether ESC technology was present or absent in the vehicles. A generalized additive model was fit to assess the effects of ESC, driver age, and driver gender on the odds of loss of control. In addition, the effects of ESC on roads that were not dry were compared to effects on roads that were dry. RESULTS: Overall, the estimated percentage reduction in the odds of a loss-of-control crash for sport utility vehicles equipped with ESC was 70.3%. Both genders and all age groups showed reduced odds of loss-of-control crashes, but there was no significant difference between males and females. With respect to driver age, the maximum percentage reduction of 73.6% occurred at age 27. The positive effects of ESC on roads that were not dry were significantly greater than on roads that were dry. 相似文献
Objectives: During the past 2 decades, there have been large increases in mean horsepower and the mean horsepower-to–vehicle weight ratio for all types of new passenger vehicles in the United States. This study examined the relationship between travel speeds and vehicle power, defined as horsepower per 100 pounds of vehicle weight.
Methods: Speed cameras measured travel speeds and photographed license plates and drivers of passenger vehicles traveling on roadways in Northern Virginia during daytime off-peak hours in spring 2013. The driver licensing agencies in the District of Columbia, Maryland, and Virginia provided vehicle information numbers (VINs) by matching license plate numbers with vehicle registration records and provided the age, gender, and ZIP code of the registered owner(s). VINs were decoded to obtain the curb weight and horsepower of vehicles. The study focused on 26,659 observed vehicles for which information on horsepower was available and the observed age and gender of drivers matched vehicle registration records. Log-linear regression estimated the effects of vehicle power on mean travel speeds, and logistic regression estimated the effects of vehicle power on the likelihood of a vehicle traveling over the speed limit and more than 10 mph over the limit.
Results: After controlling for driver characteristics, speed limit, vehicle type, and traffic volume, a 1-unit increase in vehicle power was associated with a 0.7% increase in mean speed, a 2.7% increase in the likelihood of a vehicle exceeding the speed limit by any amount, and an 11.6% increase in the likelihood of a vehicle exceeding the limit by 10 mph. All of these increases were highly significant.
Conclusions: Speeding persists as a major factor in crashes in the United States. There are indications that travel speeds have increased in recent years. The current findings suggest the trend toward substantially more powerful vehicles may be contributing to higher speeds. Given the strong association between travel speed and crash risk and crash severity, this is cause for concern. 相似文献
Problem: The rollover crash is a serious crash type that often causes higher injury severities. Moreover, factors that contribute to the injury severities of rollover crashes may show instabilities in different vehicle types and time periods, which requires further investigations. This study utilizes the rollover crash data in North Carolina from Highway Safety Information System (HSIS) to study the effect instabilities of factors in vehicle type and time periods in rollover crashes. Methods: The injury severities of drivers are estimated using the random parameters logit (RPL) model with heterogeneity in means and variances. Available factors in HSIS have been categorized into three groups, which are drivers, road, and environment, respectively. This study also justifies the segmentations through transferability tests. The effects of identified significant factors are evaluated using marginal effects. Results: Factors such as FWP (farm, wood, and pasture areas), unhealthy physical condition, impaired physical condition, road adverse, and so forth have shown instabilities in marginal effects among vehicle types and time periods. Practical Applications: The finding of this research could provide important references for policy makers and automobile manufactures to help mitigate the injury severity of rollover crashes. 相似文献