Work zone safety continues to be one of the important focus areas for transportation agencies. Previous studies have identified that vehicle speed and lighting conditions are significant risk factors impacting work zo...Work zone safety continues to be one of the important focus areas for transportation agencies. Previous studies have identified that vehicle speed and lighting conditions are significant risk factors impacting work zone safety. </span><span style="font-family:Verdana;">This study evaluated the impact of the use of presence lighting and digital </span><span style="font-family:Verdana;">speed limit trailers on nighttime motorist speeds using commercially available connected vehicle speed data. Geospatial analysis was conducted on over 500,000 connected vehicle records to linear reference nearly 18,000 records from 195 unique trajectories to study section during the study period of 2 days. Results showed that median speeds reduced by 4 to 13 mph from 11PM to 7AM during the deployment of presence lighting and speed limit trailers </span><span style="font-family:Verdana;">compared to base conditions. A Kolmogorov-Smirnov (KS) statistical test</span><span style="font-family:Verdana;"> com</span><span style="font-family:Verdana;">paring 105 vehicles traveling through the construction zone with presence</span><span style="font-family:Verdana;"> lighting and speed limit trailers with a group of 90 vehicles during base condition indicated the speeds during the deployment of presence lighting and speed limit trailers were lower than the base condition. Also, increased compliance with the 55 mph speed limit was observed when the presence lighting and digital speed limit trailers were deployed. However, there were two hours (3AM to 5AM) where speeds increased by 0</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:Verdana;">4 mph, perhaps due to the low volume at that hour. The encouraging results support the further deployment of presence lighting and speed limit trailers in nighttime construction zones for reducing vehicle speeds. Those future deployments should be monitored with connected vehicle speeds to collect additional data to broaden the evaluation of these speed mitigation techniques over a diverse set of construction zone activities.展开更多
This study investigates relationships between congestion and travel time performance metrics and crashes on road segments. The study focuses on work zone routes in Iowa, utilizing 2021 commercially-available probe veh...This study investigates relationships between congestion and travel time performance metrics and crashes on road segments. The study focuses on work zone routes in Iowa, utilizing 2021 commercially-available probe vehicle data and crash data. Travel time performance metrics were derived from the probe vehicle data, and crash counts were obtained from the crash data. Additional variables included road characteristics (traffic volume, road type, segment length) and a categorical variable for the presence of a work zone. A mixed effect linear regression model was employed to identify relationships between road segment crash counts and the selected performance metrics. This was accomplished for two sets of models that include congestion performance measures at different defining threshold values, along with travel time performance measures. The study results indicate that the congestion indicators, certain travel time performance measures, and traffic counts were statistically significant and positively correlated with crash counts. Indicator variables for rural interstate locations and non-active work zones have a stronger influence on crash count than those for municipal interstate locations and active work zones. These findings can inform decision-makers on work zone safety strategies and crash mitigation planning, especially in high traffic volume areas prone to congestion and queues.展开更多
In this paper, a two-dimensional nanometer scale tip-plate discharge model has been employed to study nanoscale electrical discharge in atmospheric conditions. The field strength dis- tributions in a nanometer scale t...In this paper, a two-dimensional nanometer scale tip-plate discharge model has been employed to study nanoscale electrical discharge in atmospheric conditions. The field strength dis- tributions in a nanometer scale tip-to-plate electrode arrangement were calculated using the finite element analysis （FEA） method, and the influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of effective discharge range （EDR） on the plate were also investigated and discussed. The simulation results show that the probe with a wide tip will cause a larger effective discharge range on the plate; the field strength in the gap is notably higher than that induced by the sharp tip probe; the effective discharge range will increase linearly with the rise of excitation voltage, and decrease nonlinearly with the rise of gap length. In addition, probe dimension, especially the width/height ratio, affects the effective discharge range in different manners. With the width/height ratio rising from 1 ： 1 to 1 ： 10, the effective discharge range will maintain stable when the excitation voltage is around 50 V. This will increase when the excitation voltage gets higher and decrease as the excitation voltage gets lower. Fhrthermore, when the gap length is 5 nm and the excitation voltage is below 20 V, the diameter of EDR in our simulation is about 150 nm, which is consistent with the experiment results reported by other research groups. Our work provides a preliminary understanding of nanometer scale discharges and establishes a predictive structure-behavior relationship.展开更多
文摘Work zone safety continues to be one of the important focus areas for transportation agencies. Previous studies have identified that vehicle speed and lighting conditions are significant risk factors impacting work zone safety. </span><span style="font-family:Verdana;">This study evaluated the impact of the use of presence lighting and digital </span><span style="font-family:Verdana;">speed limit trailers on nighttime motorist speeds using commercially available connected vehicle speed data. Geospatial analysis was conducted on over 500,000 connected vehicle records to linear reference nearly 18,000 records from 195 unique trajectories to study section during the study period of 2 days. Results showed that median speeds reduced by 4 to 13 mph from 11PM to 7AM during the deployment of presence lighting and speed limit trailers </span><span style="font-family:Verdana;">compared to base conditions. A Kolmogorov-Smirnov (KS) statistical test</span><span style="font-family:Verdana;"> com</span><span style="font-family:Verdana;">paring 105 vehicles traveling through the construction zone with presence</span><span style="font-family:Verdana;"> lighting and speed limit trailers with a group of 90 vehicles during base condition indicated the speeds during the deployment of presence lighting and speed limit trailers were lower than the base condition. Also, increased compliance with the 55 mph speed limit was observed when the presence lighting and digital speed limit trailers were deployed. However, there were two hours (3AM to 5AM) where speeds increased by 0</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:Verdana;">4 mph, perhaps due to the low volume at that hour. The encouraging results support the further deployment of presence lighting and speed limit trailers in nighttime construction zones for reducing vehicle speeds. Those future deployments should be monitored with connected vehicle speeds to collect additional data to broaden the evaluation of these speed mitigation techniques over a diverse set of construction zone activities.
文摘This study investigates relationships between congestion and travel time performance metrics and crashes on road segments. The study focuses on work zone routes in Iowa, utilizing 2021 commercially-available probe vehicle data and crash data. Travel time performance metrics were derived from the probe vehicle data, and crash counts were obtained from the crash data. Additional variables included road characteristics (traffic volume, road type, segment length) and a categorical variable for the presence of a work zone. A mixed effect linear regression model was employed to identify relationships between road segment crash counts and the selected performance metrics. This was accomplished for two sets of models that include congestion performance measures at different defining threshold values, along with travel time performance measures. The study results indicate that the congestion indicators, certain travel time performance measures, and traffic counts were statistically significant and positively correlated with crash counts. Indicator variables for rural interstate locations and non-active work zones have a stronger influence on crash count than those for municipal interstate locations and active work zones. These findings can inform decision-makers on work zone safety strategies and crash mitigation planning, especially in high traffic volume areas prone to congestion and queues.
基金supported in part by External Cooperation Program of Chinese Academy of Sciences(No.GJHZ1218)National Natural Science Foundation of China(No.61004133)SSSTC JRP awards 2011(IZLCZ2 138953)
文摘In this paper, a two-dimensional nanometer scale tip-plate discharge model has been employed to study nanoscale electrical discharge in atmospheric conditions. The field strength dis- tributions in a nanometer scale tip-to-plate electrode arrangement were calculated using the finite element analysis （FEA） method, and the influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of effective discharge range （EDR） on the plate were also investigated and discussed. The simulation results show that the probe with a wide tip will cause a larger effective discharge range on the plate; the field strength in the gap is notably higher than that induced by the sharp tip probe; the effective discharge range will increase linearly with the rise of excitation voltage, and decrease nonlinearly with the rise of gap length. In addition, probe dimension, especially the width/height ratio, affects the effective discharge range in different manners. With the width/height ratio rising from 1 ： 1 to 1 ： 10, the effective discharge range will maintain stable when the excitation voltage is around 50 V. This will increase when the excitation voltage gets higher and decrease as the excitation voltage gets lower. Fhrthermore, when the gap length is 5 nm and the excitation voltage is below 20 V, the diameter of EDR in our simulation is about 150 nm, which is consistent with the experiment results reported by other research groups. Our work provides a preliminary understanding of nanometer scale discharges and establishes a predictive structure-behavior relationship.
