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SAFETY AND OPERATION EVALUATION OF MOVING WORK ZONES
Liu, Lanxi
Liu, Lanxi
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Abstract
Moving work zones (MWZs) are frequently implemented to meet the requirements of routine road maintenance tasks. During the MWZ operation, workers and equipment move at speeds of 15 mph or slower, potentially disrupting regular traffic flow and causing traffic congestion and safety concerns, however, factors contributing to heightened risk of crashes or severe crashes, and congestion, have not been thoroughly studied. In this study, spatial analysis, logistic regression, and VISSIM simulation were applied to better understand the contributing factors.
In the spatial analysis, the output of multiple spatial tools, including the Average Nearest Neighbor (ANN), Global Moran’s I, and Getis-Ord General G methods, all indicated that MWZ crashes exhibited clustering in Kansas. The Getis-Ord (Gi∗) method and Anselin Local Moran's I method identified the hot spots of MWZ crashes primarily in Douglas, Johnson, Wyandotte, eastern Shawnee, southern Leavenworth, southern Harvey, Sedgwick, and western Butler, with a 99% confidence level. Anselin Local Moran's I also discovered low-low clusters, low-high outliers, and high-low outliers. The analysis of MWZ crashes in identified hot spots indicated that MWZ crashes predominantly occurred in rural areas, near intersections, on road shoulders, on two-lane roadways, and included large commercial vehicles. The evaluation of hotspots and H-L outliers indicated that the likelihood of MWZ crashes was markedly greater on roads with speed limits above 55 mph. The observed high-probability factors may contribute to MWZ crashes, thus requiring further investigation to determine their impact and significance level.
Logistic regression models were employed to identify distinct factors of MWZ crashes in comparison to other types of work zone crashes and to determine significant variables associated with medium or high crash severity. The probability of MWZ crashes occurring on roadways with speed limits over 45 mph was much higher than that of other work zone crashes, with an odds ratio indicating that the likelihood of MWZ crashes was five times greater compared to non-MWZ crashes when the speed limit exceeded 65 mph. Other road conditions, such as rumble strips and traffic signals were identified as factors that reduced the likelihood of MWZ crashes, primarily by lowering vehicle speeds and regulating traffic flow. Driver behaviors, including speeding, disregarding traffic control and driver fatigue, were determined to escalate the severity of MWZ crashes by 5 times, 3.1 times and 9.6 times, respectively. Large commercial vehicle involvement doubled the likelihood of MWZ crashes and doubled the likelihood of causing high/medium severity crashes compared to low severity, whereas motorcycle involvement increased the probability of high/medium severity MWZ crashes by 15 times. KDOT District 2 and rural areas were identified as contributing factors to the increased likelihood of MWZ crashes, with rural areas exhibiting a more than twofold increase in the risk of resulting in high or medium severity crashes compared to urban areas, necessitating additional attention from KDOT regarding MWZ operations in these regions.
The simulation model developed in VISSIM confirmed the disruption of regular traffic flow by MWZ operations based on the performance measures including travel time, average speed, delay, and stops. The MWZ operational period may be chosen to correspond optimal road conditions for MWZ operation on a four-lane freeway if allowed by the nature of the work, which were determined to be: a traffic volume of less than 1,000 vehicles per hour per lane, a speed limit of 55 mph, and a truck percentage below 10%. The optimal operational speed for MWZ is above 10 mph, ideally reaching 15 mph, to minimize disruptions. The roll-ahead distance was observed to have a negligible impact on mobility and should be established in accordance with DOT recommendations accounting for vehicle speed, speed limitations, and the weight of the impacting vehicle. Under the recommended conditions, the resulted performance measures are: travel time of 1,318 seconds, average speed of 54.6 mph, average delay of 10.8 seconds, and 0 stops, which mitigated traffic delays and avoided vehicle stops.
This study helped understand the spatial pattern of MWZ crashes, interpreted the crash characteristics, assessed the contributing factors to MWZ risk and crash severity and, and evaluated MWZ operating conditions to increase mobility. The findings of this study can be employed to forecast MWZ crash occurrences and their severity, and improve MWZ management strategies to mitigate congestion and risk.
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Date
2024-01-01
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University of Kansas
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This item contains archived web content.
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Liu_ku_0099D_19897.pdf
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- Embargoed until 2174-05-31
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Keywords
Transportation, Logistic Regression, Mobility, Moving Work Zone, Safety, Spatial Analysis, VISSIM