Browsing by Author "Gao, Jingru"

Now showing 1 - 6 of 6
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    Criteria and Guidelines for Three-Lane Road Design and Operation
    (Minnesota Department of Transportation, 2023-02) Davis, Gary A.; Hourdos, John; Gao, Jingru
    A 4-3 conversion involves changing a four-lane undivided road into one with two general travel lanes separated by a two-way left turn lane. A commonly-used guideline states that a 4-3 conversion can be considering as long as the road’s average annual daily traffic (AADT) volume does not exceed 15,000 vehicles/day but opinions vary, from lowering the AADT threshold to 10,000 vehicles/day to anecdotal evidence for successful 4-3 conversions with AADTs as high as 20,000. The main objective of this project was to identify conditions where 4-3 conversions might be feasible at AADTs greater than 15,000. After reviewing the literature, we conducted simulation studies on three different roads to identify combinations of major and minor road flow where three-lane configurations provided acceptable levels of service. Eight intersections, with 16 approaches, were then selected to represent our findings. These results were presented as summary tables that practitioners could use to make initial assessments regarding 4-3 conversion feasibility.
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    Developing and Validating a Model of Left-Turn Crashes to Support Safer Design and Operations
    (Center for Transportation Studies, University of Minnesota, 2018-09) Davis, Gary; Gao, Jingru; Mudgal, Abhisek
    This report documents work done to advance the state of art in crash simulation. This includes: (1) A field study to collect data on drivers’ left-turn gap acceptance and turning times, and development of statistical models that can be incorporated into a crash simulation model; (2) The use of Markov Chain Monte Carlo computational tools to quantify uncertainty in planar impact reconstruction of two-vehicle crashes; (3) A method for combing the results from planar impact reconstruction with event data recorder pre-crash data to estimate descriptive features of actual left-turn crashes. This is applied to several left-turn crashes from the National Highway Traffic Safety Administration’s NASS/CDS database; (4) A left-turn crash simulation model incorporating the above results. Initial model checking is performed using estimates from the reconstructed NASS/CDS cases as well as results from a previous study on left-turn crash risk. Also described is a method for simulating crash modification effects without having to first simulate crashes as rare outcomes in very large numbers of gap acceptances.
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    Driver Comprehension of Flashing Yellow Arrows
    (Minnesota Department of Transportation, 2023-12) Davis, Gary A.; Stern, Raphael; Duhn, Melissa; Gao, Jingru
    In 2009, the FHWA's Manual on Uniform Traffic Control Devices (MUTCD) introduced the flashing yellow arrow (FYA) traffic signal as an alternative to circular green (CG) to indicate permitted left turns. The FYA is arguably a more intuitive indication that left turns are permitted but not protected and, in addition, the FYA signal heads can support time-of-day changes between protective and permissive left -turn phasing. In 2019, a Research Needs Statement stated that "Research is needed to examine driver comprehension of flashing yellow arrows in different light arrangements and the role of signage." Our objective in this project was to assess drivers' understanding of FYA signal indications and to see if the presence or absence of "Left Turn Yield" signs affect gap acceptance. This was accomplished by conducting an online survey of drivers regarding their understanding of FYA signals and by carrying out a field study of drivers' gap acceptance at a set of Twin Cities intersections.
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    Safety Impacts of the I-35W Improvements Done Under Minnesota’s Urban Partnership Agreement (UPA) Project
    (Minnesota Department of Transportation, 2017-06) Davis, Gary A.; Gao, Jingru; Hourdos, John
    As part of an Urban Partnership Agreement project, the Minnesota Department of Transportation added lanes and began operating a priced dynamic shoulder lane (PDSL) on parts of Interstate 35W. Following the opening of these improvements, the frequency of rear-end crashes increased in certain sections, especially in the PDSL region. The object of this study was to determine if these increases were direct effects of the improvements or were due to changes in traffic conditions. Logistic regression analyses which controlled for changes in traffic conditions indicated no direct effect on the likelihood of rear-end crashes due to operation of the PDSL; the observed change in crash frequency was explained by the change in traffic conditions. This study also found evidence for a nonlinear relationship between a proxy for traffic density, lane occupancy, and the probability of a rear-end crash occurring during an hour. In several sections crashes were most likely when lane occupancies were approximately 20%–30%, and crash likelihood tended to decrease for lane occupancies below and above this range.
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    Safety Study of I-35W Improvements Done Under Minnesota’s Urban Partnership Agreements (UPA) Project
    (2017-08) Gao, Jingru
    Minnesota’s Urban Partnership Agreements (UPA), of which the majority were completed in November, 2010, consisted of a series of improvements addressing the congestion on Interstate highway I-35W corridor and in Downtown Minneapolis. MnDOT Problem Statement NS-329 noted that there was interest in extending some or all of these interventions to other corridors and called for an estimation of their safety effects to assist in making these decisions. Following the UPA, the frequency of rear-end crashes increased substantially in certain regions on I-35W. The objective of this study was to determine if the increase in crash frequency was due to changes in traffic conditions or was a direct effect of the UPA interventions. A preliminary analysis was done to determine priority crash type and study regions. I-35W, from its start to its junction with I-94, was divided into 17 one-mile sections, and bi-directional (northbound and southbound) crash frequencies in Before-UPA (2006-2008) and After-UPA periods (2011-2013) were compiled for each one-mile section. Rear-end crash turned out to be the most prevalent crash type, but the changing trend of bi-direction rear-end crash frequencies from the Before to After period varied among those one-mile sections. Our interest lay in those regions where there was an outstanding increase in the rear-end crash frequency in the After period, which were approximately the I-35W HOT region (from TH-13 to I-494) and the I-35W PDSL region (from 37th Street to 26th Street). Both the I-35W HOT and PDSL regions were divided into analysis sections based on constant flow and geometry criteria as well as the loop detector availability. Crash, loop detector, weather condition, and PDSL activation (only for PDSL sections) were compiled for Before and After periods for each analysis section. Rear-end crash records were extracted using MNCMAT, and hard copies of the original crash reports were then reviewed to verify the crash type, location, direction and time for each crash. Traffic conditions came from loop detector data retrieved using MnDOT’s DataExtract tool. The source of weather conditions during non-crash hours was MnDOT’s RWIS, while that of weather conditions during crash hours were taken from original crash reports. The PDSL historical operation data came from MnDOT’s log for the Intelligent Lane Control Signal (ILCS) located at 37th Street. Logistic regression models were established to estimate the change in rear-end crash risk in a given hour before and after the UPA project controlling for changes in traffic conditions and weather conditions. The analysis results showed that: (1) Most analyzed sections in the I-35W HOT region showed no significant change in rear-end crash risk associated with the UPA project except for Section S9 (southbound, just north of Minnesota River). Section N17 actually experienced fewer crashes after the UPA project, but the reduction was not as great as the change in lane occupancy would predict. (2) The PDSL region experienced substantial increase in traffic congestion following the completion of UPA interventions. This was due to the removal of the old TH 62 & I-35W bottleneck, causing the bottleneck move northward to the I-35W & I-94 junction. The observed increase in rear-end crash risk was not associated with the operation of PDSL when controlling for the changes in traffic conditions. (3) An “inverted U” relationship between rear-end crash risk and a proxy for traffic density, lane occupancy, when controlling for other factors, were seen in most of the analysis sections. Rear-end crashes were most likely when lane occupancies were approximately 20%-30%. This study demonstrated a methodology that could be used to evaluate the safety effects of freeway-related projects. To be more specific, this study worked out a way to estimate changes in hourly crash risk while controlling for variations in traffic conditions.
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    Vehicle Automation and Transportability of Crash Modification Factors
    (Center for Transportation Studies, University of Minnesota, 2019-07) Davis, Gary A; Gao, Jingru
    Although the Highway Safety Manual (HSM) now provides empirical tools for predicting the safety consequences of highway engineering decisions, these tools represent the prevailing driver and vehicle conditions in the United States during the last few decades. As automated vehicles improve in capability and increase in market share, these conditions will change, possibly affecting the accuracy of HSM predictions. This report investigates the feasibility of using “transportability” analyses, developed by Judea Pearl and Elias Bareinboim, to assess the “transferability” of crash modification factors (CMF) to new situations. An overview in Chapter 2 concludes that transportability analysis is, in principle, possible provided one can describe a causal mechanism that explains how a CMF works. Chapter 3 then describes developing such an explanation for pedestrian hybrid beacons (PHB). In Chapter 4 the explanatory model developed in Chapter 3 is used to assess the transportability of existing estimates of PHB CMFs to a hypothetical situation where vehicles with autonomous braking are present.