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Crashes at signalized intersections account for approximately 20% of all crashes both nationally and within the State of Minnesota. Past research suggests that the use of all-red clearance interval at signalized intersections may reduce intersection crashes, particularly those related to signal violations. Other research suggests that this reduction may only be temporary. This research evaluates the safety effect of all-red clearance intervals at low speed urban four way intersections in the City of Minneapolis. The study includes a review of literature and assessment of Midwestern state and local practice related to the use of all-red phasing. A cross-section analysis using four years of data is presented, which does not substantiate any safety benefit of all-red phasing at study area intersections. Several regression models (generalized linear mixed models with Poisson error distribution and log link function and linear mixed models with transformed data) are also presented. The models also point to no safety benefit. A before and after analysis using 11 years of data was conducted to evaluate both short and long term effects. While results indicate short-term reductions in crash rates (approximately one year after the implementation), long-term reductions are not observed.

Report #1 in Developing Intersection Decision Support Solutions. Minnesota's rural crash records were analyzed in order to develop a better understanding of crashes at rural intersections and their cause. The objective in studying the causes of crashes at rural intersections is to support development of technology based strategies to mitigate high crash rates. Since previous research found that 80% of intersection crashes at thru-STOP intersections may be related to selection of insufficient gaps, the development and validation of Intersection Decision Support (IDS) technology that assists in proper gap selection was identified as a primary goal. A database of over 3,700 intersections was examined. Using the critical crash rate as an indicator, 23 rural expressway intersections and 104 rural two-lane intersections were identified as unusually "dangerous" locations. Right angle crashes (which are most often related to gap selection) were observed to account for approximately 50% of all crashes at the "dangerous" intersections, up from 28% for all rural thru-STOP intersections. A specific intersection was identified, evaluated and then selected for testing IDS technologies that can track vehicles approaching on the major roadway, compute the gap and communicate the information to drivers stopped on the minor street waiting to enter the intersection. The data acquisition system to be installed will allow analysis of driver decision making behavior and study the effects of introducing an IDS technology under development at the University of Minnesota.

Report #2 in the Series: Toward a Multi-State Consensus on Rural Intersection Decision Support. This project looked at various intersection data to find the best North Carolina intersection candidate for test deployment of Intersection Decision Support (IDS) technology, and found that US 74 and State Route 2210 is the best candidate.

Report #3 in the Series: Toward a Multi-State Consensus on Rural Intersection Decision Support. This project looked at various intersection data to find the best Michigan intersection candidate for test deployment of Intersection Decision Support (IDS) technology, and found that M-44 and Ramsdell Drive is the best candidate.

INV 805: This study evaluated the effectiveness of street lighting on isolated rural intersections in reducing nighttime crashes, using both a comparative analysis and a before-and-after study, and found that street lighting can reduce the number of crashes.

The Intersection Decision Support (IDS) research project is sponsored by a consortium of states (Minnesota, California, and Virginia) and the Federal Highway Administration (FHWA) whose objective is to improve intersection safety. The Minnesota team's focus is to develop a better understanding of the causes of crashes at rural unsignalized intersections and then develop a technology solution to address the cause(s). In the original study, a review of Minnesota's rural crash records and of past research identified poor driver gap selection as a major contributing cause of rural intersection crashes. Consequently, the design of the rural IDS technology has focused on enhancing the driver's ability to successfully negotiate rural intersections by communicating information about the available gaps in the traffic stream to the driver. In order to develop an IDS technology that has the potential to be nationally deployed, the regional differences at rural intersections must first be understood. Only then can a universal solution be designed and evaluated. To achieve this goal of national consensus and deployment, the University of Minnesota and the Minnesota Department of Transportation initiated a State Pooled Fund study, in which nine states are cooperating in intersection-crash research. This report documents the crash analysis phase of the pooled fund study for the State of Wisconsin.

This evaluation determined the change in crash frequency, type or severity associated with longitudinal sinusoidal rumble strips on rural two-lane undivided Minnesota roadways constructed between 2018 and 2022. Crash modification factors (CMFs) were estimated using cross-sectional analysis to compare crash experience of locations with sinusoidal rumble strips (i.e., centerline only, centerline and shoulder, or shoulder only) compared to roads with rectangular rumble strips. The cross-sectional analysis matched sites with sinusoidal and rectangular rumble strips using matched-pair comparisons. Negative binomial (NB) or Poisson log-linear regression models were used to model the crashes at all treatment and non-treatment sites. There was a total of approximately 327 miles of treated (i.e., centerline only, centerline and shoulder, or shoulder only sinusoidal rumble strips) and approximately 302 miles of untreated (i.e., centerline only, centerline and shoulder, or shoulder only rectangular rumble strips) on rural two-lane divided roads. Overall, the results of the models indicated no significant differences in crash rates between rural two-lane undivided roads with sinusoidal rumble strips, and rural two-lane undivided roads with rectangular rumble strips.

Report #6 in the series: Toward a Multi-State Consensus on Rural Intersection Decision Support. This is the sixth in a series of reports sponsored by a consortium of nine states and the Federal Highway Administration to improve intersection safety. To develop an Intersection Decision Support (IDS) technology that potentially can be deployed nationally, regional differences at rural intersections must be understood. To achieve this goal, the University of Minnesota and Mn/DOT conducted a State Poled Fund Study. This report documents the crash analysis phase of the Pooled Fund Study for the State of New Hampshire and concludes that the intersection that is the best overall candidate for test deployment of the IDS Vehicle System is NH 101 and HN 123.

Report #7 in the Series: Toward a Multi-State Consensus on Rural Intersection Decision Support. This is the seventh report in a series that will be used to understand the regional differences in rural intersection crashes. It documents the initial crash-analysis phase of a nine-state pooled fund study for Nevada and concludes that the best overall candidate for test deployment of the IDS vehicle surveillance system is US 50 and Sheckler Cutoff.

Report #4 in the Series: Toward a Multi-State Consensus on Rural Intersection Decision Support. The Intersection Decision Support (IDS) research project is sponsored by a consortium of states (Minnesota, California, and Virginia) and the Federal Highway Administration (FHWA) whose objective is to improve intersection safety. The Minnesota team's focus is to develop a better understanding of the causes of crashes at rural unsignalized intersections and then develop a technology solution to address the cause(s). In the original study, a review of Minnesota's rural crash records and of past research identified poor driver gap selection as a major contributing cause of rural intersection crashes. Consequently, the design of the rural IDS technology has focused on enhancing the driver's ability to successfully negotiate rural intersections by communicating information about the available gaps in the traffic stream to the driver. In order to develop an IDS technology that has the potential to be nationally deployed, the regional differences at rural intersections must first be understood. Only then can a universal solution be designed and evaluated. To achieve this goal of national consensus and deployment, the University of Minnesota and the Minnesota Department of Transportation initiated a State Pooled Fund study, in which nine states are cooperating in intersection-crash research. This report documents the crash analysis phase of the pooled fund study for the State of Iowa.