Search Content

Between 2018 and 2019, MnDOT installed a lane constrictor design at 66 side-street, stop-controlled intersections in Minnesota. The lane constrictor design narrows the lane width for mainline approaches via a striped median with centerline rumble strips. By narrowing the mainline lane, the goal of this design is to encourage mainline traffic to slow down as it approaches the intersection. The striped median also provides greater separation between mainline directions and draws more attention to the location of the intersection. Following the installation of lane constrictors at MnDOT intersections, overall crash rates have seen little change but there have been decreases in fatal and serious injury (KA) as well as fatal and all injury (KABC) crash rates. These results indicate the addition of lane constrictors have a positive impact on crashes by reducing the severity of crashes, swapping injury crashes for property damage only crashes.

This report presents an approach to assess the effect of vehicle traffic volumes and speeds on pedestrian safety. It shows that the probability of standardized pedestrian conflict resulting in a collision can be computed given data on the distribution of vehicle speeds and headways on a residential street. Researchers applied this method to data collected on a sample of 25 residential streets in the Twin Cities and found that collision rates varied between 4 and 64 collisions per 1,000 pedestrian conflicts, depending primarily on the street's traffic volume. Using a model that relates the impact speed of a vehicle to the severity of pedestrian injury, they computed the probabilities of a severe collision. Sensitive to both traffic volume and traffic speed, the severe collision rate varied between 1 and 25 collisions per 1,000 conflicts. Using the same data, researchers also computed the crash reduction factor, used to assess the potential safety effect of a 25 miles per hour speed limit on the sample of residential streets. The estimated crash reductions ranged between .2% and 45%, depending primarily on the degree to which the vehicle speeds currently exceeded 25 miles per hour. Researchers also showed how this computation assists with the reconstruction of actual vehicle/pedestrian collisions.

A driving simulation experiment was conducted to research interventions to right-angle crashes at rural Thru-STOP intersections, which accounted for 71% of Minnesota fatal crashes in 1998, 1999, and the first half of 2000. The interventions caused drivers to reduce speed as they neared the intersection, and implies that 1) drivers are less likely to inadvertently run stop signs when slowing down further from the intersection, 2) making the intersection more noticeable improves driver safety judgment, and 3) speed reductions on the major road of an intersection produce greater reductions in stopping distances.

This report aims at establishing a correlation between the voluntary ISO 9000 certification by motor carriers and traffic safety. The report shows that improvement of operating and quality performance improved safety performance. As part of the analysis, several ISO 9000 certified and non-certified motor carrier companies were compared based on their social and financial performance prior to, during and after the certification process. The authors have shown that there is a positive increase in performance during and after the certification process. The number of motor carrier companies certified by ISO 9000 is limited and unique. The uniqueness arises from the fact that the certified organizations haul specialized products such as automobiles and hazardous materials. That shows that most organizations are certified due to mandatory reasons. In conclusion, the observations and results have thrown light in a new direction that indicates that there exists a significant relationship between the quality assurance and safety performance of a motor carrier organization. The authors feel that further research is necessary to investigate the circumstances under which ISO 9000 and other programs for upgrading motor carrier performance help lead to an increase in safety.

This study presents statistically reliable conclusions based on a comparison of the operational and safety characteristics of rural intersections without turning lanes, with bypass lanes, and with left turn lanes. The basic work tasks associated with the research study included: a literature search of nationally published research reports, a survey of bypass lane use, a summary of the legal issues associated with passing on the right, operations and safety analyses, and a review of Minnesota Department of Transportation (Mn/DOT) recommended design guidelines and design features. The results of the safety and operations analyses did not offer a high degree of statistical reliability. However, a comparative crash analysis and a before-versus-after analysis suggested that it is impossible to conclude that the use of a bypass lane provides a greater degree of safety, and, therefore, bypass lanes should not be used as a safety device. There also were some concerns expressed about safety issues at four-legged intersections. Recommendations included: Revise Mn/DOT turn lane policies to at least reduce or eliminate the use of bypass lanes at four-legged intersections; Consider developing a shorter and less costly exclusive left turn lane design; and Offer designers positive guidance regarding the use of left-turn lanes, through a prioritized approach based on the functional classification of the major roadway.

This report describes a Bayesian method for estimating accident rates at individual sites, which takes into account the fact that the total traffic count usually used to measure exposure is generally not known with certainty. The first step involves deriving an approximation for the probability of distribution of total traffic conditioned on a short count sample. This approximation is then used to derive a Bayes estimator of a site's accident rate, conditioned on an accident count, a short count sample, and the total traffic approximation. The method then uses Gibbs sampling to compute accident rate estimates. Tests based on actual accident and traffic data revealed that accident rate estimates based on a two-week traffic sample area are almost as accurate as estimates based on full traffic counting, but that uncertainty in the estimated accident rates increase by 20 to 50% when using a two-day count sample.

In Minnesota snow presents a special problem for rural mailbox installations. So, Minnesota Department of Transportation (Mn/DOT) developed cantilevered mailbox support designs. Recent studies had shown that certain rural mailbox installations easily penetrated the passenger compartment of an impacting vehicle. These same studies pointed out that a large number of people are seriously injured or killed each year as a result of mailbox collisions Therefore, Mn/DOT initiated full scale crash test to ascertain the crashworthiness of its cantilevered design. The study results were: 1. The change in vehicle momentum was below the recommended limit. 2. The test vehicle remained upright with no tendency to spin out or roll over. (The four by four wood vertical support was not hit . Studies by others adequately document vehicle/post interaction) . 3. The windshield was broken in each test. However, no part of the test article penetrated into the passenger compartment. 4. There was no appreciable difference between the support designs- The study concluded that the Mn/DOT cantilevered designs are acceptable in terms of nationally recognized criteria. Some precautions are also given as to use and placement of the supports.

Traffic data from 1996 and continuing through the first half of 2001 were analyzed for roadways with low to very low traffic volumes in ten southwestern Minnesota counties resulting in information about the causes of crashes. Three sets of analysis were carried out on the database. First was a descriptive analysis of the data to determine the general frequency rates of accidents. A second identified dangerous roadways. Counting the number of crashes on specific roadways and dividing this number by the average daily traffic (ADT) on a roadway generated crash rates for those roadways, including county state aid highways (CSAHs), county highways, and township roads. Roadways with the highest 5% were considered significantly dangerous. Crash rates were generated for specific locations. This method identified 15 dangerous locations, nine on CSAHs, three on county highways, and two on township roads. There were only 235 cases where no improper driving was indicated. The remaining 1,554 cases suggested that driver error was the major cause. The most likely factor in causing an accident on a highway with an ADT of less than 400 is a crash involving an animal. Road design factors such as number of lanes and the speed limit seem to be the factors related to these accidents.

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.