Intersections

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.

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.

Six intersections were selected to monitor and record pedestrian and vehicle behaviors in slip lanes in Rochester, Minnesota, and potential countermeasures were evaluated for their effectiveness to convey the pedestrian presence information to the drivers, yet not interfering with the vehicle free-flow at other times.

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.

The authors present a vision-based method for monitoring crowded urban scenes in an outdoor environment: background detection, visual noise from weather, objects that move in different directions, and conditions that change from day to evening. Several systems of visual detection have been proposed previously. This system captures speed and direction as well as position, velocity, acceleration, or deceleration, bounding box, and shape features. It measures movement of pixels within a scene and uses mathematical calculations to identify groups of points with similar movement characteristics. It is not limited by assumptions about the shape or size of objects, but identifies objects based on similarity of pixel motion. Algorithms are used to determine direction of crowd movement, crowd density, and mostly used areas. The speed of the software in calculating these variables depends on the quality of detection set in the first stage. Illustrations include video stills with measurement areas marked on day, evening, and indoor video sequences. The authors foresee that this system could be used for intersection control, collection of traffic data, and crowd control.

This report summarizes the findings of a human factors analysis to determine the effects of advanced warning flashers (AWFs) on simulated driving performance. The Minnesota Department of Transportation sponsored the project. Researchers used the flat-screen simulator at the University of Minnesota Human Factors Research Laboratory to conduct experiments. They measured vehicle speed, braking, and acceleration/deceleration during simulated driving and visually observed stopping behavior. In addition, they analyzed responses to a post-test questionnaire. They created a 11.3-mile simulated driving environment with 10 signalized intersections and configured four experimental models: low speed limit (SL) of 50 miles per hour with no AWFs, low SL with AWF at each intersection, high SL of 65 miles per hour with no AWFs, and high SL with AWF at each intersection. Researchers set different vehicle-signal proximity intervals, with all green/ no yellow as the control, and zero seconds with the vehicle adjacent to the signal, two seconds, three-and-a-half seconds, or five seconds. With each model, they assigned two intersections each proximity interval, with the sequence of intersection proximity intervals ordered differently for each model. Each of 24 subjects completed duplicate driving trials with each model. The study revealed that, relative to intersections with no AWFs, drivers who encountered yellow signals at AWFs intersections: stopped more frequently at low SLs but not at high SLs, drove more slowly while approaching intersections with two and three-and-a-half second proximity intervals, and displayed less inconsistent behavior at intersections with short proximity intervals. Researchers concluded that AWFs assist drivers with decision-making behavior and promote safer driving behavior. They recommended field research to study and actual environment.

This report presents a real-time system for pedestrian tracking in sequences of grayscale images acquired by a stationary camera. Researchers also developed techniques for recognizing pedestrian's actions, such as running and walking, and integrated the system with a pedestrian control scheme at intersections. The proposed approach can be used to detect and track humans in a variety of applications. Furthermore, the proposed schemes also can be employed for the detection of several diverse traffic objects of interest, such as vehicles or bicycles. The system outputs the spatio-temporal coordinates of each pedestrian during the period the pedestrian is in the scene. The system processes at three levels: raw images, blobs and pedestrians. Experimental results based on indoor and outdoor scenes demonstrated the system's robustness under many difficult situations, such as partial or full occlusions of pedestrians. In particular, this report contains the results from a field test of the system conducted in November 1999.

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.