Crashes at rural unsignalized intersections are a significant cause of fatal and injury crashes. Minnesota counties and the Minnesota Department of Transportation have implemented and evaluated several safety strategies including the technology-based methods detailed in this report. Safety improvements range from low-cost sight triangle improvements to high cost roadway geometric changes. In addition to these traditional methods, the use of Intersection Conflict Warning Systems (ICWS) and flashing LED STOP signs have proven effective in reducing severe crashes. ICWS warn drivers of other traffic approaching the intersection. The goal is that increased awareness may improve split-second decision-making that occurs when a traffic conflict is recognized. Because the ICWS are deployed at targeted locations, drivers that see the active alert may drive more defensively. It is not expected that drivers will slow down significantly or drastically change their behavior, but this awareness can make a small change that can translate into a big impact in reducing the severity of crashes from fatal to injury or from injury to property damage only or to no crash at all. Most of these crashes are caused by a failure to yield by a minor road vehicle that is entering the intersection. The driver on the minor road misjudges the gap, enters the intersection, and is struck by a major road driver. ICWS with warnings for the minor road may assist drivers with gap rejection to more safely navigate the intersection. This report also explains the use and effect of flashing LED STOP signs. In general, these signs have a similar effect to STOP signs with beacons. These signs are effective in reducing how often drivers run the STOP sign. Crashes of this nature are less common than those due to misjudging gaps, but can be just as severe. LED STOP signs are visible to drivers from farther away and some drivers reduce their speed when approaching the intersection. Like ICWS, LED STOP signs can be dynamically activated by cross traffic or based on speed profiles of the vehicle approaching the intersection. Both of these methods may increase the awareness because drivers become less acclimated to the flashers and see the alert only when it is most needed. This guidebook explains several options for ICWS deployment and gives expected costs to plan, deploy, and maintain ICWS and LED stop signs. Deployment costs for ICWS range from $50,000 to $125,000 and deployment costs for LED STOP signs start at about $2,000 per sign and increase if additional detection and communication components are added. Finally, this guidebook has a series of appendices that offer resources that may be useful for Minnesota local agencies that are considering implementing these systems. Of particular note, eight case studies are presented that explain successes and lessons learned from installing these systems. Example plans for three specific ICWS projects are also included as a reference for future design. The purpose of this Guidebook is to supplement MnDOT’s Traffic Engineering Manual (TEM) and Traffic Safety Fundamentals Handbook with recent improvements to address traffic safety at rural 2-way STOP controlled intersections. These recent improvements are LED STOP signs and Intersection Conflict Warning Systems (ICWS) and examples of these signs are shown in Figure 1. These safety strategies should be included for consideration along with traditional strategies such as improving visibility of the intersection with improved signing, pavement marking, and intersection lighting; improving sight distance by providing clear sight triangles on all approaches; selecting appropriate traffic control such as ALL WAY STOP; and reduce conflict points through geometric design such as turn lanes or bypass lanes. This Guidebook contains information that should be useful to the Engineer as they consider alternative solutions to traffic safety concerns at STOP controlled intersections. It is the intent of this guide to provide the engineer information to aid in the consideration, selection and deployment of LED STOP signs and ICWS at these intersections. Other safety improvements are detailed in the TEM and Traffic Safety Fundamentals Handbook. The systems shown as ICWS systems have varying designs including major road warning, minor road warning, and combined major and minor road warning. Example layouts of these systems are described later in this guidebook. (Author/publisher)
Samenvatting