Potential MUTCD Criteria for Selecting the Type of Control for Unsignalized Intersections (2015)

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1 SUMMARY INTRODUCTION The 2009 Manual on Uniform Traffic Control Devices (MUTCD) includes guidance for the use of various types of traffic control at unsignalized intersections. Despite changes and advances in traffic engineering in recent decades, the MUTCD content related to selection of traffic control in Part 2B has seen only minor changes since 1971. The values for volumes and crashes contained within Sections 2B.04, 2B.06, 2B.07, and 2B.09 of the 2009 edition of the MUTCD have not been evaluated based on research since that time. Research was desired to examine the warrants (criteria) in Part 2B for determining whether an intersection should have no control, yield control, or stop control. This National Cooperative Highway Research Program project was tasked with developing criteria and supporting material for determining appropriate traffic control at unsignalized intersections. The types of unsignalized traffic control to be addressed included no control, yield control, two-way stop control, and all-way stop control. The material produced was to be suitable for integration into an update to the 2009 MUTCD Sections 2B.04 through 2B.09. Within the context of this research, an unsignalized intersection is one where one of the following methods of right-of-way control is used on one or more of the approaches:  No control: Right of way is based on the rules of the road where the first to arrive at the intersection has the right of way, and if two vehicles arrive at the same time, a driver yields to the vehicle to the right.  Yield control: YIELD sign(s) are installed on the minor approach or approaches. At a roundabout intersection, YIELD signs are installed on all approaches.  Minor-road stop control: STOP sign(s) are installed on one approach for a three-leg intersection or on two approaches for a four-leg intersection. The STOP sign is normally installed on the minor road but in some cases may be installed on the major road with no control on the minor road.  All-way stop control: STOP signs are installed on all approaches to the intersection. The next level of right-of-way control for an intersection is a traffic control signal, criteria for which were not included in the scope of this research. RESEARCH ACTIVITIES Review of Policies and Guidelines Researchers reviewed the current MUTCD and the supporting material for the guidance found therein. The research team also conducted searches of guidelines and manuals from all 50 states (available online) to review their current policies. In addition, researchers asked practitioners for information on novel approaches they were considering for selecting traffic control at unsignalized intersections. Several states provide guidance in addition to that found in the MUTCD, but in many jurisdictions, the MUTCD (or a particular state’s equivalent) is the

2 prevailing source for guidance. Much of the existing text in the MUTCD has remained largely intact for several decades. Literature Review The research team had a three-pronged approach to reviewing the relevant literature: key reference documents, previous literature that discussed methods for selecting traffic control at unsignalized intersections, and previous literature that discussed methods for selecting traffic control at unsignalized pedestrian crossings. Key reference documents included the Highway Capacity Manual, Highway Safety Manual, and the Institute of Transportation Engineers’ Manual of Traffic Engineering Studies. Literature that described the selection of traffic control included processes that considered delay, traffic volumes, number of lanes, crashes, and other variables. Some processes resulted in regression equations or charts to calculate the variables of interest, while others were based on a point system that described a recommended traffic control for a certain point score. Critical Review of MUTCD Researchers reviewed key sections of MUTCD Chapter 2B to determine which sections could have the most potential benefit from new research to support revised guidance. Based on the activities in the initial phase of the project, the research team, with the guidance of the project panel, conducted a study in the second phase of the project that focused on the following items:  Set a higher priority on investigating when to go from two-way to all-way stop control rather than when to go from no control to yield or two-way stop control.  Develop criteria that reflect urban and rural environments or speed conditions.  Develop criteria that are sensitive to the number of legs at the intersection.  Consider roundabouts as a geometric design alternative within the evaluation.  Consider a variety of major- and minor-road volume splits and not just when the split is “approximately equal.”  Consider the existing and ongoing revisions to relevant sections of the MUTCD, such as the changes suggested for the reorganization. Economic Analysis Procedure The research team used a procedure for comparing traffic control alternatives based on the relative economic costs and benefits of those alternatives for particular intersection types (three- leg or four-leg), environments (urban or rural), and volumes (varying levels of major- and minor- road volumes). Based on information from a variety of relevant sources, the research team selected user delay, crashes, vehicle operating, and construction as the four costs for consideration in the project. Researchers used microsimulation to measure the effects of delay. A multi-step process for calculating crash costs was adapted from the Highway Safety Manual. Vehicle operating costs were estimated using information from federal sources such as the Environmental Protection Agency and the Energy Information Administration. Roundabout construction costs were estimated from information from the Federal Highway Administration.

3 Potential Criteria Potential criteria for no control, yield control, minor-road stop control, and all-way stop control were identified from the literature, reviews of policies and guidelines, and the economic analysis. RECOMMENDATIONS Use of Findings from Economic Analysis A portion of the research efforts focused on an economic analysis to determine when all-way stop control or roundabout geometric design should be considered based on cost considerations. The research team members do not support implementation of these findings at this time for several reasons as discussed in this report. While the findings from the economic analysis are based on thorough research, the research team identified some important inconsistencies between the methodologies used for the current MUTCD signal criteria and those used for the potential all-way stop-control criteria developed in this research. The differences in basis between these criteria and those that are currently in the MUTCD mean that the criteria developed from the economic analysis may not be ready for inclusion in the MUTCD until such time as the existing MUTCD criteria and warrants for traffic signals can also be reevaluated in a manner that considers the impacts of user safety costs in the same manner that this research project did. Only through the use of consistent decision-making criteria can practitioners correctly determine the most appropriate means of providing right-of-way control at an intersection. Recommended Language for Next Edition of the MUTCD Using information available from reviews of existing literature, policies, guidelines, and findings from the economic analysis, along with the engineering judgment of the research team and panel, recommendations were developed. The language proposed for the next edition of the MUTCD for unsignalized intersections developed at the conclusion of this research is provided in the appendix. The proposed language includes introductory general considerations, discusses alternatives to changing right-of-way control, and steps through the various forms of unsignalized control from least restrictive to most restrictive, beginning with no control and concluding with all-way stop control. Supplemental notes are provided to suggested additions to the current text, which show the reader the source(s) of the material and/or the research team’s reasoning for proposing the text.