Michigan Department of Transportation Diverging Diamond Interchange (DDI) Informational Guide April 2015 Engineering Manual Preamble This manual provides guidance to administrative, engineering, and technical staff. Engineering practice requires that professionals use a combination of technical skills and judgment in decision making. Engineering judgment is necessary to allow decisions to account for unique site-specific conditions and considerations to provide high quality products, within budget, and to protect the public health, safety, and welfare. This manual provides the general operational guidelines; however, it is understood that adaptation, adjustments, and deviations are sometimes necessary. Innovation is a key foundational element to advance the state of engineering practice and develop more effective and efficient engineering solutions and materials. As such, it is essential that our engineering manuals provide a vehicle to promote, pilot, or implement technologies or practices that provide efficiencies and quality products, while maintaining the safety, health, and welfare of the public. It is expected when making significant or impactful deviations from the technical information from these guidance materials, that reasonable consultations with experts, technical committees, and/or policy setting bodies occur prior to actions within the timeframes allowed. It is also expected that these consultations will eliminate any potential conflicts of interest, perceived or otherwise. MDOT Leadership is committed to a culture of innovation to optimize engineering solutions. The National Society of Professional Engineers Code of Ethics for Engineering is founded on six fundamental canons. Those canons are provided below. Engineers, in the fulfillment of their professional duties, shall: 1. Hold paramount the safety, health, and welfare of the public. 2. Perform Services only in areas of their competence. 3. Issue public statement only in an objective and truthful manner. 4. Act for each employer or client as faithful agents or trustees. 5. Avoid deceptive acts. 6. Conduct themselves honorably, reasonably, ethically and lawfully so as to enhance the honor, reputation, and usefulness of the profession. This page is intentionally blank. FOREWORD The Federal Highway Administration (FHWA) Every Day Counts (EDC) initiative is designed to identify and deploy innovation aimed at reducing project delivery time, enhancing safety and protecting the environment. In 2012, FHWA chose Intersection & Interchange Geometrics (IIG) to feature as one of the innovative technologies in EDC-2. Specifically, IIG consists of a family of alternative intersection designs that improve intersection safety while also reducing delay, and at lower cost and with fewer impacts than comparable traditional solutions. As part of the effort to mainstream these intersections, FHWA has produced a series of guides to help transportation professionals routinely consider and implement these designs. Concurrent with a Diverging Diamond Interchange (DDI) Informational Guide, FHWA developed and published guides for three other designs: Median U-turn (MUT), Displaced Left Turn (DLT), and Restricted Crossing U-turn (RCUT). These guides represent summaries of the current state of knowledge and practice, and are intended to inform project planning, scoping, design and implementation decisions. An electronic version of the FHWA DDI document is available on the Office of Safety website at http://safety.fhwa.dot.gov/. Additionally, limited quantities of hard copies are available from the Report Center; inquiries may be directed to [email protected] or 814-239-1160. In response to the growing interest in DDIs, the Michigan Department of Transportation has developed this DDI Informational Guide based on the August 2014 FHWA version. The Michigan guide will serve as the basis of future DDI design in the state of Michigan. Michigan Department of Transportation Diverging Diamond Interchange Informational Guide i DDI INFORMATIONAL GUIDE TABLE OF CONTENTS CHAPTER 1 INTRODUCTION ..................................................................................................1 Overview of Alternative Intersections and Interchanges .................................................................1 Intersection Control Evaluations and Considerations .....................................................................1 Organization of the Guidelines ........................................................................................................2 Scope of the Guide .........................................................................................................................3 DDI Overview ..................................................................................................................................3 Application ......................................................................................................................................4 Geometric Design Considerations ................................................................................................10 Resource Documents ...................................................................................................................12 CHAPTER 2 POLICY AND PLANNING ................................................................................14 Planning Considerations for Alternative Intersections and Interchanges ......................................14 Serving Pedestrians and Bicycles ................................................................................................14 Traffic Volume Relationships .........................................................................................................15 Stakeholder Outreach ...................................................................................................................16 Policy Considerations ...................................................................................................................20 Asset Management .......................................................................................................................20 Planning Considerations ...............................................................................................................21 Planning Challenges .....................................................................................................................22 Project Performance Considerations ............................................................................................23 Project Development Process ......................................................................................................24 Summary of DDI Advantages and Disadvantages ........................................................................24 CHAPTER 3 MULTIMODAL CONSIDERATIONS...............................................................26 Design Principles and Approach ..................................................................................................27 Pedestrians ...................................................................................................................................30 Bicyclists .......................................................................................................................................45 Transit ...........................................................................................................................................49 Heavy Vehicle Considerations ......................................................................................................51 CHAPTER 4 SAFETY ................................................................................................................52 Safety Principles ...........................................................................................................................52 General Safety Concerns ..............................................................................................................54 Observed Safety Performance .....................................................................................................57 Incident Response Considerations ...............................................................................................63 Safety Evaluation Considerations .................................................................................................63 Michigan Department of Transportation ii Diverging Diamond Interchange Informational Guide DDI INFORMATIONAL GUIDE TABLE OF CONTENTS CHAPTER 5 OPERATIONAL CHARACTERISTICS ...........................................................64 Introduction ...................................................................................................................................64 Operational Considerations ..........................................................................................................68 Signal Timing and Coordination ....................................................................................................76 Comparative Performance Studies ...............................................................................................83 CHAPTER 6 OPERATIONAL ANALYSIS ..............................................................................85 Operational Analysis Tool Overview..............................................................................................86 Planning-Level Analysis ................................................................................................................86