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Coordinating, Developing, and Delivering Highway Transportation Innovations

 
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Publication Number:  FHWA-HRT-13-083    Date:  July 2013
Publication Number: FHWA-HRT-13-083
Date: July 2013

 

FEDERAL HIGHWAY ADMINISTRATION OPERATIONS RESEARCH AND DEVELOPMENT
Saxton Transportation Operations Laboratory

Highway Capacity Manual (HCM) Methodology for Alternative Intersections / Interchanges

PDF Version (520 KB)

PDF files can be viewed with the Acrobat® Reader®

Project Objectives

Over the past decade, the Federal Highway Administration (FHWA) has conducted and developed extensive research, workshops, technical briefs, and other outreach materials about alternative intersections/interchanges.  These research efforts and publications have increased interest and rapid adoption of alternative geometric designs across the United States.  Of the many alternative intersection/interchange designs, stakeholders showed significant interest in these four:

  • Double Crossover Diamond (DCD) interchange (or Diverging Diamond Interchange (DDI)).
  • Displaced Left Turn (DLT) intersection.
  • Median U-Turn (MUT) intersection.
  • Restricted Crossing U-Turn (RCUT) intersection.

Most existing analysis tools supporting the adoption of alternative intersections/interchanges involve the use of complex microscopic simulations that are expensive and time consuming.  The Highway Capacity Manual (HCM) and the Highway Capacity Software (HCS) are widely used analytical tools that assess the quality of service for conventional intersections and interchanges. However, they do not assess any of the alternative designs considered in this project.

To support the increased exposure and interest in these designs, FHWA is conducting activities to integrate alternative intersection/interchange guidance into the HCM and HCS.  This will help expand the portfolio of design alternatives contained in the HCM and enable a side-by-side assessment of their operations in contrast to traditional designs.

 Artist’s rendering of a three-lane highway in which an offramp on the right allows traffice to diverge in advance of a skewed intersection.

 

The new HCM guidance and procedures resulting from this project will assist agencies in evaluating capacity and quality of service for the design and operation of alternative intersections/interchanges.

Pooled Fund Study
Partner States

Alabama, California,
Colorado, Florida,
Missouri, North
Carolina, Nevada, Ohio,
Washington, Wisconsin

DOT FHWA logo

Project Tasks

Flow chart describes the progression of each task in the FHWA project to integrate alternative intersection/interchange guidance into the HCM and HCS. Task 1, project management/coordination, is an overarching task covering all following task efforts. Task 2 involves reviewing the current HCM and proposing adaptations to current HCM methods. This task answers the question “exactly what?” Task 3 is to develop a data collection and analysis plan, which will answer the question “exactly how?” The results of tasks 1 and 2 will flow directly into tasks 4 through 7. Task 4 is to collect data, develop equations and procedures, dand validate equations and procedures. Task 4 both providing inputs to and deriving impacts from tasks 5 and 6 and results in “Execution.” Task 5 is to develop a computational engine and task 6 is to develop video files and outreach materials. All of these efforts will flow into task 7, prepare the final report.

The project consists of seven tasks.  Task 1 includes administrative activities throughout the duration of the project.  Task 2 involves identifying knowledge and methodology gaps in the current 2010 HCM, formulating an analysis framework, and identifying field data collection necessary to address knowledge and methodology gaps.  Task 3 will determine the applicability of existing HCM models to the new designs, and will decide whether data is on hand, or if field data collection and simulation are needed.  In Task 4, the project team will reduce and analyze field data collected for development of HCM procedures during Task 3 and prepare a report consisting of new or modified HCM procedures for each intersection/interchange type.  Task 5 will involve updating existing HCS modules to incorporate the newly developed methods for alternative intersections/interchanges. Tasks 6 and 7 will produce outreach videos from simulation and the final project report in the form of draft HCM chapters for alternative intersections/interchanges.
Aerial photograph of a restricted crossing U-turn intersection in which a minor road intersects a major six-lane road.
Artist’s rendering of a displaced left-turn intersection. In this rendition of a multi-lane intersection, traffic wishing to turn right from the through roadway diverges via a dedicated right lane lane to merge with cross-street traffic. Traffic wishing to turn left is relocated upstream of the first signal-controlled ramp terminal of the diamond interchange. This left-turning traffic is crossed over the opposing through lanes. This traffic then travels on a new roadway that is situated between the opposing through lanes and a roadway and that carries the right-turning traffic from the ramp.

Right-turning vehicles and rightlane merging with through traffic at a DLT intersection

Alternative Intersection/Interchange Designs Studied
Aerial photograph of a double crossover diamond interchange in which a highway is connected to an arterial cross street by two on-ramps and two off-ramps.

DCD interchange (also known as DDI)		 Aerial photograph of an median U-turn intersection in which direct left turns from the major approach have been eliminated. In order to turn left from the major road onto an intersecting cross-street, the driver must first pass the intersection and then make a U-turn at a downstream signalized median opening designed for that

MUT Intersection
Artist’s rendering of a couble crossover diamond or diverging diamond intersection. Here, a highway is connected to an arterial cross street by two on-ramps and two off-ramps. On the cross street, the traffic moves to the left side of the roadway between the ramp terminals. This allows the vehicles on the cross-street that need to turn left onto the ramps to continue to the on-ramps without conflicting with the opposing through traffic

Lane utilization at DCD interchange (also known as DDI) crossovers		 Aerial photograph of a displaced left-turn intersection in which traffic wishing to turn left from a divided highway onto a cross-street diverges via dedicated left turn lanes that cross opposing traffic in advance of the intersection, then merge into the cross-street traffic.

DLT Intersection		 Aerial photograph of a restricted crossing U-turn intersection in which a minor road intersects a major six-lane road. At the intersection, the through movements for the minor road are blocked by a median, although left-turn movements are allowed from the major road to the minor roads. Openings in the median are provided on either side of the intersection on the major road that allow vehicles to make a U-turn. In this configuration, the through traffic from the minor street must make a right turn into the main street, make a U-turn in the median, and take a right turn to continue on the minor road.

RCUT Intersection
Artist’s rendering of a restricted crossing U-turn intersection. In this design, two dedicated lanes enable a U-turn movement with a widened area of shoulder on the right shoulder of opposing traffic’s right lane to facilitate larger vehicles’ turning radius. The diagram highlights the queue length of the dedicated U-turn lanes

U-turn queue length at U-turn crossover for a Restricted Crossing U-Turn (RCUT) intersection

To Contribute to the Research Team’s Discussion

Inform – Provide effective marketing and outreach material that outlines progress on HCM guidance for alternative designs.

Educate – Provide working tools to State and local agencies and roadway practitioners for use on existing or new alternative design projects.

Interact – Generate effective outreach efforts to allow practitioners and researchers opportunities to interact and discuss issues and opportunities surrounding alternative designs.

Influence – Create opportunities for diverse groups to influence development of HCM guidance for and field deployments of alternative intersections/interchanges.

Collaborate – Provide a platform for collaboration among various groups with an interest in alternative designs.

Partner – Work with various agencies and individuals to enhance the value of HCM tools available to support the operations of and analysis needs for alternative designs.

The project team is maintaining an online collaboration tool to facilitate announcements, forums, and file sharing with project stakeholders, including the advisory and review groups. The research team intends to provide project updates and facilitate feedback in a variety of relevant forums.

 

Publication No.: FHWA-HRT-13-083
HRDO-20/07-13(200)E

 

For more information on the project, please contact:

Randy VanGorder, FHWA
202-493-3266
randall.vangorder@dot.gov

Joe Bared, FHWA
202-493-3314
joe.bared@dot.gov

July 2013

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