U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
Jeffrey Shaw
jeffrey.shaw@dot.gov
"Also Known As…"
Diverging Diamond Interchange is sometimes called:
Displaced Left Turn Intersection is sometimes called:
Outreach & Education
Technical Materials
Other Resources
State & Federal Research
National Partners
Motorists, pedestrians, and bicyclists face greater mobility challenges and safety risks at intersections as traffic volumes grow and congestion worsens. Agencies need safer, more balanced designs that keep people moving. Innovative intersection designs offer many safety and operational benefits, and are being built more often because they can deliver more for less. In the case of Crossover-based intersection designs, some or all traffic crosses over to the left-hand side of the roadway in order to facilitate unopposed left turn movements. The two most common forms of innovative intersection designs that rely on crossovers are the Diverging Diamond Interchange (DDI) and the Displaced Left Turn intersection (DLT). The diagrams below illustrates these two designs – the DDI (on the left) and the DLT (on the right).
The success of innovative intersection designs begins with reducing the number and severity of conflict points – locations where user paths coincide. Conflict points are categorized as crossing, merging (or joining) and diverging (or separating). The diagrams below illustrate the differences in conflict points between conventional designs and equivalent DDI and DLT designs. For the DDI, there are 14 conflict points (2 crossing, 6 merging and 6 diverging), compared to 26 conflict points (10 crossing, 8 merging and 8 diverging) for a conventional diamond design. For the DLT, there are 28 conflict points (12 crossing, 8 merging and 8 diverging), compared to 32 conflict points for a conventional intersection (16 crossing, 8 merging and 8 diverging). In both cases, total conflict points are reduced, and the conflicts that remain are lesser overall severity – mostly the same-direction types with less likelihood of severe injury.
| Vehicle-Vehicle Conflict Points |
Conventional Diamond Interchange |
Diverging Diamond Interchange |
|---|---|---|
 |
 |
 |
| Crossing | 10 | 2 |
| Merging | 8 | 6 |
| Diverging | 8 | 6 |
| Total | 26 | 14 |
| Vehicle-Vehicle Conflict Points |
Conventional Intersection |
Displaced Left Turn Intersection |
|---|---|---|
|
 |
 |
| Crossing | 16 | 12 |
| Merging | 8 | 8 |
| Diverging | 8 | 8 |
| Total | 32 | 28 |
Because innovative intersections generally look or function differently from conventional designs, it is important for outreach and education to take place. These conversations begin by communicating the magnitude and importance of the intersection safety challenge. With roughly ¼ of all traffic fatalities in the United States associated with intersections, it is critical that safer designs are implemented as widely and routinely as possible. But safer designs must also keep people and goods moving. To help state and local road agencies advance innovative intersection designs, the FHWA produces materials intended to communicate their advantages and benefits to a variety of different audiences. These resources are conveniently listed and linked below:
Information Videos Informational Brochures Informational Case Studies Public Roads Magazine ArticlesDiverging Diamond Interchange Informational Guide (FHWA, 2014) [PDF]
Displaced Left Turn Intersection Informational Guide (FHWA, 2014) [PDF]
Double Crossover Diamond Interchange Tech Brief (FHWA, 2009) [HTML] [PDF]
Displaced Left Turn Intersection Tech Brief (FHWA, 2009) [HTML] [PDF]
Displaced Left Turn Interchange Tech Brief (FHWA, 2009) [HTML] [PDF]
Alternative Intersections/Interchanges Informational Report (FHWA, 2010) [HTML] [PDF]
Innovative Intersections – DDI Informational Guide Webinar [Recording]
Innovative Intersections – DLT/MUT/RCUT Informational Guides Webinar [Recording]
National Highway Institute Course #380109 "Alternative Intersections & Interchanges" [HTML] [PDF]
Capacity Analysis for Planning of Junctions (CAP-X) Tool [HTML]
Every Day Counts 2 – Intersection & Interchange Geometrics Initiative Resources
Transportation Research Board Alternative Intersection/Interchange Symposium Proceedings (via TeachAmerica) [HTML]
State Highway Agency Resources: Safety Evaluation of Diverging Diamond Interchanges in Missouri (Missouri, 2015) [PDF]
Diverging Diamond Interchange Observations and Experience (Utah, 2012) [PDF]
Diverging Diamond Interchange Performance Evaluation (I-44 & Route 13) (Missouri, 2011) [PDF]
Improving Intersection Design Practices (Kentucky, 2011) [PDF]
An Integrated Computer System for Analysis, Selection and Evaluation of Unconventional Intersections (Maryland, 2011) [PDF]
Missouri's Experience with a Diverging Diamond Interchange – Lessons Learned (Missouri, 2010) [PDF]
Evaluation of Sign and Marking Alternatives for Displaced Left Turn Lane Intersections (FHWA, 2009) [HTML] [PDF]
Drivers' Evaluation of the Diverging Diamond Interchange Tech Brief (FHWA, 2008) [HTML] [PDF]
Safety and Operational Impacts of Alternative Intersections (Indiana, 2008) [PDF]
Continuous Flow Intersection Report – US 61 (Airline Highway) @ LA 3246 (Siegen Lane) (Louisiana, 2007) [PDF]
Transportation Research Board Roundabouts Subcommittee (AHB65(1)) Home Page [HTML]
