I-64 Interchange at Route 15, Zion CrossroadsConstruction of diverging diamond interchange (DDI)
Est Completion Date
Opened to traffic Feb. 21, 2014; completed April 15, 2014
$6.883 million design-build contract
Lengths and Limits
Design: Parsons Corporation / Construction: Corman Construction Inc.
The Virginia Department of Transportation (VDOT) completed construction on the Zion Crossroads diverging diamond interchange (DDI) on April 15, 2014, finishing on time and under budget.
When driving the new DDI , motorists will proceed through a traffic signal at the interchange and follow their lane to the opposite side of the roadway.
Vehicles needing to access Interstate 64 will merge left using an on-ramp without having to stop or wait for oncoming traffic to pass.
Through traffic proceeds to a second traffic signal and follows their lane back to the right side of the road.
The purpose of this project was to improve the I-64 interchange on Route 15 at Zion Crossroads (exit 136).
In 2007, VDOT identified a need to increase the capacity of the I-64 off-ramps at the Route 15 interchange, which — combined with a forecasted increase of traffic due to the area’s commercial growth — prompted a study of potential interchange options.
In addition to the DDI, VDOT analyzed the construction of a single-point urban interchange, improvements to the existing diamond interchange, and a no-build alternative.
The clover-leaf interchange was not included based on the amount of land acquisition it would require.
Overall, the diverging diamond interchange produced the best results based on current traffic volumes as well as those projected for 2035.
VDOT reconstructed the 0.49-mile stretch where Route 15 meets I-64 (exit 136) as a DDI.
By shifting vehicles to the opposite side of the road, this design eliminates traditional left turns that cross over oncoming traffic.
The DDI improves safety by reducing the number of spots where vehicles could collide and can handle more than 600 left-turn movements per hour, twice the capacity of a conventional interchange.
This was the first diverging diamond interchange in Virginia. Others:
- Interstate 581 and Valley View interchange improvements, Roanoke
- I-66 and Route 15 interchange reconstruction, Haymarket
- Southgate Connector at Virginia Tech, Blacksburg
The diverging diamond interchange is new to the U.S. Though the design originally appeared in the 1970s in Versailles, France, America’s first DDI was built in 2009 in Springfield, Missouri.
There are now approximately 30 DDIs in operation nationwide.
Flier on DDI operation and background:
8.5 by 11 inches, one-sided (142 KB)
8.5 by 5.5 inches, two-sided, prints two per sheet (149 KB)
YouTube video simulation of interchange design
Diagram of interchange design (321 KB)
- 2016 Outstanding Owner Award, Design-Build Institute of America, Mid-Atlantic Region
- 2015 National Award of Merit, Design-Build Institute of America (awarded to Corman Construction Inc.)
- 2015 Award of Merit, Design-Build Institute of America, Mid-Atlantic Region (awarded to Corman Construction Inc.)
- 2014-2015 Engineering Excellence Honor Award, American Council of Engineering Companies of Metropolitan Washington