Diverging diamond interchange (DDI) at Blanco Road
Loop 1604 North Expansion
The Loop 1604 North Expansion is bringing major improvements to one of the corridor's busiest intersections: Loop 1604 and Blanco Road. As part of this work, the Texas Department of Transportation (TxDOT) is opening a diverging diamond interchange (DDI) - an innovative design that moves traffic more efficiently and safely through the area.
This page explains what a DDI is, why it is being built, when it will open, and how to navigate the new intersection.
What is a diverging diamond interchange (DDI)?
A DDI is an innovative intersection design that shifts traffic to the left side of the roadway as drivers travel on Blanco Road through the interchange. This shift allows vehicles to make free-flowing left turns without crossing opposing traffic.
Why a DDI at Blanco Road?
The Loop 1604 and Blanco Road intersection is one of the most heavily traveled areas in north San Antonio. A DDI helps address congestion and safety challenges.
Benefits of the DDI
DDI makes things easier.
Free-flow left turns create smoother movements through the intersection.
DDI gets you moving faster.
Shorter signal cycles mean less time waiting at red lights.
DDI makes travel safer.
Fewer conflict points reduce the potential for crashes.
Timeline
March 2026
Traffic shifts to DDI conditions.
Spring 2026
Major roadway and bridge work complete.
Summer 2026
Final phase of construction.
Late summer 2026
The DDI is complete.
Traffic switch to DDI conditions
In March 2026, drivers will experience a traffic switch to DDI conditions as crews move into the final phase of construction.
What to expect during the final phase of construction
- Traffic on Blanco Road will shift to the left when crossing Loop 1604.
- Through traffic on Loop 1604 frontage roads must use the bypass ramps.
- Temporary traffic signals will be in operation.
- Barriers will be installed to allow for the construction of concerete islands.
- Pedestrian access may be limited.
- Weeknight closures will continue.
Tips for driving through the work zone
- Reduce driving speed through the work zone.
- Follow posted signs and message boards.
- Stay alert for changes in traffic patterns.
- Allow extra travel time.
- Watch for workers and obey reduced speed limits.
How to drive the DDI
It may look different at first, but DDIs are simple to drive and are proven to reduce crashes and improve traffic flow.
Drivers on NB Blanco Road will use the following lanes based on their destination:
• Left lane: WB Loop 1604
• Right/middle lanes: Through traffic
• Right turn lane: EB Loop 1604
Drivers on SB Blanco Road will use the following lanes based on their destination:
• Left lane: EB Loop 1604
• Right/middle lanes: Through traffic
• Right turn lane: WB Loop 1604
Drivers on EB and WB Loop 1604 frontage road may bypass the Blanco Road intersection:
• Keep left on the frontage road approaching Blanco Road
• Enter the bypass lane, traveling under Blanco Road
• Re-enter the frontage road or mainlanes at the end
Drivers on EB Loop 1604 will use the following lanes based on their destination:
• Right turn lane: SB Blanco Road
• Left lane: U-turn to WB Loop 1604
• Middle lanes: NB Blanco Road
Drivers on WB Loop 1604 will use the following lanes based on their destination:
• Right turn lane: NB Blanco Road
• Left lane: U-turn to EB Loop 1604
• Middle lanes: SB Blanco Road
DDI resources
Frequently asked questions
A DDI is an intersection design that briefly shifts traffic to the left side of the road as vehicles cross a highway. This allows drivers to make left turns without waiting for a dedicated left turn signal, improving traffic flow, and reducing congestion.
This intersection experiences heavy traffic volumes and significant left-turn demand. A DDI improves mobility, reduces delays, and enhances safety by simplifying turning movements and reducing conflict points.
A conflict point is a location in an intersection where two vehicle paths can cross, merge, or diverge. These points represent places where crashes are most likely to occur.
A traditional intersection has 26 conflict points. A DDI has 14 conflict points. DDIs help lower the risk of crashes and improves overall safety.
National studies show that DDIs can reduce crash rates by up to 60 percent. The design reduces the number of places where vehicles can cross paths, which lowers the likelihood of serious crashes.
Drivers shift to the left side of the roadway at a signalized crossover. Once on the left, vehicles can continue straight or make a left turn without stopping for a separate signal phase. Traffic then shifts back to the right side after crossing the interchange.
Most drivers adjust quickly. The roadway is designed with clear signs, pavement markings, and traffic signals that guide vehicles through the interchange.
DDIs are already operating successfully across the country. TxDOT has seven DDIs in operation near the areas of Austin, College Station, Dallas and El Paso.
During the transition to the final DDI configuration, drivers may see:
- A shift to the left side of Blanco Road when crossing Loop 1604
- Required use of bypass ramps for through-traffic on the frontage roads
- Temporary traffic signals
- Barriers for concrete island construction
- Limited pedestrian access
- Continued weeknight closures
Pedestrian access may be limited during construction. Once complete, the DDI will include designated pathways and crossings for pedestrians and cyclists.
The final phase of construction on the DDI is expected to be complete in late summer 2026.
Emergency vehicles will move through the DDI the same way they do at traditional intersections. The design accommodates large vehicles, including fire trucks and ambulances.