As Segment 3 of the Loop 1604 North Expansion project reaches its final phases, the Texas Department of Transportation is beginning construction on San Antonio’s first diverging diamond interchange at the Blanco Road and Loop 1604 interchange.
This new configuration is designed to ease traffic congestion at one of the most heavily traveled corridors in the region.
The overview
Jennifer Serold, public information officer for the TxDOT’s San Antonio district, said the new Blanco Road and Loop 1604 diverging diamond interchange, or DDI, will temporarily shift traffic to the left side of the road, allowing free‑flow left turns, shorter signal cycles, and safer, more efficient movement through one of the region’s busiest intersections.
“[The DDI] can move up to double the number of vehicles through the intersection when compared to a traditional one, and it makes travel safer by reducing the potential for crashes,” Serold said.
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 lanes.Temporary traffic signals will be in operation.Barriers will be installed to allow for the construction of concrete islands.Pedestrian access will be limited.Week night closures will happen as needed.
The Blanco Road and Loop 1604 interchange is the eighth Diverging Diamond Interchange in Texas. (Courtesy Texas Department of Transportation)Serold said that there are hundreds of DDIs throughout the country, and are frequently seen in Kansas, Missouri and Utah. The Blanco and Loop 1604 interchange DDI was modeled after an interchange in Springfield, Missouri. Currently, there are seven DDIs throughout Texas in Austin, College Station and El Paso.
DDI benefits:
Allows for continuous left-turn movements without a separate signal phaseReduces the number of conflict points where crashes can occurImproves traffic flow during peak travel timesEnhances mobility along one of the region’s most heavily traveled corridorsTraffic delays decrease by roughly 60%Fatal and injury crashes decrease by roughly 60%Left-turn crashes decrease from 31% to 4% of total crashesNo-injury crashes decrease from 68% to 58% of total crashesThe interchange will eliminate the need for separate left-turn signals, it will have shorter signal cycles and fewer signal phases, and will include dedicated bike lanes and pedestrian crossings.
Looking ahead
A full weekend closure to shift traffic to the DDI pattern is anticipated to occur in March, with Serold stating that the shift will not occur over March 13 so as not to interfere with spring break. TxDOT officials said the speed limit will be reduced to 35 mph during construction but will be raised back to the normal 45 mph once construction is complete.
Intersection construction timeline:
March 2026: traffic shifts to DDI conditionsSpring 2026: major roadway and bridge work completeSummer 2026: final phase of constructionLate summer 2026: DDI is complete
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