I-37 Diverging Diamond Interchange (DDI)

I-37 from SL 13/SE Military Drive to I-410

Visualization showing how the I-37 DDI will look once constructed (preliminary, subject to change).

Overview

TxDOT is improving mobility in southeast San Antonio by bringing operational improvements to Interstate 37 (I-37) from Southeast (SE) Military Drive to I-410, including a diverging diamond interchange (DDI) at I-37/SE Military Drive. A DDI is an innovative design that moves traffic through the intersection more efficiently and safely than traditional intersections.

This nearly 2-mile project is a significant investment in transportation infrastructure designed to improve traffic operations, reduce travel times, alleviate congestion, and enhance mobility and safety throughout the project area.

Timeline: Late 2026 – 2029
Project length: Nearly 2 miles
Project cost: $40 million

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Project map

Project location map for I-37 from SL 13 (SE Military Drive) to I-410. Simple map. The project limits are shown beginning north of SL 13 and ending before I-410 to the south. The limits also cover SL 13 from Goliad Road to the next cross-street to the east of I-37. Other landmarks shown are Brooks Park to the west of I-37 and Salado Creek to the east of I-37. Copyright 2026 TxDOT San Antonio District.

Improvements

The following project elements are included:

Converting the I-37/SE Military Drive interchange to a DDI
Adding a bypass ramp above the DDI interchange:
Constructing a southbound I-37 frontage road with a transition into an auxiliary mainlane that would end at the exit ramp to I-410
Adding 10-foot-wide shared-use paths in both directions for bicyclists and pedestrians

No additional right-of-way (ROW) is required, and no displacements are anticipated.

What is a DDI?

A Diverging Diamond Interchange is an innovative intersection design that temporarily shifts crossroad traffic to the opposite side of the roadway through a series of crossovers. This design eliminates left‑turn conflicts with opposing traffic, reduces the number of locations where vehicles can cross paths, and enhances overall interchange safety and efficiency.

Learn more about DDIs on TxDOT’s dedicated DDI resource page, complete with graphics, videos, and FAQs.

Typical sections

I-37 Typical Sections

IH37 at SE Military Drive Typical Sections

Benefits

Once complete, the improvements are projected to:

Improve the flow of traffic, particularly at the I-37/SE Military Drive interchange.
Alleviate congestion
Improve mobility and enhance safety
Reduce travel times* on the following routes:
- I-37 between Pecan Valley and IH-410:
  - Northbound: 46 percent reduction
  - Southbound: 81 percent reduction
- I-37/SE Military Drive interchange via the I-37 southbound exit DDI: 90 percent reduction

* Compared against the “no build” condition if no improvements constructed by 2028.

Project timeline

What to expect during construction

While construction of the I-37 DDI project will require temporary lane closures, TxDOT is committed to construction schedules that minimize traffic impacts and allow work to be completed safely. To complete the project on schedule, work may occur during the day, at night, and on the weekends. However, to minimize disruption to the public, most lane closures will occur overnight (9 p.m. to 5 a.m.) during the week. TxDOT will notify the public of closures and access changes in advance.

Subscribe to our email list and follow us on social media for the latest construction information. You can also stay informed by visiting  www.DriveTexas.org  for the latest road conditions across the state.

More information on DDIs

A hallmark feature of TxDOT’s I-37 DDI project is the construction of a diverging diamond interchange (DDI). This innovative design moves traffic more efficiently and safely through the area.

A DDI is a type of innovative intersection design used by TxDOT to improve traffic flow, and enhance safety. The grade-separated, signalized DDI at I-37 temporarily moves crossroad traffic on SE Military Drive to the left side of the road through a series of crossovers within the interchange. This design eliminates left‑turn conflicts and makes it easier to access or exit from I-37. This shift also allows vehicles to make free-flowing left turns without crossing traffic, enhancing safety, mobility, access, and efficiency for all users.

The I-37 and SE Military Drive interchange is a heavily traveled area in southeast San Antonio. It is located within the Brooks Area Regional Center, which is an emerging activity center and a major catalyst for growth in the City of San Antonio. It is expected that traffic growth will continue in future years as the project area and its vicinity are redeveloped. A DDI helps address associated congestion and safety challenges.