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RM 1431 Diverging Diamond Intersection

TxDOT is considering making intersection improvements to Ranch-to-Market (RM) 1431 (University Blvd) at I-35 in Round Rock.

Proposed Improvements

Proposed improvements include the following:

  • Replace the traditional intersection with a diverging diamond intersection (DDI)

A DDI is a new intersection design that can improve traffic flow and reduce congestion. It changes the normal four-phase signal operations to a more-efficient two-phase operation, which allows more flexibility addressing current and future traffic volumes.


Similar to the design of a conventional diamond intersection, the DDI differs in the way the left and through traffic navigates between the frontage roads. The purpose of this innovative design is to accommodate turning movements onto and from University Drive, while eliminating the need for a left-turn bay and signal phase at the signalized intersections.

Both north and southbound frontage road through traffic will be accommodated by collector-distributor roads along I-35. The northbound collector-distributor road is already in place and the southbound collector-distributor road is included as part of the proposed improvements. The preliminary estimates for the DDI intersection is just under $4 million. 

How Diverging Diamond Intersections Work

The highway is connected to the main cross street by on-ramps and off-ramps in a manner similar to a conventional diamond intersection. However, on the cross street, the traffic moves to the left side of the roadway between the frontage roads. This allows the vehicles on the cross street that need to turn left onto the ramps to continue to the on-ramps without conflicting with the opposing through traffic.


This innovative DDI design is particularly effective at locations that have high volumes of left-turn traffic. It works by reducing the number of vehicles that pass through the intersection and minimizing the number of potential conflicts between RM 1431 cross-traffic and left-turn movements. The benefits of a DDI include enhanced safety and more effective signal operation, which results in more “green time” for motorists.

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Contact Us

TxDOT Austin District
(512) 832-7000