Work on a new type of intersection will alleviate an existing bottleneck at the intersection of Interstate 35 and RM 1431 (University Drive) in Round Rock. The Texas Department of Transportation, in cooperation with Williamson County and the City of Round Rock, has begun work on the area’s first-of-its-kind diverging diamond intersection (DDI).

The project is designed to enhance safety and reduce wait times and congestion by improving left-turn movements and replacing the traditional intersection currently in place. Other enhancements include adding a collector-distributor road, making ramp improvements and building additional sidewalks to accommodate pedestrians and bicyclists.

“This project will provide a huge relief to one of our fastest growing areas,” said Round Rock Mayor Alan McGraw. “We really appreciate all parties coming forward to find an innovative traffic solution for our citizens and businesses who are dependent on this intersection.”

A DDI is a new intersection design that addresses congestion by allowing vehicles to travel more quickly through an intersection. DDIs are particularly effective at locations that have a high volume of left-turn traffic. A DDI increases traffic flow by temporarily shifting traffic to the left side of the road, allowing through-traffic and left-turning traffic to proceed through the intersection simultaneously, which eliminates the need for left-turn arrows. The intersection design increases safety by reducing the number of potential conflict points between cross-traffic and left-turn movements.

Improvement benefits include:

• North and southbound traffic will have dedicated roads to bypass the intersection without stopping
• More “green time” at traffic lights will be available for east/west movements, and allow more vehicles to pass through the intersection in the same amount of time
• Reconstructed frontage roads and ramps will improve traffic flow into and out of the existing intersection

The project will cost an estimated $7 million and construction is expected to take about a year. The contractor is Capital Excavation Company of Austin.

“Diverging diamond intersections serve as relatively low cost improvements that will help address the rapidly-growing transportation demand in the area,” said Greg Malatek, Austin District Engineer. “This project will greatly enhance safety and mobility along the I-35 corridor.”