MoPac Diverging Diamond Interchange – Texas Department of Transportation

Austin Texas

The Texas Department of Transportation (TxDOT) selected planning, engineering and program management firm Lockwood, Andrews & Newnam, Inc. (LAN) as lead designer for MoPac Expressway improvements at Slaughter Lane in southwest Austin. The project includes the first Diverging Diamond Interchange (DDI) in the city.

DDIs are designed to move large volumes of left-turn traffic through intersections by reducing the number of traffic signal intervals, thereby reducing wait time for traffic making a left turn. The improvements will include retaining walls at the bridges, a storm sewer system, traffic signals and new pavement, striping and signing throughout the project limits. The MoPac/ Slaughter DDI will be illuminated and traffic signals will be interconnected with other Slaughter signals nearby to move traffic efficiently. TxDOT and the City of Austin are working together to provide connectivity on a local hike and bike shared use path. Additionally, the DDI will provide bike lanes and ADA compatible pedestrian facilities.

To protect the environmentally sensitive Edwards Aquifer Recharge Zone, the project team will incorporate both temporary and permanent erosion control and water quality measures into the design. During construction, sediment control fencing, construction exits, rock filter dams, inlet filters and other methods will be incorporated. Once constructed, the project will include permanent water quality features such as water quality basins, hazardous material traps and permanent vegetative filter strips.

At a glance

650 cars per lane per hour turning left: traffic throughput for a DDI

325 cars per lane per hour turning left: traffic throughput for a diamond intersection

First DDI LAN has designed


First DDI in City of Austin

Intelligent traffic systems

Ten foot shared use path for bicycles & pedestrians

Overhead guide signs

Water quality ponds

Detention ponds

Hazardous materials traps



Planning & Modeling

Transportation Services


Texas Department of Transportation

Related Work

Planning and Modeling



Transportation Services