By Robert D. Austin, Contributing Author
In 2020, the Texas Department of Transportation (TxDOT) completed construction of the Missouri Pacific Railroad (MoPac) Expressway intersections at Slaughter Lane and La Crosse Avenue in Austin.
MoPac and Slaughter Lane was reconfigured with a diverging diamond intersection (DDI). Two miles down the road, MoPac and La Crosse was rehabilitated with a grade separation.
This marked a milestone for the state's transportation infrastructure.
Part of State Highway Loop 1, the intersections exemplify modern engineering's capability to enhance the safety of motorists and cyclists, while also considering accessibility for people with disabilities.
There was a 43% reduction in crashes over a three-year period after the intersections opened to traffic, according to TxDOT’s crash records information system.
The project underscores the importance of strategic infrastructure improvements.
The safety benefits of the MoPac Expressway Intersections Project are undeniable. Before its construction, the area was notorious for traffic delays and frequent crashes, which caused increasing concern among residents and commuters.
The redesign started in 2013 with an environmental study conducted by the Central Texas Regional Mobility Authority and TxDOT. The study’s build alternative extended the MoPac main lanes under Slaughter Lane and La Crosse Avenue.
Lockwood, Andrews and Newnam, Inc. (LAN) was chosen as the lead design engineer.
The intersections now boast advanced traffic signal equipment that enhance the flow of traffic, reducing the potential for collisions.
At MoPac and Slaughter Lane, the DDI has minimized the conflicting movements and erratic driving behaviors that can come from traffic congestion.
As the first DDI in Austin and the second in the Austin region, the project marked a new time for innovative interchanges for area motorists, cyclists and pedestrians.
As a Professional Engineer and project director at LAN, I can attest that safety was paramount when the project was designed and executed. Reducing the wait times from several traffic signal cycles down to one in peak hours eliminated a lot of start-stops and rear-end crashes.
The DDI has reduced the potential for conflicting crossing movements and merging movements, which has enhanced safety at the interchange.
Navigating Challenges
The construction of the MoPac Expressway Intersections was challenging. One of the obstacles was the presence of underground caves. These geological formations required careful planning and innovative engineering solutions to ensure the stability and safety of the new infrastructure.
Building on top of limestone subgrade known to have caves was an issue we had to thoroughly investigate and work through with TxDOT.
LAN developed plans and specifications for the project. This included TxDOT’s standards to handle voids of different sizes.
Significant voids were encountered at the La Crosse Avenue Bridge, and the TxDOT Bridge Division provided additional structural details for substructure design.
The project also delivered environmental benefits. Before the redesign, long lines of idling cars were a common sight. These emissions degrade the air quality.
The redesigned intersections effectively alleviated this issue. It had been ranked as one of Texas’ 100 most congested intersections by a study conducted by the organization MoPac South, but vehicles now spend less time idling.
Batch detention water quality ponds also were designed to clean rainfall run-off in accordance with the Texas Commission on Environmental Quality requirements.
Community Involvement
The success of the MoPac Expressway Intersections project also can be attributed to the active involvement of the local community. During the planning and design phases, public meetings were held to gather input and address concerns from residents and stakeholders.
Cyclists were some of the most vocal residents who attended public meetings. They advocated for schematic design refinements to better accommodate their needs.
One cyclist organization requested a minimum 12-foot radius at the intersection for the 10-foot-wide shared-use path (SUP) lining the frontage road. The project team incorporated their suggestions into the final design, making a safe intersection for roadway and SUP users.
Robin Stallings, executive director of Bike Texas, as pleased by the collaboration.
“We appreciate the bicyclist and pedestrian improvements that TxDOT has made at MoPac at both Slaughter Lane and La Crosse Avenue,” Stallings said. “It is especially important to the current and future people of Austin to have transportation choices that include active modes, like bikes and e-bikes. Thoughtful design and engineering make our streets safer and provide a foundation for healthier citizens.”
Accessibility Improvements
The MoPac Expressway Intersection project prioritized accessibility and adhered to the Americans with Disabilities Act (ADA) guidelines.
Heather Ashley-Nguyen, P.E., TxDOT’s director of Transportation Planning and Development for the Austin District, said the intersection at MoPac and Slaughter Lane has set the foundation for implementation of more innovative intersections within the 11 county district.
“The DDI at Slaughter and MoPac is an excellent example of improved safety and operations through innovation,” said Ashley-Nguyen. “We are implementing various types of innovative intersection designs across the Austin District to address unique traffic conditions at each location, aimed at reducing crash severity and improving travel times.”
The design includes:
- Accessible pedestrian signals.
- Tactile warning surfaces to alert visually impaired pedestrians of the street edge.
- Ramps for people using wheelchairs and accessible pedestrian push button.
- Wide cross walks for heavy pedestrian use due to the nearby James Bowie High School.
- 10-foot shared use paths for pedestrians and cyclists.
Other accommodations include pedestrian refuge islands that provide safe space for all ages and abilities to cross the entire intersection in one signal phase.
State of the Art
The project incorporated interconnected traffic signal equipment with signal pre-emption for fire, EMS and police to enhance safety and efficiency.
These advanced systems were designed to optimize traffic flow, reduce congestion and the likelihood of crashes and accommodate emergency vehicles by allowing signal optimization during emergencies.
The new signals also respond to changing traffic conditions, allowing smoother transitions and less stop-and-go driving.
The MoPac Expressway Intersections at Slaughter Lane and La Crosse Avenue is a shining example of how thoughtful design and community involvement can improve road safety and provide environmentally friendly solutions. The project has set a high standard for future infrastructure developments in Austin and beyond.
The MoPac Expressway Intersections project serves as a model of what can be achieved through careful planning, innovative engineering and active community engagement. By prioritizing safety and sustainability, this project has improved the daily lives of Austin residents and provided a blueprint for others to follow.
For officials who conceptualized and executed the project, completing the Slaughter Lane intersection achieved more than just a reduction in crashes. It also represented a commitment to building a safer, accessible and more inclusive city.
The city’s population will increase by 750,000 by 2040, according to a recent study by Imagine Austin. This will lead to the need for continued alternative traffic solutions. RB
Robert D. Austin, P.E., is a project director at LAN.
