CTRMA/Travis County Elroy Road Improvements

Improving traffic flow and flood safety near the Circuit of the Americas

Project Purpose

KFA provided drainage, water quality, and wet utility design for this collaborative project between Travis County and the Central Texas Regional Mobility Authority (CTRMA) to improve Elroy Road. Extending 1.25 miles from McAngus Road to Kellam Road, this project widens a narrow, two-lane roadway to an urban cross-section with four travel lanes, a center turn lane, bike lanes, and sidewalks. The improvements will make bicycle and pedestrian travel safer and increase capacity along this route, which provides service to Del Valle schools and is a key access route for Circuit of the Americas events, such as F1.

The roadway crosses the FEMA Zone AE floodplain for both Dry Creek East and Dry Creek East Tributary 7A. Besides adding capacity, one of the main objectives of the project is to elevate the roadway above the 100-year floodplain elevation, so significant vertical profile adjustments were made.

Project Approach

As a subconsultant, KFA provided drainage services including the following:

  • Atlas 14 impact, risk, and approach summary
  • Hydrologic and hydraulic (H&H) impact analysis including 2D HEC-RAS modeling
  • Plans, Specifications, and Estimate (PS&E) for storm drain, offsite/diversion channel, bridge class culvert, permanent water quality ponds in accordance with City of Austin (COA) regulations, temporary and permanent erosion control plans (SWPPP), and wet utility adjustments
  • FEMA Letter of Map Revision (LOMR) permitting (anticipated to follow construction)

Our team helped find solutions to the following design challenges:

Water Quality: Given the expansive floodplain on the project, it was not possible to meet the water quality objectives without placing the water quality ponds within the floodplain. Due to the location of the ponds in the floodplain, groundwater infiltration into the ponds was a concern. In response, KFA designed a low flow bypass and coordinated with COA Watershed Protection Department staff to implement lessons learned from pond groundwater mitigation strategies.

Roadway Alignment: While the new roadway centerline approximately follows the original alignment, it was adjusted slightly farther south for several reasons.

The readjustment helped contain channel grading along the north side of the roadway within the right-of-way to preserve a 24-inch COA water line and the Waters of the US for the Unnamed Tributary to Dry Creek.

At the highest point, the new roadway will be approximately 10 feet above the existing roadway. Since Elroy Road is the main access road for Circuit of the Americas, there are narrow closure windows between large-scale events. Realigning the roadway to one side (the south) meant we could construct half of the new bridge prior to impacting existing traffic patterns. The realignment also allowed us to phase construction to respect allowable closure times.

Roadway Overtopping: Raising the profile of the road impacted the hydraulic connectivity of Tributary 7A and the Unnamed tributary. We worked with the roadway design team to optimize the profile and designed parallel channels to manage impacts to the waterways.

Our drainage engineers collaborated with the rest of the project team to develop cost-effective solutions to each of these challenges. Design was completed in 2019.

Project Results

KFA is currently providing construction services for this project, including inspections, document control support, and construction phase engineering support. Construction is scheduled to be completed in 2021.