By Matt Werner, Contributing Author
Hays County leaders knew improvements were needed to the intersection of Farm to Market (FM) Road 3237 and Ranch to Market (RM) Road 150 because of traffic and safety concerns in the area.
A group of historic trees complicated matters. Located near the intersection, the trees were treasured by the local community and Driftwood Historical Society.
Collaborating with residents and local leaders, engineers designed an innovative solution that preserved the local trees and made them a highlight for the high-speed approach roundabout.
“Hays County and our residents try to protect our natural landscape to the best of our ability,” said Hays County Commissioner Lon Shell. “Some improvements require tree removal, and we always do our best to reduce the number of trees removed."
Shell said that engineers were able to incorporate the significant trees into the design of the much-improved intersection to protect them. The trees also were an aesthetic feature of the project.
When designing a roundabout, one key safety aspect is sight distance for drivers. By having the historic trees in the center island, the new design had a natural safety feature.
“You want to strategically minimize sight distance for drivers entering the roundabout,” said road engineer Adam Pfeiffer. “Driver focus should be restricted to potential conflict points only affecting them such as vehicle traffic to the left and pedestrian crossings, so the trees became a really important safety feature.”
New Concept for Design
This was one of the first roundabouts built in Hays County on the Texas Department of Transportation system. While offering numerous benefits, roundabouts can often be met with resistance.
The previous T-shaped intersection had a sweeping right turn where drivers often didn’t yield as they should, resulting in many high-speed accidents. Roundabouts improve driver safety by reducing the type, severity, and frequency of accidents.
Well-designed roundabout layouts reduce the vehicle speeds upon entry and minimize relative speeds between conflicting vehicle movements, which results in a safer intersection design compared to a traditional intersection. Roundabouts have fewer points of conflict points as well, decreasing the opportunities for vehicles to crash into each other.
“Hays County considered multiple options for the improvement of the intersection,” Shell said. “The roundabout became the preferred option due to the improved safety and ability to efficiently handle the current volume of traffic now and into the future.”
According to crash data available from the Federal Highway Administration, roundabouts can reduce accidents involving injuries by 70% and result in a 40% reduction in the total number of accidents. Most importantly, roundabouts can reduce serious injury and deadly crashes by nearly 90%.
Collaborating with the residents and leaders, American Structurepoint engineers created videos and traffic animations that showed a roundabout intersection and T-shaped intersection with traffic signals that preserved the trees.
The videos were shown during public meetings and posted on the Hays County YouTube channel, with the roundabout video garnering more than 5,100 views. The roundabout design became the preferred choice.
Local Highlight Becomes Key Safety Feature
Often seen in more urban and low-speed settings, roundabouts on higher-speed facilities are becoming more common as leaders see the safety and traffic flow benefits of roundabouts.
“When you’re designing a roundabout with high-speed approaches, you want to include a lot of advance traffic calming features that intuitively slow drivers down,” Pfeiffer said. “Since this was one of the first roundabouts in the area, we included advance signing, curvilinear approach alignments, and raised splitter island medians to encourage incremental speed reduction so that vehicles operate at a safe speed at entry.”
The design team worked with Hays County and a local developer to ensure that one leg of the roundabout would adequately provide access to land where a mixed-use development is planned. The roundabout intersection, thanks to aesthetic landscaping and signage, also provides a gateway entrance to the Driftwood community.
Construction Constraints
Building the new roundabout posed several challenges because a complete intersection shutdown was not practical. Access to property owners was required to be maintained at all times, and the Hays City Store & Ice House, a popular destination restaurant at the intersection, operates seven days a week.
Engingeers created a multi-phased maintenance plan for traffic switches during construction. The roundabout was laid out and designed so that most of the construction could occur outside of existing traffic lanes.
This helped crews to construct a large portion of the roundabout without needing to alter traffic flow. The design also allowed some of the existing pavement to be reused. The new roadway was designed with a similar finished grade as the existing one, which made it easier for construction activities to switch to the next phase.
The narrow right-of-way area presented another challenge. The team balanced the horizontal geometry in the approaches to stay within the confined right-of-way. This design resulted in significant cost savings for Hays County by avoiding right-of-way acquisition and utility relocation costs.
The design also avoided a conflict with an existing buried underground telecom line and the ditch flow line. By using riprap on the channel at the utility to protect the telecom line in place, engineers saved Hays County an additional $8,000 in utility relocation costs.
Environmental Benefits
The roundabout isn’t just providing a safer way for motorists to travel. It also includes several environmental benefits that are important to the community.
The design included vegetative filter strips and grassy swales to improve the water quality within the constrained right-of-way area, meeting Texas Commission on Environmental Quality requirements.
Several communities in Hays County are designated as International Dark-Sky Communities. These communities show exceptional dedication to preserving the night sky through outdoor lighting ordinances and dark-sky education.
“There are a lot of local ordinances on lighting to reduce light pollution, so our lighting design incorporated those elements to meet their goals and protect the night sky,” Pfeiffer said. “Being Dark-Sky compliant was important to us to help preserve the local historic character.”
LED lighting and light shielding was incorporated to reduce glare and the amount of light reflecting off the roadway.
This solution complied with TxDOT design standards and local light ordinance requirements. In addition to preserving a key community asset, the lighting allows more visibility for stargazing, a popular tourist and naturalist activity in Hays County.
Preserving the trees and limiting light pollution were key aspects of the project, but at the heart of the project was improving safety. A year after opening, the county is already seeing the benefits of the roundabout.
“We have received many compliments from our citizens that often travel through the intersection as well as nearby businesses,” Shell said. “We have already noticed improved safety and are excited about the future of this area.” RB
Matt Werner is the public relations and communications writer for American Structurepoint, an architecture and engineering firm.
