Designing safer crossings
Building on those findings, TxDOT partnered with Texas A & M University to find practical, science-based solutions to reduce collisions. The collaboration became one of the first projects in the country to connect ecological research with transportation management.
The engineers at the Texas A & M-RELLIS campus developed and evaluated prototype diverters to ensure they met highway safety standards and could withstand strong winds. Coulson and Tracy evaluated the efficacy of the prototype diverters in potentially altering monarch flight height above traffic height. The team then installed roadside diverters for field evaluation at two test sites: One in West Texas along Interstate 10 near Ozona and another at the Lavaca Bay Causeway on the Texas coast.
At the West Texas site, early results showed the diverters reduced monarch deaths by about 50 % during fall migration. On the coastal causeway, results were less consistent due to wind variability, providing valuable insights into future refinements. Permanent mesh barriers that can remain in place throughout the year are being considered.
“ Even modest changes in how roadsides are managed can make a measurable difference,” Tracy said.“ That connection between science and application is what makes this work meaningful.”
Understanding habitat interactions
The research also examines how roadside vegetation influences butterfly movement. Milkweed, the only plant monarch caterpillars can eat, and native wildflowers that provide nectar are often found growing in highway ditches and medians. These plants create critical habitat but can also draw butterflies toward traffic.
By mapping milkweed and the related vegetation zones alongside migration data, Coulson’ s team also advised TxDOT on potential adjustments to mowing schedules
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