I live where those turtle tunnels were built. The story behind them is instructive. Back in the late 60s/early70s when US 27 was built across an arm of Lake Jackson, cutting off that part of the lake. That stretch of road became the location of the highest rate of road kill turtles in the world - as many as 90 in one day. It was not just turtles. Documented are nearly 12,000 animals of 61 different species that were killed or observed crossing the road. http://www.lakejacksonturtles.org/#specieslist

Wildlife experts tried a temporary solution - fences to keep turtles from crossing the highway and that directed them to existing culverts under the highway - but with the fluctuations in the lake level and the numbers of turtles, those were not a permanent solution. Some turtles climb and simply climbed over the fence to get where they wanted to go.

The Lake Jackson Ecopassage which was built with help of stimulus funds and private donations provides a permanent barrier to animals trying to cross at locations other than the intended safe passage and a passage large enough for the observed species to pass between the main lake and the arm that was severed from it. It also makes that stretch of highway safer for motorist who no longer need to swerve to miss the animals that run across the road.

For more information about the Ecopassage: http://www.lakejacksonturtles.org/