WSDOT uses tactics such as wildlife fencing, crossings, and median barriers to encourage animals to stay off highways.
Habitat connectivity is how well animals can move across landscape. Busy roads can create barriers to animal movements. They need to move from place to place for food, protective cover and in response to seasonal conditions.
Most animals can cross a road with low traffic volumes without a problem. However, these roads tend to be in rural areas where more animals live. This means animals cross more often which results in more vehicle collisions than on roads with high traffic. As traffic volume goes up, a vehicle is more likely to hit and kill an animal trying to cross. Eventually, animals mainly avoid a busy road and become isolated from animals on the other side of the road.
To encourage animals to stay off highways, we use specialized fencing, crossings, and median barriers. We monitor some culverts and bridges to determine the effectiveness and understand how animals use these structures. View this video to see a variety of animals using these structures.
We use fences to keep large animals off the highways. Studies show they reduce collisions between vehicles and large animals (mainly elk, deer, and moose) by 80 to 99 percent.
Gaps in fencing at intersecting side roads and on- and off-ramps are places where animals can gain access to the highway. To prevent deer and elk from entering the highway, we commonly use “wildlife guards” at these locations.
While fences keep animals off highways, they also serve as barriers to important resources for the survival and successful procreation. Combining fences with crossing structures either over or under the highway surface provide opportunities for animals to move past highways safely.
WSDOT designed a path under the new Casey Ponds bridge on U.S. 12 to provide safe passage for small animals under the busy highway. Grading and planting produced a more naturalistic setting. The safe passage opportunity at Casey Ponds will improve as plants grow and increase cover around the bridge.
WSDOT replaced the fish passage barrier on U.S. 97, north of Goldendale, with a structure large enough to accommodate both the stream and a variety of animals. This project has significantly reduced the number of deer-vehicle collisions in one of the state’s worst problem spots. Correcting fish passage barriers, like the one featured in these before and after photos, is also an opportunity to provide better conditions for all wildlife to pass safely under highways.
Median barriers are vital to preventing head on collisions. On highways with lower traffic volumes, wildlife benefit from highway designs that allow easy crossings. We use median barriers designed with a cutout in the base to allow small animals to get past them easily (see below). The cable barrier is another good option we use to allow the safe crossing of animals, as they can see past the barrier and are more likely to go around the cables.