Wildlife crossings are used to mitigate environmental impacts of a project by providing animals a way to safely cross roadways. These crossings also improve safety by reducing the chances of a collision between animals and drivers. Wildlife crossing structures should be considered when crash data indicates that the benefit of the crossing outweighs the construction and maintenance cost.

The type of wildlife crossing used must be decided based on site-specific criteria. In some cases, an overpass may be necessary to provide large animals safe passage over a roadway. In other cases, a small culvert could be utilized to carry water flow as well as give small animals a crossing underneath the roadway.

Two major factors in selecting the type of wildlife crossing are topographical constraints and minimizing impacts to the existing habitat. Understanding these variables will produce the most effective and environmentally conscious crossing

Refer to the and TxDOT’s – Chapter 9: Passes, Stock Passes and Cattle Guards for additional information and guidance.

Overpass bridges span over the roadway for both small and large animals, offering free movement across roadways as shown in . Bridge wildlife crossings should be sized based on the types of species needing passage. The designs must consider the surrounding land and features.

Underpass crossings allow animals to pass underneath the roadway without interacting with traffic as shown in . The vertical clearance will vary based on site-specific needs and species. Underpass crossings can also be designed as a dual-purpose water crossing.

Culvert wildlife crossings allow passage for wildlife to cross under roadways, railways, and embankments and can improve safety for the motoring public. These crossings utilize pipe or box culverts and are similar to underpass crossings, allowing movement beneath the roadway. These crossings can be designed in areas without water flow or at existing culvert crossings with water flow.

These types of wildlife crossing structures can be sized and located through coordination by the roadway designers with the District Environmental Coordinator and the ENV Division. Details can be obtained from the ENV Natural Resource Management Section and District Environmental Coordinators. When preparing structure plan sheets for cast-in-place or precast box culverts, designers should note that these culverts can have single or multiple openings allowing the passage of water, livestock, or wildlife under a roadway.

These crossings make use of culvert structures to provide wildlife passage underneath a roadway. Box culverts or pipes can be used depending on the specific needs of the project as shown in . Sizing of the crossing should be based on the wildlife intended to use the crossing. Refer to for additional information.

These crossings incorporate box culverts and pipes to allow both wildlife and water to cross underneath the roadway as shown in . The crossing should be sized based on hydraulic data and capacity requirements as well as on the size of the animals which will use the crossing. These crossings may also include dry walkways (1-ft to 2-ft high and 1.5-ft to 2-ft wide) within the culvert to allow wildlife easier passage through the structure. Refer to for additional information.

In some cases, culvert crossings may need to accommodate fish or other aquatic organisms. To facilitate passage for these types of organisms, lower hydraulic velocities and culvert slopes should be considered.

When barrier or rail is used, it may present a challenge for wildlife to traverse when crossing a highway facility. In these areas, the designer may consider using Hydraulically Efficient Barrier (HEB). While this type of barrier is generally used to increase hydraulic efficiency, it may also be used to allow smaller wildlife to cross the highway more easily due to the larger slot openings at the bottom of the barrier. Refer to for additional information and design details on HEBs.

Wildlife guards, with or without gates, may be used to:

Prevent livestock from entering the ROW and interfering with roadway traffic;
Maintain range control; and
Reduce animal-vehicle conflicts for wildlife.

To prevent livestock and wildlife from entering the ROW, construction of wildlife guards, often accompanied by fencing at side roads and private entrances, can be a cost-effective way to improve safety on a roadway. When placed near traffic interchanges on a crossroad, wildlife guards without gates should be placed at or near the access control line to prevent livestock and wildlife from entering a main roadway. The number of units will be determined by the width of the roadway, the number of private drives that need to access State ROW, and the types of wildlife or livestock that may enter the ROW. Some Districts have developed new types of wildlife guards with different types of bars and checked grates to reduce wildlife egress from private driveways. Designers can work with their District Environmental Coordinators and the ENV Division to determine the appropriate types of wildlife guards and fencing. See for an example of a grated wildlife guard and for an example of a round bar wildlife guard.

Fencing should be used to guide wildlife toward the crossing structure. The new structure will be unfamiliar to wildlife in the area and they may stray from using it and cross the roadway instead. The addition of fencing should help guide the wildlife along the crossing until they become comfortable using the crossing regularly. If the fencing is temporary the scheduled removal date should be specified in the plans.

Routine maintenance ensures the effectiveness of wildlife crossings. If left alone, the crossings could become overgrown or unusable. Coordination is required with Texas Parks and Wildlife Department for specific design requirements. Design crossings and culverts are required to meet TxDOT standards. For a further breakdown of different crossing designs, refer to the

Signing is a cost-effective safety countermeasure that can be used to alert motorists of potential presence of wildlife on or near the highway. The goal of these types of signs is to reduce the likelihood of vehicle collisions with wildlife and encourage drivers to be more alert.

See for additional information and guidance on the design of signing.