# The Hidden Engineering of Wildlife Crossings

Channel: Practical Engineering
Source: https://www.youtube.com/watch?v=5mYpQWPtfpo
Recap page: https://rapidrecap.app/video/5mYpQWPtfpo
Generated: 2025-07-15T21:44:18.139+00:00

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## Quick Overview

Wildlife crossings, including the Wallace Annenberg Wildlife Crossing, are large-scale infrastructure projects designed to mitigate the severe ecological and economic impacts of roads on animal populations. These crossings, which can be overpasses or underpasses, are engineered to facilitate safe animal movement, reducing wildlife-vehicle collisions that cause billions in damages and hundreds of human fatalities annually, while also combating habitat fragmentation and genetic isolation in species like mountain lions.

**Key Points:**
- The Wallace Annenberg Wildlife Crossing, under construction over the 101 Freeway in Los Angeles, will be the world's largest wildlife crossing, costing $92 million.
- Roads cause over 1,000,000 wildlife-vehicle collisions annually in the U.S., leading to tens of thousands of human injuries, hundreds of fatalities, and over $8 billion in damages.
- Wildlife crossings are designed to accommodate different animal behaviors, including non-responders, pavers, avoiders, and speeders, with specific features like fencing and light considerations.
- Overpasses, like ecoducts and land bridges, are often the most effective for larger animals, blending into the landscape with native vegetation and providing clear sightlines.
- Underpasses, such as culverts and existing bridge structures, can also be utilized, sometimes requiring manual animal transport for species like amphibians.
- Habitat fragmentation caused by roads severely impacts migratory species and can lead to genetic isolation, as observed in Southern California cougar populations.
- Increased federal funding and advanced engineering guidance are driving the construction of more wildlife crossings, aiming to improve safety and ecological health.

![Screenshot at 0:00: Aerial view of the Wallace Annenberg Wildlife Crossing under construction over a busy 101 Freeway in Los Angeles, surrounded by green hills.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-00-00.png)

**Context:** Roads, while essential for human transportation, significantly impact wildlife populations and ecosystems. These impacts range from direct mortality through vehicle collisions to habitat fragmentation, which isolates animal populations and reduces genetic diversity. Recognizing these severe consequences, engineers and ecologists are collaborating to design and implement specialized infrastructure solutions known as wildlife crossings.

## Detailed Analysis

Roads fundamentally alter environments, posing significant threats to wildlife through habitat loss, fragmentation, noise pollution, runoff, and direct collisions. Over one million wildlife-vehicle collisions occur annually on U.S. roadways, resulting in tens of thousands of human injuries, hundreds of fatalities, and over $8 billion in damages. To address these issues, wildlife crossings are being built, such as the $92 million Wallace Annenberg Wildlife Crossing over the 101 Freeway in Los Angeles, which will be the largest of its kind globally. These crossings are designed based on extensive research into animal behavior, categorizing species as non-responders (like frogs), pavers (turtles), avoiders (bears, cougars), and speeders (deer). Design considerations include location selection using mapping and roadkill data, whether to build over or under the road (underpasses are often easier but require light and public exclusion), and specialized features like fencing with jump-outs or one-way valves to guide animals. Overpasses, like the ecoducts in the Netherlands or the Robert L.B. Tobin Land Bridge in San Antonio, are often more effective for larger, wary animals, blending into the landscape with native vegetation and offering clear sightlines. The increasing federal funding and engineering guidance for these projects highlight a growing commitment to ensuring infrastructure allows animals to move safely, benefiting both wildlife populations and human safety and economy.

### Impact of Roads on Wildlife

- Roads fundamentally change environments, leading to habitat loss, fragmentation, noise pollution, and runoff
- Over 1,000,000 wildlife-vehicle collisions occur annually on U.S. roadways, causing tens of thousands of human injuries, hundreds of fatalities, and over $8 billion in damages per year
- Roads can create a buffet for scavengers like vultures and raccoons, and provide housing for species like bats and swallows under bridges, but primarily pose a catastrophic threat to most wildlife.

### Types of Wildlife Crossings

- The Wallace Annenberg Wildlife Crossing, a $92 million project over the 101 Freeway in Los Angeles, will be the largest wildlife crossing globally, measuring 210 feet long and 174 feet wide
- The Federal Highway Administration has allocated $350 million for wildlife crossing projects across the U.S.
- Wildlife crossings can be overpasses (land bridges, ecoducts) or underpasses (culverts, existing bridges/viaducts, tunnels).

### Animal Behavior and Crossing Design

- Animals are categorized by their crossing behavior: non-responders (frogs, crabs) cross without regard for safety
- Pausers (turtles) hunker down when spooked
- Avoiders (grizzly bears, cougars) are intelligent and avoid roads, even low-traffic ones, leading to habitat fragmentation and genetic isolation
- Speeders (deer) are fast and alert, bursting across roads when given the chance
- Designs often target a 'focal species' with the hope it benefits others.

### Engineering Challenges for Crossings

- Fencing is crucial to funnel animals to crossings, requiring considerations for digging animals (buried fences) and escape routes (ramps, jump-outs, hinged doors)
- Underpasses need sufficient natural light to encourage use and support vegetation
- Overpasses must be structurally sound to support soil and vegetation, withstand elements, and be regularly inspected like human bridges
- Overpasses often feature flared approaches and walls to shield animals from traffic noise and light, blending into the natural scenery.

### Economic and Ecological Justification

- The average cost of hitting a deer in 2021 was $9,100, while a moose collision exceeded $40,000, demonstrating significant economic impacts
- Roads can lead to starvation for migratory species if they block access to food sources, as seen with mule deer after I-84 opened in Idaho
- Wildlife crossings are justified by both economic benefits (reducing collisions) and ecological benefits (maintaining genetic diversity and population health).

![Screenshot at 0:00: Aerial view of the Wallace Annenberg Wildlife Crossing under construction over a busy 101 Freeway in Los Angeles, surrounded by green hills.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-00-00.png)
![Screenshot at 0:40: Aerial view of a green wildlife overpass bridge with two tunnels for a highway, surrounded by dense forest in Canada.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-00-40.png)
![Screenshot at 1:28: A split screen showing vultures feeding on roadkill, a raccoon, and ants, illustrating how roads provide food for scavengers.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-01-28.png)
![Screenshot at 2:50: A screenshot of the Federal Highway Administration's 'Wildlife Crossings Program' webpage, highlighting statistics on wildlife vehicle collisions, injuries, fatalities, and costs.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-02-50.png)
![Screenshot at 3:45: A deer with antlers walking across a two-lane road in a mountainous, forested area, with a sign for 'Avalanche Area' in the background.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-03-45.png)
![Screenshot at 5:15: A graph showing the percentage of successful and killed wildlife crossings versus daily traffic, with a third line for 'repelled' animals emerging at higher traffic volumes.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-05-15.png)
![Screenshot at 6:00: An aerial view of a herd of pronghorn antelope standing in a field of green and brown shrubs, illustrating migratory species needing to cross landscapes.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-06-00.png)
![Screenshot at 7:15: A cougar with a tracking collar looking directly at the camera at night, representing the P-22 cougar whose isolation spurred the Annenberg crossing project.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-07-15.png)
![Screenshot at 8:58: A photo of a wooden ramp or 'jump-out' designed to allow animals to escape from the highway side of a wildlife fence, acting as a one-way valve.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-08-58.png)
![Screenshot at 11:50: An aerial view of the Robert L.B. Tobin Land Bridge in San Antonio, Texas, showing a wide, vegetated overpass connecting two natural areas over a six-lane parkway.](https://ss.rapidrecap.app/screens/5mYpQWPtfpo/00-11-50.png)