A massive bridge in California that humans aren't allowed to use is set to finally open this year. Wallis Annenberg Wildlife Crossing is a massive infrastructure project nearing completion in Agoura Hills, Liberty Canyon, that provides a means for the area's rich array of wild animals to cross safely over a major throughfare.

The vegetated overpass spans the 10-lane Ventura Freeway, allowing local wildlife to cross between the mountains and the Simi Hills to the north. The reinforced concrete arch bridge expands their habitats and reduces the risk of them being struck by the 400,000 or so cars that pass under the bridge each day. Animal fatalities have been a major issue on the freeway, with more than 30 mountain lions struck and killed on it since 2002, as per the Harvard-Westlake Chronicle. It's also said to be among the leading causes of death for cougars.

Additionally, the lack of interconnectivity between the mountains and the hills has led to lion populations becoming isolated and declining, lacking the genetic diversity needed for a healthy genepool.

Conservationists proposed the structure as a solution that helps address the animal safety issue without disrupting road traffic.

Various organisations raised or donated money to the project, with the Annenberg Foundation putting up the most significant single investment.

The importance of that backing is reflected in the decision to name the bridge after the foundation's former president and chairwoman, the late Wallis Annenberg, who championed the endeavour.

The crossing, which is around 200 feet long and 165 feet wide, has a number of ingenious design features, including sound-dampening walls and light-deflecting materials to prevent animals from being startled.

Its wide dimensions also make it well-suited to creatures wary of the vehicles whizzing past close by. Meanwhile, the vegetation is composed of native plants to emulate the surrounding landscape, creating an inviting path for the area's abundant wildlife.

Besides Santa Monica lions, the bridge is also expected to a give a welcome new route for bobcats, bears, deer, foxes, and coyotes, who are also frequently at risk.

Work began in 2022, and the scheduled opening is now only months away. But getting to this stage hasn't been easy. The crossing had originally been set to open last year, but has faced delays due to environmental factors and flooding, The Guardian reports.

The disruption saw the budget rise from $93million (£68.6m) to the current estimate of $114million (around £84.1m), and the crossing quickly became the subject of ridicule from the right wing press.

Two writers affiliated the conservative think tank the Manhattan Institute wrote an op-ed published on Murdoch-owned news sites in which they described the project a "bridge to nowhere", dismissing it as a "jobs program for environmentalists".

It then became a target for Fox News, and even Donald Trump's Transportation Secretary Sean Duffy, The LA Times reports.

Beth Pratt, the National Wildlife Federation's regional executive director and public face of the project, acknowledged that the work has faced challenges but argued that cost reporting didn't account for inflation.

Speaking to The Guardian, the Boston native also insisted she wouldn't be deterred by detractors. On Earth Day last week, she announced that after years of hard graft, the crossing is now set to "open for animal business" on December 2.