About the size of a large Golden Retriever, Florida panthers come in various shades of tan, with pale bellies and tails almost as long as their bodies. Also known as pumas, these endangered cats live mostly solitary lives, seldom vocalize, and hunt at dawn and dusk. No wonder that humans rarely encounter them—except on roads.

After a century of paying bounties for dead panthers, the state of Florida listed the animals as endangered in 1958; the federal government did so in 1967. In the 1970s, with wildlife officials uncertain whether a viable population remained, several preserves were established, and a panther recovery team was formed. Today, the entire population currently numbers fewer than 180 cats, according to the Florida Wildlife Conservation Commission. And as the panther population grows, it faces more risk on the road. In fact, collisions with vehicles are the leading cause of death for these animals: As of June 25, 2014, at least 12 Florida panthers had been killed by vehicles. In 2013, the toll was 15 and in 2012, 18.

The species once ranged across seven states, but in recent years, the entire breeding population has lived south of Florida’s Caloosahatchee River. That area likely has reached capacity, which means some panthers need to find new homes. In the process, they almost certainly will have to cross roads.

Road kill is not a problem unique to panthers, of course. An estimated one to two million collisions with large animals, such as deer or moose, occur each year in the U.S. Add in small animals—all those raccoons, armadillos and skunks you see flattened on the highway—and the number goes much higher. According to the Federal Highway Administration, vehicle collisions are a serious threat for at least 20 endangered or threatened species in addition to the panthers.

In an effort to save panthers, the state of Florida has installed warning signs and reduced speed limits in high-panther-traffic areas, but these haven’t proven to be very effective. So biologists have pinned their hopes on a more expensive but also more effective solution: Specially designed underpasses that allow panthers to get from one side of a road to the other without encountering vehicles.

These kinds of wildlife crossings—both underpasses and overpasses—have proven to be the most effective way to stop the carnage, according to Jon Beckmann, a biologist with the Wildlife Conservation Society. A Utah State University study found that two crossings on interstates in the state reduced vehicle-wildlife collisions in the area by up to 90 percent. (Engineers with the Utah Department of Transportation figure the structures paid for themselves in less than three years by eliminating costly vehicle repairs.) And in Canada, overpasses reduced mule deer and elk road kill by more than 90 percent, and in Florida, four culverts on a mile of U.S. Highway 27 that bisects Lake Jackson save hundreds of turtles and other animals every year.

In order for the crossings to be effective, they “have to be put in the right place, designed appropriately and maintained,” says Beckmann. The crossings typically have fencing to direct animals and vegetation to make them feel safe when using one.

So far, 59 panther crossings have been installed on about 40 miles of Florida highways, according to Darrell Land, Florida panther team leader for Florida Fish and Wildlife Conservation Commission. Based on reported collisions, these have significantly reduced localized panther road kill. Land has identified many other places that need crossings, and keeps an eye out for road maintenance or upgrade projects that he can piggyback a crossing project onto.

Florida also is currently testing use of roadside animal detection systems (RADs), which use light beams tripped by an animal to activate flashing lights to warn motorists. The University of Central Florida’s biology department is in the second year of monitoring RADs along a few miles of US 41 in the Big Cypress National Preserve. This is the first use of the system with animals the size of panthers (typically RADs are set for deer, elk and moose), so researchers are anxious to see whether the trips work and, of course, whether drivers pay any attention.

At least one panther-vehicle collision has occurred on US 41 despite the RADs. “There are a lot of hurdles for a system like this to be an effective tool,” says Land. “It’s a complicated system with a lot of moving parts, compared to a wildlife crossing with a fence that you can easily monitor and see whether it is in working order. I don’t think RADs will ever be a replacement for crossings.”

If you see a panther, report the sighting. That will help biologists identify areas used by these large cats and, just maybe, help keep them from becoming road kill.