collision detection: The black-bear overpass

May 24, 2006

The black-bear overpass

Highway traffic is an enormous hazard for wildlife; thousands of endangered animals die every year after getting hit by cars and trucks. (To say nothing of the humans that die in these collisions -- slamming into an enormous black bear at 60 miles an hour is kinetically equivalent to driving into a brick wall.) Anyway, there's now an international movement afoot to build traffic overpasses and underpasses catered specifically to animals. A story in yesterday's New York Times Science section describes one that's located 50 miles outside Banff, Alberta:

Approached from the woods, the crossover resembles any other sloping hill, covered with brushy grass, shrubs, saplings and even a clump or two of pussy willow.
Earthen berms on either side hide the road and mute the noise of the tens of thousands of cars that pass by daily, winter and summer.

Animals have worn a trail along one edge and, at the top, leave prints on a cleared stretch of dirt, a so-called track pad, monitored by motion-sensitive cameras with night-vision lenses.

It's working: Researchers have counted tens of thousands of wolves, bears, cougars, and other animals using the overpass in the two years since it was built.

Now here's a really weird idea: Would this work in an urban setting? Though we tend not to think of cities as hosting much wildlife, in reality places like New York or Toronto teem with everything from squirrels to foxes. They run into problems with traffic too. A terrific story in a recent issue of New Scientist explaining why squirrels are so often greased by cars: They evolved over millenia to cross open spaces as quickly as possible without wasting time to check for predators, because there was nothing they could do hide in that situation, and any delay was just going to increase the likelihood that they'd get killed. (It's an open question as to whether squirrels will evolutionarily respond to the curious behavior of cars -- "predators" that move in predictable straight lines and can be avoided with a modicum of watchfulness.)

In the meantime, though, I wonder if a city could experiment with building little overpasses or underpasses for squirrels? They could actually be quite lovely -- metal or wood archworks spanning roads, festooned with climbing vines. Granted, squirrels are hardly endangered species, and it's possible that automobile deaths constitute an essential herd-culling that is keeping squirrels from booming in population, overrunning cities, and demanding voting rights. But at very least it'd be pretty hilarious to watch 'em scurrying back and forth across overhighway trellises!

Posted by Clive Thompson at May 24, 2006 11:22 AM

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Comments

"Granted, squirrels are hardly endangered species, and it's possible that automobile deaths constitute an essential herd-culling..."

I also wonder how many automobile deaths are caused by collision with the viscous squirrel population. ;)

Posted by: digital_blue at May 24, 2006 1:09 PM

They'll kill us all!

Posted by: Clive at May 24, 2006 1:31 PM

I think if you made squirrel passages, in order to make them popular, you'd have to make them needlessly complex. Almost art-like. Make them look difficult to cross. Squirrels are amazing at doing ridiculous jumps from our perilous surface to another. It would be like a constant squirrel circus. Just, no one tell PETA.

(Snicker, j/k of course)

Posted by: Peter at May 24, 2006 1:45 PM

One of the first such overpasses in the United States was built in 1985 just twenty five miles west of NYC, in my hometown of Berkeley Heights, NJ. For decades, environmentalists had blocked the completion of I-78 because it was going to go straight through the Watchung Wildlife Reservation. As part of the settlement to complete the highway, they built a few wildlife overpasses, which you could see from the highway because of the shrubs growing on them. Have no idea if they're effective, but is amusing to imagine deer hanging out and shouting obscene things at the passing cars, just like everybody else in NJ.

Posted by: Bunkysdad at May 24, 2006 2:23 PM

Here's a picture of one of them:

http://community.webshots.com/photo/463984948/2687364210066277896oyBDzF

Posted by: Bunkysdad at May 24, 2006 2:25 PM

There are people who argue that the solution to the squirrel problem (and many vastly more important ones) is to eliminate urban traffic altogether, by designing dense cities that are completely accessible by foot and bike.

http://www.amazon.com/gp/product/0865715521

http://www.context.org/ICLIB/IC08/Register.htm

http://www.ecocitybuilders.org/

Posted by: Bret at May 24, 2006 3:06 PM

Peter, heh.

Bunkysdad, thanks for the link -- very cool to see!

Bret, aha, yes, I'd wondered if there were a movement afoot to do that!

Posted by: Clive at May 24, 2006 3:28 PM

Clive,

Call your alderman! I'd be happy to make circus squirrel trellis bridges in NYC. Heh.

I've always kind of wondered why animals haven't adapted to cars… I know evolution is usually kind of slow, but given how quickly most small mammals reproduce, it would seem like they've had enough generations behind them to wise up to traffic.

Posted by: johntunger at May 24, 2006 3:37 PM

Glad to see more over and underpasses being built in the US. The salamander crossing was a decade ago now... I thought we'd see more of that kind of thing.

Regarding urban (grey) squirrels, they don't need complete trellises to cross roads. Two trees whose upper branches come within (roughly) 2 metres of each other is sufficient - squirrels are extremely well adapted to arboreal living. Here in Manchester UK, trees are very well distributed and the number of squirrels lost as roadkill is, I'm very proud to report, neglibible.

Posted by: Chris Bateman at May 25, 2006 2:52 AM

Just to provide another example, the town where I live, Davis, has the famous toad tunnel.

Posted by: Stephen Stralka at May 25, 2006 1:01 PM