Ask Sam: How Do They Decide Where to Put Deer Crossing Signs?

Feb 22, 2019

Every other Friday on Morning Edition NHPR’s Sam Evans-Brown tracks down answers to questions about the environment and outdoors for our listeners in a segment we call “Ask Sam.”

Nick from Flagstaff asks: “I’m wondering how do they decide where to put moose crossing signs. Is there any science behind it, and do they do any good?”

What an excellent opportunity to remind everyone of  the viral prank phone call from Fargo, North Dakota from a few years back: Donna “the Deer Lady.” If we don’t want people to hit deer, why not just put the deer crossings in low traffic areas?!

Now that we’ve all had our chuckle, how do they really decide where to put up a deer crossing sign? A rigorous, fact-based process, involving the mustering of data and expertise? No. They typically start with a request from a town where a crash has occurred.

“The crashes will typically prompt citizen request and that’s when we’ll start coordinating with Fish and Game to confirm whether there is a population or a natural crossing in a particular area,” says Bill Lambert, the state traffic engineer for New Hampshire Department of Transportation.

After they get a request to put up a sign, DOT calls Fish and Game to ask: are there *actually* deer or moose around here or was this just a flukey accident. That question typically lands on Kent Gustafson’s desk, the wildlife program supervisor over at Fish and Game. “Usually there are certain habitat parameters that kind of funnel the animals to certain locations,” says Gustafson, “Typically that may be where the most accidents occur so that would be the likely spot where they would put up a road sign or a warning sign for the public.”

So there are reasons why you might be more likely to hit a large cervid on certain stretches of road. If the road goes right down the middle of two big swatches of excellent deer habitat, that’s a risk factor. If there’s a gully, river, ridge or some other natural feature that wildlife want to walk along those will push them to cross the roads in certain spots. In fact, Fish and Game has gone through the trouble of trying to put together a big study of where you might find these New Hampshire “wildlife corridors.

So, there is some science behind animal crossings. Perhaps the best example of this is not deer or moose crossing signs, but ones that warn of turtle crossings. We have a couple of turtle species that aren’t doing so great—blanding’s turtles and spotted turtles—and Fish and Game has teamed up with a few towns that have known populations to warn drivers that lady turtles will be out roaming the streets come springtime, looking for a sandy spot to lay their eggs.

Mike Marchand, who heads up Fish and Game’s non-game programs, says these turtles are pretty rare, so you have to do more than just look at the landscape to know if they are present. “We know it because we’ve tracked turtles through that location and have telemetry information. Or we kinda have a combination; we know the animal’s there and we know there’s suitable habitat on both sides.”

Turtle telemetry! There’s some science for you.

But Do They Do Any Good?

Short answer: no.

“They’re not very effective at modifying driver behavior or animal mortality,” says Lambert.

The term that traffic engineers like Lambert use for deer jumping onto your car hood are “occasional hazards.” (Other examples: rock falls, mud slides, icy roads, or children at play.) And study after study have shown there’s not good evidence that you'll slow down after seeing a sign warning of a danger that will appear only very rarely. It might work the first time you drive that stretch of road, but eventually the warning just becomes wallpaper.

What makes this especially troubling to Lambert is that the signs keep propagating. He says they add two or three new deer crossing signs a year and “we very rarely take any down.” He says “there’s always going to be more new signs than there are signs taken away.”

But here’s a thought: what if you just put signs in the woods to alert the deer about the cars? Seems crazy, but I bet Donna the Deer Lady would agree with me.

Sam Evans-Brown, is host of NHPR’s Outside/In which you can subscribe to where-ever you get your podcasts. If you’d like to submit a question you can record it as a voice memo on your smartphone and send it to oustidein@nhpr.org, OR call the hotline, 1-844-GO-OTTER.

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