In Boston after dark, cyclists and runners look like fireflies, dots of light darting along sidewalks or zipping along bike lanes.
I’m one of them, lights shining front and back on my bike, fluorescent green jacket on my body, flashers blinking on my helmet. On foot, I feel conspicuous among a group of runners dashing up Winter Hill sidewalks, wearing a crossing-guard-style reflective belt and sometimes a headlamp, even though it never looks completely dark to me.
My running club hands out mesh vests with reflective stripes, in case you forget your own gear. “I want you lit up like Times Square,” our coach reminds us each fall when the days get shorter and no one wants to trade the road for a treadmill.
I used to feel confident that drivers could see me. But I recently learned I’ve been doing it wrong — and that I’m not alone. In fact, many New Englanders who exercise on dark winter mornings or evenings are unaware of what scientists say are the best ways to stay visible and safe.
Experts in the science of vision say most of us make two mistakes when it comes to running or riding in the dark. First, we put our lights and reflective stripes on the wrong parts of our bodies or bikes to grab a driver’s already splintered attention. Second, nighttime exercisers or commuters overestimate how easy it is for drivers to spot them, while drivers are similarly overconfident that they will spot people moving alongside them in the dark.
Let’s go back to the basics of vision: Our eyes have two kinds of receptors with two different functions. Cones see color in the day, while rods take over at night. Rods don’t see color, but they are very sensitive to motion, acting as lookouts in our peripheral vision.
Day or night, visibility is all about contrast — how much something stands out against the background. In the daytime, bright and sometimes fluorescent colors pop out so much because they bounce back the sun’s ultraviolet radiation. At night, that bonus sinks with the sun.
But there is one advantage at night that we can use if we rethink how to use reflectors — specifically, where to put them.
Exquisitely sensitive to human motion, our brains are highly adept at making sense of bright spots on a moving body. The brain interprets a dozen strategically placed strips of light on our arms and legs as a body in motion. Those signals — like constellations come to life — can be light from reflective tape on our moving ankles, amber reflectors on bicycle pedals, armbands on swinging wrists and elbows, or stripes on pumping knees.
Scientists call it “biological motion,” and studies have shown that even infants can perceive a human being on the move.
So can drivers.
“You want that driver to know exactly what direction you’re traveling in and predict where you will be when you arrive,” said Rick Tyrrell, professor of psychology at Clemson University. “Biological motion helps a driver predict the future.”
More commonly, however, the spots people choose to adorn with lights or reflectors are, when seen from behind, effectively fixed points: torsos, heads, bike fenders. Our body’s precious core might seem like the obvious place to highlight, but practically speaking, the reflective bands cyclists use to keep their pant legs out of the bicycle chain are more valuable because of the distinctive way legs move with each pedal stroke.
“Stripes on a vest can be seen, but they look like little bright spots. The visual clutter of little lights and reflections blends into the array and doesn’t look like a person,” said Fred Owens, professor of psychology at Franklin and Marshall College. “This is the sort of problem from a technical and scientific standpoint that we pretty much know how to fix, but it’s a matter of educating the road users and the policymakers.”
Another key part of that education is how our eyes adapt to the dark. Once we leave well-lighted indoor spaces, our eyes take about 20 minutes to adjust. After that, you may not be able to read a book, but you can easily make your way around.
Drivers never completely adapt to the dark, forced to face oncoming headlights, streetlights, traffic lights, and dashboard readouts. They think they can see what they need to, but studies have shown drivers overestimate how far and how well they see.
Similar research has shown that people who aren’t inside cars mistakenly think drivers on four wheels can see as well as they can on two wheels or two feet.
In self-defense, “push yourself into the driver’s awareness as much as you can” by exploiting biological motion, said Jonathan Dobres, a research scientist at MIT’s AgeLab. “Make yourself as big and bright and reflective as you can. You’re really helping the brain of a driver figure out, ‘Oh, that’s not a road sign, that’s a person moving around.’ ”
With so many users sharing the roads in the dark, drivers and exercisers can each be tempted to blame the other. Like the vision scientists, Brendan Kearney, communications manager for the nonprofit WalkBoston, takes no sides, but he offers practical advice to runners as they leave the relative safety of sidewalks.
“Just make sure as you approach the crosswalk that you see that [drivers] acknowledge you have the right of way,” he said. “You have much more to lose than the cars. They have airbags and you don’t.”
Survival guide for nighttime runners and cyclists
Scientists who study vision say a few interventions can help keep commuters and exercisers safe on winter nights.
1. Light up your joints: Add reflective stripes on your ankles, knees, wrists, elbows. Put together, they spell biological motion and tell drivers you are a moving person, not a stationary object.
2. Mix it up: Reflective gear works only when lights shine directly on it. Use reflectors on many sides: bicycle spokes, running shoes, gloves.
3. Don’t put all your faith in lights: Flashing lights are better than nothing but not sufficient by themselves.
4. Assume drivers just can’t see you: Make eye contact whenever you can, especially at intersections.
Share the road, share the rules
Drivers, cyclists, and runners have a better chance of navigating our crowded streets legally and safely if they all follow the same simple rules.
1. Slow down
2. Put down the phone
3. Look around
4. Obey the law
Elizabeth Cooney can be reached at email@example.com.