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The Science of Being Seen: A Guide to Safer Riding

What matters and why when sharing the road

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On a straight, flat, windswept section of U.S. 36 north of Boulder, I see a rider far ahead. At this distance, normally I wouldn’t be able to make out another cyclist, but the blinking red light, with an irregular low-low-bright-low pattern, is unmistakable, even from over a quarter mile away.

The rider, whoever he or she is, is one of many cyclists these days (including myself) who use rear and sometimes front lights, even in the daytime. But do these lights work as well as we think? And are lights alone enough?

In any discussion of cyclist visibility and safety there’s a victim-blaming undertone that it’s partly a cyclist’s fault he got hit if he’s not lit up like a runway at O’Hare—and this shouldn’t be the case. But the simple, physical fact remains that in any car-bike crash, the rider loses. So it’s worth asking: how can we make sure drivers see us? The answer might lie in the way we as humans process visual information.

RELATED: What It Feels Like to Be Hit By a Car While Cycling

Attention is Everything

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Driver reaction times can vary widely, but several studies find that for a driver to perceive an unexpected object, recognize it and act (either to slow the car or steer it away from the object) typically takes about 1.25 to 2 seconds.

In a stationary world, two seconds might seem pretty fast—but a car going 30 mph will travel at least 55 feet in those two seconds. Ramp the speed up to 50 mph, and the car will travel a third of the length of a football field before the driver can even move his foot to the brake pedal. And it’s imperative that action happens in those two seconds: a 2016 study in Sweden that measured how drivers pass cyclists on open roads found that most start to steer around the rider roughly 1.5 seconds before the vehicle reaches the rider. The math points to an unsettling conclusion: under normal conditions, if a car is coming at you and the driver doesn’t notice you, he won’t react in time to avoid a collision.

Worse, those reaction times are for an undistracted driver. Consider that it takes about four seconds to unlock an iPhone, which at just 30 mph equates to almost the entire length of that football field.

RELATED: How Far Would You Go To Create Your Own Bike Lane

Drivers Aren't Looking for Cyclists

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Every minute we spend behind the wheel, we’re also processing dozens, perhaps hundreds, of pieces of information: everything from the actions of the car ahead and the angle of the sun. Much of this information is processed subconsciously, and we direct our focus largely based where we expect to see threats.

One study that measured gaze behavior and reaction times among drivers at intersections found, no surprise, that drivers directed most of their attention to where they expected other cars to be. And while you might expect intersections to be the most dangerous, a surprising number of riders get hit on straight, continuing roads: about half, according to a 2012 study of 184 riders who were hit.

And while the majority of cyclists in the study attributed the crash to driver inattention, the authors, drawing on other research, underline the common refrain among drivers in these crashes: “I didn’t see him.”

That study, and several others, also points out that cyclists tend to overestimate our own visibility, in daytime but particularly at night. So part of why drivers don’t see cyclists could be that they're not looking for them, and part could be that cyclists think they're more eye-catching than they really are.

RELATED: 10 Things Cyclists Wish Drivers Knew

We Underestimate The Dark

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Overconfidence in our own visibility is particularly a problem at night, when we don’t see nearly as well as we think we do. We have two visual processing systems, explains Dr. Rick Tyrrell, director of the Visual Perception and Performance Lab at the University of Clemson. We’ve got focal vision, which helps us see detail and recognize objects and colors; and a deeper, more primitive system called ambient vision, which helps us move about in our environments and create spatial awareness.

“At night, it doesn’t feel like a challenge to navigate a curve in a car because the ambient visual system doesn’t require much light,” he says, but the focal system is degraded which we don’t often realize until some detail we didn’t notice, like a person on a bike, seems to suddenly materialize in front of us.. Adding to that false sense of security is the fact that the stuff we do see—road signs, lane striping and other cars—is all engineered to be highly visible at night. The result? Dr. Tyrrell says drivers consistently “over drive” their headlights, going faster at night than they should.

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Humans See Humans

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Fortunately, the human visual system “is exquisitely sensitive to biological motion,” says Tyrrell. He adds that our vision is particularly attuned to identifying humans as humans, based primarily on how they move. It’s a skill so engrained that it might be one of the first ones we develop: “research finds that newborns only a few hours old can recognize biological patterns” which help them differentiate people from other objects, he says.

One of Dr. Tyrrell’s research areas is human conspicuity to drivers, particularly at night. Conspicuity is slightly different than visibility in that it includes an element of identification; if visibility is seeing something, conspicuity is seeing what something is, which can change how we respond to it. “If a child walks next to the roadway and you fail to recognize it as a child... you can fail to recognize that the object might move in front of you,” Tyrell says. Correctly identifying an object, rather than just noticing it, can mean the difference between a driver simply reacting, and reacting properly.

The two key factors cyclists have some control over when it comes to conspicuity are creating contrast, which helps us stand out from our surroundings; and creating a sense of motion to spur quicker recognition. Research by Dr. Tyrrell and others shows that highlighting these areas of motion works best for drawing driver attention, and helps them more quickly identify the motion as human. For cyclists, that means the constantly rotating feet and knees, since our upper bodies stay stationary much of the time.

Wear Fluorescents In Daytime

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A 2004 meta-review of studies found drivers consistently recognized fluorescent colors faster, more consistently and from farther way than standard colors. Fluorescent material reflects non-visible ultraviolet light back in the visible spectrum, making it look about 200 percent brighter in daylight than conventional colors.

There’s no research on which color creates the best contrast, but flourescent orange is a good pick because it’s commonly used on highway safety and construction signs (ie. drivers associate it with caution), and orange is rare in the natural environment.

Keep in mind that fluorescents simply don’t work at night, when there’s no natural sun for the fabric to reflect. Artificial light sources like car headlights and street lamps don’t emit UV light either. At night your fluorescent yellow jacket is no brighter than anything else in your closet.

Wear Reflectives at Night

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At night, your best bet for visibility shifts from bright colors to reflective material, which shines (literally and figuratively) in artificial light. Since reflectives can be expensive and often impair the breathability of the garment, it’s important to be selective with placements—which brings us again to biomotion. A 2012 study by Dr. Tyrrell and other researchers found that drivers correctly identified a rider wearing a reflective vest 67 percent of the time; the rate jumped to 94 percent when ankle and knee reflectors were added.

RELATED: Brilliantly Reflective Cycling Gear

Dr. Wood and Tyrrell’s study didn’t address only ankle and knee reflectors (no vest) but he says that, if you have to choose, prioritize the lower-body reflective material. “A jacket has no movement, so a driver could see it as a road sign,” says Trek Product Designer Kurt Heggland. “When you put the reflective material in places that move, you become more recognizeable.” Also, reflective material higher up on the body may not capture and reflect as brightly from light sources such as car headlights, which are aimed low.

One thing to remember is to make sure you have enough reflective material. The reflective piping on lots of garments is simply too small to make a difference, says Dr. Tyrrell. To create contrast, the material must be large enough to draw attention and pop out of the background. For comparison, the minimum ANSI recommendation for reflective material on road workers’ apparel is 155 square inches, equivalent to a 10x15 square patch.

And don’t forget your wheels. “Reflective-sidewall tires are more effective than clothing in some cases,” says Trek’s Michael Browne. They’re so distinctly different from other reflective elements that, when drivers see them, they instantly recognize them as belonging to a bike.

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Use Lights Always

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Because they convey both brightness and a sense of motion, flashing lights work well even during the day. A 2012 study in Denmark found riders with so-called “permanent running lights” had a 19 percent lower “multi-party” crash rate than a control group without running lights.

RELATED: Ways to Glow In the Dark On a Bike

It sounds counterintuitive, but in the brighter ambient light of daytime, you actually need a more powerful light than at night. Rating brightness is sometimes problematic because light output is measured various ways and brightness also depends on reflector design, but 20 lumens is a good minimum output for a rear light in daytime use (more is better) . Flashing front and rear patterns draw attention and set you apart from your environment during the day, but at night, it’s best to use a steady pattern for the headlight unless you’re in a brightly lit urban environment.

Also, take care to angle the beam correctly; many rear lights have reflectors angled for maximum brightness when mounted on a seatpost. “In some of our research with rear lights, if the angle is off even 10 percent, brightness is greatly reduced,” says Jon Quenzer, an electronics design engineer at Trek.

See into the Future

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Improved batteries and technology like printable and flexible LED lights open up other possibilities for the future. For two years now, POC has shown a prototype wind vest and jacket with printed LED lights on the back, creating a flexible pattern of dots that creates a large total lit area out of very small light sources. Startup Lumenus is creating packs and apparel with built-in LED lighting on flexible strips.

But Dr. Tyrrell sounds a note of caution about going crazy with lights. “We don’t have enough data on how drivers process visual information,” he says. LED lighting, if not done well, could potentially confuse drivers who can’t quickly recognize what it is that they’re looking at. POC’s Huss says for that very reason, in developing the Light Vest, the company consciously decided to go with a gray/blue LED light color to mimic a reflective look.

The next step may not involve vision at all, but active safety systems similar to the emergency braking and lane-departure warnings that are already in place in many new cars. Garmin’s Varia radar system, for example, can warn riders of vehicles rapidly approaching from behind.

RELATED: The Best New Tech for Cyclists

And even more sophisticated technology may be coming. POC is in the second year of a collaboration with fellow Swedish company Volvo. At the 2015 Computer Electronics Show in Las Vegas, the companies demonstrated a technology that paired warning systems in the car to a rider’s helmet. “The car is connected to the cyclist with a cloud service, and the driver and the rider are both alerted to the other one, even coming around a corner where they couldn’t see each other,” says Huss.

The product is still a prototype demo, but Huss says it uses existing technology. “Everything is there,” says Huss. “It’s just about deciding what we want to do, and convincing the customer that they should pay for it.”

Perhaps, one day, autonomous vehicles will return fluorescent colors to the province of second-division Italian pro teams. Until then, when it comes to safety, grabbing as much attention as we can, as early as we can, remains our best bet.

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Headshot of Joe Lindsey
Joe Lindsey

Joe Lindsey is a longtime freelance journalist who writes about sports and outdoors, health and fitness, and science and tech, especially where the three elements in that Venn diagram overlap.

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