The Science of Being Seen At Night

As days are getting shorter and mornings colder for many of us, you may find yourself suddenly lacing up after sunset for night runs. But there are some obvious risks involved with running at night. Namely, traffic.  

The grim facts are this: According to the most recent data from the National Highway Traffic Safety Administration (NHTSA), more than a quarter of pedestrian deaths occur between 6 and 9 p.m. That statistic jumps up to 50 percent when the window is expanded from 6 p.m. to midnight. In 2017, 5,977 pedestrians were killed in traffic crashes. 

By understanding the science behind how humans see and react to objects at night, we can outline best practices and gear for making yourself conspicuous to oncoming traffic.

How Humans See

Humans have two visual processing systems. One is focal vision, which helps us see detail and recognize objects and colors. The second is ambient vision, a more primal system that helps us move around in our environments and gives us spatial awareness. This ambient system doesn’t require much light, and so it doesn’t feel challenging to navigate a curve in a car while driving at night. 

“All the visual information that we use to detect pedestrians and runners and cyclists in daylight, most of that information is severely impoverished at night time,” says Rick Tyrrell, a psychology professor at Clemson University who has done research on visual perception and night vision. “It can be virtually impossible to see a person on the side of a road in certain conditions.” 

No number can tell us how quickly all people respond to seeing a runner, but several studies have found that it takes 1.25 to 2 seconds for a driver to perceive an unexpected object, recognize it, then act by either slowing down or swerving to avoid hitting it. If a car is going 50 miles per hour, it can travel almost 100 feet in that time frame.

The good news is that the human visual system is extremely perceptive to biological motion, or the way that other human beings move. In fact, some research has found that newborns can recognize biological patterns after being alive for just a few hours. 

“We’re born with circuitry in our brain that helps us recognize other members of our species based on the patterns of movement that we see in them,” says Tyrrell. “We have an exquisite perceptual sensitivity to seeing the motion of other people, and recognizing that that’s not an ambiguous thing, that’s a person and that’s a person doing the following activity and traveling in the following direction.” 

How to Be Conspicuous

Practically speaking, this means that you want to be more than simply visible when you’re running. You must be conspicuous, meaning identifiable as a running human by oncoming traffic. There is a difference between the way a driver responds to noticing an ambiguous object and the way he or she responds to seeing a human being moving a certain way and then reacts properly. 

When it comes to being conspicuous to oncoming traffic there are two factors you need to consider: 

1. Create contrast. Contrast is the brightness of the person relative to the background against which we’re seeing that person. According to Tyrrell, the more contrast there is the better our chances are of being seen from father away. 
2. Create a sense of motion to facilitate quicker recognition by onlookers. By drawing attention to your motions, you help drivers’ quickly identify your movements as human and react appropriately.  

With this in mind, here are some apparel tips to help you stay safe when heading out to go on a night run.

Tip one: Wear reflective material, not bright material.

Wearing light colored clothing is insufficient to make yourself seen at night, and fluorescent clothing doesn’t work at all because it needs UV light to be converted into the bright colors we see. To be safe at night, you must wear reflective clothing and retroreflective clothing to shine by artificial light. 

Reflective clothing, like a mirror, reflects light back in all directions. Retroreflective material reflects light directly back to the source that it came from. While retroreflective material doesn’t look like it will do much when you’re standing, for example, in the room light of a store picking out gear, it is very effective at creating contrast in traffic light. 

“It doesn’t look special to the person who is wearing it, but it looks really powerful to the driver who is approaching you,” says Tyrrell. 

In fact, a 2012 study by Tyrrell and other researchers found that drivers correctly identified bike riders wearing a reflective vest 67 percent of the time; the rate jumped to 94 percent when ankle and knee reflectors were added to the bikers’ attire to highlight biological motion.

Tip two: Prioritize lighting your limbs.

Tyrrell notes that while a reflective vest or jacket can be beneficial, it is the part of the body that moves the least when we’re jogging. Instead, he says that we should concentrate on putting reflective material on our moving body parts. 

“Particularly our ankles, our knees, and our wrists and elbows, that can be a really powerful visual stimulus that tells oncoming drivers exactly what’s happening,” he explains. 

Because most car headlights are aimed low, make sure to have reflective material on lower extremities to reflect that light more brightly than material higher up on the body.

Tip three: Have enough reflective material.

To create enough contrast, the material you wear needs to be large enough to draw attention, making you shine out from the background. Though there isn’t enough research on what the minimum amount necessary to be seen is, we do know that more is better. A running shoe with a retroreflective tab on the back of the shoe can be helpful, but Tyrrell advises that runners use more material than would typically be seen on the back of a heel. 

Err on the side of caution by using more material than you may deem necessary, and distribute it in a strategic way to capitalize on biological motion. For example, sport a pair of socks with retroreflective material, or put a reflective band around your ankles, knees, and wrists. 

Tip four: Use a headlamp in addition to reflective gear.

You need to be seen, but you also need to see when running at night. Note that there hasn’t been much conclusive research showing that headlamps make runners more conspicuous to oncoming traffic. But, with this in mind, it’s a good idea to wear one along with retroreflective gear to help you light your path and see objects less obvious than a car that could cross your path on a night run such as a rock, root, street curb, hole, dog or even a night biker.

Tip five: Opt for red or yellow retroreflective clothing.

Studies show that red and yellow colors improve the ability of a pedestrian to be recognized at night.

Tip six: Assume you are invisible.

While drivers have a hard time seeing and recognizing pedestrians at night, the other half of the problem is that pedestrians dramatically overestimate their own conspicuity. When running at night we fast adapt to the darkness, so an oncoming pair of headlights looks intensely bright and impossible to miss. 

“Because it is so easy for the runner to see the headlights, it’s tempting to conclude that it’s just as easy for the driver to see the runner,” explains Tyrrell. “And that’s where the logic breaks down.” 

He emphasizes that the basic principle we must carry with us is the assumption that we are invisible. 

“We need to do everything possible to make ourselves conspicuous, but meanwhile act in ways that would keep you safe even if you are invisible to a person driving,” he says. “In other words, at night we really need to take responsibility for getting out of the way of oncoming traffic because, typically, they can’t see us very well.”