It's a showdown that plays out every day: Two runners approach each other on the shoulder, one running with traffic and the other against. Who is running in the correct direction?

If there's a sidewalk, the law says that's where they should be. But if the shoulder is the only option, laws in the District, Maryland and Virginia say they must run against traffic. Maryland law, like the others, is clear: "If there is no sidewalk, always walk on the side of the road facing traffic." Although no federal laws mandate which side you should be on, the Centers for Disease Control and Prevention and the U.S. Transportation Department recommend running against traffic.

One study bears this out. Researchers in Finland looked at data from auto accidents from 2006 to 2010, covering about 2,000 miles and 258 pedestrian accidents. The researchers found that pedestrians walking against traffic have on average a 77 percent lower risk of being struck and injured by a car. "If no pavement or pedestrian lane is available," they write, "facing traffic substantially improves pedestrian safety."

The reason is simple — you can't react to something you can't see. Facing traffic, you can react quicker to a wayward — or distracted — driver. Jean Knaack, executive director of the Road Runners Club of America, encourages runners to go against traffic. "Running against traffic allows you to see incoming vehicles and to react to them," she says. "If your back is to incoming traffic, you're far less likely to react if a car is not giving you an adequate right of way."

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Dennis Barker is the head coach at Team USA Minnesota, where he has coached 24 national track champions and an Olympian. Seeing oncoming traffic is important, he says, so that the runner and the driver know what the other is doing. When he used to run on rural two-lane roads, he noticed that when cars approached and passed one another, they would move away from the center — and closer to the runner. Running against traffic allows you to notice this adjustment.

"As a driver, I appreciated others who walked or ran facing traffic because it helped me see them better when they adjusted their position as I approached," Barker says. "I, in turn, adjusted my position. We both took responsibility for each other's safety."

Runners should practice "defensive running" in the same vein as defensive driving. Defensive runners always look for oncoming distracted drivers encroaching their space. "Staying aware provides crucial time to avoid a distracted driver who may not be taking a straight line," Barker says. "A runner going with traffic is not aware of what's coming and is at the mercy of the driver."

Making eye contact with the oncoming driver allows you to see what's going on behind the wheel. Unfortunately, you may not like what you see.

The U.S. Transportation Department said that in 2015 there were nearly 3,500 fatalities and 400,000 pedestrian injuries because of distracted driving, primarily from people manipulating handheld devices. "Never assume a driver sees you. Try to make eye contact with drivers as they approach you to make sure you are seen," the agency recommends.

It's easier to be seen if you wear clothing that's a different color from your surroundings. Todd Straka, who publishes the Boulder Running website and is the race director for a popular Boulder 5k race series, says that runners should look more like bikers. "Bikers often have blinking lights, even during the day. I would suggest runners wear something like that so they can be seen from afar," he says.

Some people who run with traffic believe that if they are hit, the impact will not be as severe since they are moving in the same direction as the car. But physics proves this false. Rebecca Metzler, associate professor of physics at Colgate University, is a runner. Her rural community is two-lane roads, so she always runs against traffic. Metzler says that while the impact might not be as great if you get hit running with traffic, "you're probably going to get hurt either way. Your reaction time is far more important, and that smaller force is outweighed by the ability to get out of the way in the first place."

Wade Gordon, a retired Air Force colonel and an orthopedic trauma surgeon with extensive experience in traumatic and high energy injuries, agrees. "The force of being struck by a vehicle is great enough that it will break stuff, whether you're traveling with or against traffic," he says.

It's also not any safer to run in the direction of traffic on neighborhood roads, even though speeds might be slower. Todd Templeman, an emergency physician at Suburban Hospital, says that head injuries are especially common, and can even be fatal, at these low impacts. Templeman says that he runs only on sidewalks or running paths like the Capital Crescent Trail. "I never run on the road. Ever. There are too many safety issues. "

If you do choose the road, however, experts agree that you should never wear headphones because you can't hear the cars. One study examining pedestrian deaths from 2004 to 2011 noted the dangers of headphones. Headphones also cause inattentional blindness, which is the inability to notice unexpected objects even when they might be right in front of you. The cognitive function that you use to listen to music takes away from the more important cognitive function of seeing cars approach.

There are two instances, however, where running against traffic can be unsafe: as you approach the crest of a steep hill and as you round a sharp turn. The runner and the driver may not see each other until it's too late. If this happens, it's best to cross the road far in advance of the hill or the turn and run with traffic until it's safe to cross back over to the left side of the road.

Opipari is a former track coach and founder of Persuasive Matters, a legal writing consulting company. You can reach him at ben@persuasivematters.com .