In March 2014, Mickayla Friend and her boyfriend were walking along train tracks while traveling to their high school’s Sadie Hawkins dance in Marysville, California. The couple was unaware what of the train approaching behind them. The conductor sounded the horn and applied emergency brakes, but it was too late. At the last moment, Mickayla’s boyfriend pushed her off the tracks. He was killed. 16-year-old Friend was left in critical condition.

The story leaves one big question: how could a massive train creep up on the unsuspecting couple? The scary reality is that it’s more common than you might think.

“Statistically, every 94 minutes something or someone is getting hit by a train in the United States,” says David Rangel, deputy director of Modoc Railroad, a training school for future train engineers. Now, most of those incidents don’t involve people—Rangel’s statistic also includes the occasional abandoned shopping cart, wayward livestock, and other objects that somehow find their way onto the tracks. But, according to the Federal Railroad Administration (FRA), 784 people were killed in train-related accidents in 2013, the highest total in the last four years.

That accident rate comes down to a combination of factors, each increasing the likelihood of disasters. “Railcars are incredibly quiet,” Rangel says. “[Tracks] are designed to achieve the lowest possible coefficient of friction… At age 62, I could push a train car down a track.” Unlike a steam engine that would hammer the rails (a main reason why they were retired), modern railcars glide with low friction, and crushed rock underneath the tracks helps diminish impact. “You won’t hear it or feel it,” Rangel says.

The Doppler Effect, which explains how sound changes pitch based on an observer’s location relative to the sound’s origin (the reason sirens sound different as they approach you), plays a role. However, since they were in front of the train, where the pitch would be higher, they’d be more likely to hear the siren and doesn’t explain why they didn’t hear the train coming. Unsurprisingly, some train-collision victims often were wearing headphones or earbuds at the time. (These two were not wearing headphones.)

Terrain can also add to the danger. If a locomotive passes through a corridor lined with trees, those trees act like sound baffles in a recording studio, Rangel says, suppressing the noise. The average railcar traveling at 50 mph measures in decibels between at “loud voice” and a “shout,” according to the FRA. The horn itself, though, can be even louder than sirens on an ambulance.

Throughout his career, Rangel has two fatalities while operating a train. One of his two sons, who are also engineers, has four. The toll on the men and women operating these trains can be almost as difficult as the grieving families. “It never leaves,” Rangel says.

Several hundred tons of metal traveling at fast speeds would seem impossible to go unnoticed, but this false assumption claims lives every year. Your best bet? Just don’t go near train tracks.