The radio said fog, not this. Not a wall of white that swallowed the overpass whole and left Dana Okafor staring at brake lights that weren't there a second ago.

She hit the brakes. The world behind her did not.

Metal found metal in a sound she felt in her molars, a crunch and then another crunch layered on top like a drumroll that refused to resolve. Her airbag punched her in the face. Somewhere behind her, glass rained onto asphalt in a sound like wind chimes made wrong.

She sat there, ears ringing, and counted headlights in her mirror. Three. Then five. Then she stopped counting because counting made it worse.

A man in a reflective vest was banging on her window before she'd even unclipped her seatbelt. "Don't get out," he shouted through the glass. "Stay in the car. They're still coming."

"Still coming" turned out to mean for another six minutes. Dana would later learn this from the state trooper's report, the way you learn the length of a fall only after you've landed. Six minutes of vehicles emerging from the fog at highway speed, drivers seeing brake lights a half second before their own bumpers met someone else's trunk. A delivery van. A school bus, thankfully empty, its driver already three days from retirement and now facing a hearing he hadn't planned for. A car hauler carrying six brand new sedans, which became six more crumpled hoods layered onto the pile like a child stacking blocks with no plan to stop.

By the time the fog burned off, there were forty-one vehicles fused into a single ruined organism spanning both directions of the overpass. News helicopters circled overhead. A meteorologist on the six o'clock broadcast used the phrase "advection fog" as though the words themselves might explain why a temperature differential over a river had been enough to erase forty-one vehicles' worth of stopping distance.

Dana walked away with a bruised sternum and a business card from a trauma counselor she never called. She told herself she was fine. She told this to her sister, to her coworkers, to the insurance adjuster who wanted to know the exact moment of impact as if a stopwatch could have been running.

What she didn't tell anyone was the dream. In it, she wasn't in her car at all. She was standing on the overpass, watching the fog roll toward her, and instead of being afraid she found herself doing math. If the fog moves at this speed and the cars behind me are traveling at that speed, how many seconds until the next crunch. She woke up each time still counting, the way some people wake up still falling.

Six weeks later, driving home from her sister's place, she hit a patch of fog on a bridge outside of town. Nothing, really. A hundred yards of gray, gone in under a minute. But her hands found the wheel like they were bracing for something, and in her mirror she caught herself glancing back, once, twice, counting headlights that weren't there.

The investigation eventually named a cause: a cold front meeting warm river water at exactly the wrong hour, a fog bank that formed in under four minutes and reduced visibility to arm's length. Forty-one drivers. One weather system. No single person at fault, the report concluded, which was meant to comfort everyone and comforted no one.

Dana kept the business card in her glovebox for a year before she finally called it. Not because of the bruise, which healed in three weeks. Because of the counting. Because some nights she still couldn't stop, and the number that scared her most wasn't forty-one.

It was that she kept waiting for forty-two.