Lucky for them, when it comes to the Christie Clinic Illinois Marathon, there's one man who's doing everything he can to keep them safe.
When Michael Minn runs, he thinks.
"I always think about the work that I'm doing. I'm a PHD student here at the University so I always got something on my mind about my research or my students," he says.
Minn also thinks about himself. He says he has to stay safe.
"You always have to look out for the people who aren't looking out for you," Minn adds.
But Scott Friedlein's job is to look out for runners, thousands of them. He's the emergency services coordinator for the Christie Clinic Illinois Marathon.
"You're talking about a course that goes 26 miles through Champaign and Urbana at a time when traffic is starting to build up and the race is not a short race by any means," he says.
The course winds through the streets, so keeping runners safe around traffic is a big concern.
"Every intersection that this race goes through is covered by somebody, whether it's a professional or a volunteer," says Friedlein.
Friedlein and his crew even go so far as to comb the streets looking for anything, like a pothole that could potentially injure a runner.
While Freidlein puts in a lot of hours planning for the worst, he also makes sure he's planning for things he can't plan for. He has barricade crews standing by on race day, in case they need to change the course for an emergency.
"Let's say we have a fire along the route, we have to be in a position to be able to alter that route sufficiently enough to be able to allow the fire department to be able to do their work and not stop the race," Freidlein says.
It's all an effort to make sure runners can think about whatever they want to when they run, and not worry about their safety.
It takes thousands of volunteers and a lot of officers to man the race.
Friedlein depends on help from the Champaign, Urbana, and Mahomet Police Departments.
He also uses resources from the Illinois State Police Department, and the Champaign County Sheriff's Department.
Between all of those agencies, about 75 officers are on hand race day.