It may come as a surprise that a professional road-marking company plays a crucial role in ensuring Chicago marathoners run their fastest times on Oct. 11. However, the dashed “blue line” painted on city streets by Naperville-based D2K Traffic is the shortest possible race route.

This line represents not only “a quick and efficient route to the finish line,” according to a statement released by marathon organizers, but also, “official measurements taken by city and race experts to ensure the Bank of America Chicago Marathon course is exact.”

For D2K Traffic, the process of painting the route is elaborate and time consuming. “It takes a crew from D2K Traffic about five hours of intensive work, completed overnight, to paint the line in its correct place,” marathon officials said. “After the race, the paint washes away with the rain.”

D2K Traffic worked last week preparing the blue line, now visible throughout the 29 neighborhoods of the 26.2-mile Chicago Marathon course, for the more than 40,000 runners who will toe the starting line on Oct. 11.

“For athletes leading the pack, and participants going after a personal record, knowing exactly where to run to complete the shortest possible route is crucial, avoiding any unnecessary added distance, no matter how small the inch,” marathon officials said in their statement. 

For the 2015 Chicago Marathon, it’s a road marking company that’s helping runners go the (least) distance.