CHICAGO (CBS) — How do you plan for 45,000 runners and 1.7 million spectators at Sunday’s Bank of America Chicago Marathon? It starts months in advance, with the help of lots of people and technology.

In the middle of Grant Park is the marathon’s nerve center, called Forward Command. It’s a tent filled with phones, computers and lots of screens.

READ MORE: Jussie Smollett Trial: Lead Detective In Investigation Explains On Witness Stand How Smollett Went From Victim To Suspect

Race medical director George Chiampas said microchips and sensors allow them to track exactly where runners are.

“As the massive number of runners are heading towards a certain location, we can notify those teams in that area to expect that, but then additionally we can move resources; whether it be ambulances, supplies, as those runners move forward,” he said.

READ MORE: Chicago Weather: Slight Chance For Rain Wednesday Morning, Warmer During Day

That technology also allows organizers to track if a runner has left the course to enter a medical tent or drop out and take the bus back, and to notify that runner’s family.

Chicago Office of Emergency Management and Communications director Gary Schenkel said the 911 center has access to the city’s network of 27,000 cameras, as well as some from the private sector.

“We have many of the private businesses, etc., that will be readjusting their cameras appropriately along the racecourse, on the ingress and egress routes, and they’re going to retain any video should there be an incident, but they’ve given us full cooperation,” he said.

The first wave of runners gets started at 7:30 a.m. Sunday at the north end of Grant Park.

MORE NEWS: View Live Radar