As the 48th AJC Peachtree Road Race wrapped up Tuesday morning, some crossed the finish line on stretchers, and one runner even collapsed in cardiac arrest.
In some cases, heat and humidity were to blame, as temperatures increased to the 80s, according to Channel 2 Action News.
Several people reported dehydration and exhaustion at the race, Atlanta fire spokesman Cortez Stafford said.
The runner, who collapsed about 10 a.m., was given CPR and taken to Atlanta Medical Center, officials said.
He was alert when loaded onto an ambulance and is expected to be OK, Stafford said.
The incident caused temporary backup as runners had to shift into one lane to finish the race, according to Channel 2.
By noon, lanes had reopened.
The race had an unofficial 55,320 finishers, and there were no fatalities reported, according to results from organizers about 4 p.m.
Dr. Arthur Yantze, who worked the main medical tent at the race, said there were few serious incidents and no more heat-related incidents than last year.
Race participants and good friends Michelle Baskett and Tracy Fields said this year the heat has been much more tolerable than last year.
"I've made sure to drink water at each water station," Fields said.
PHOTOS: AJC Peachtree Road Race 2017
That was a key recommendation organizers warned participants to follow early.
A red alert was issued Monday for racers to take precautions for hot and humid weather conditions, according to Atlanta Track Club organizers. It remained in effect through the race.
“We want to get the word out that people should start hydrating and may need to adjust their race day plan in terms of pace and whether they should participate, should they have medical conditions made worse in this weather,” the Atlanta Track Club said in a statement Monday.
Even though the race lured thousands of participants, traffic remained light through the event, with few issues despite the Peachtree Road closing from Lenox Road to 10th Street.
There were, however, long waits reported at the Doraville MARTA station early Tuesday due to service delays.
“There was a small mechanical issue that created the initial delay,” MARTA spokesman Erik Burton said.
But the problem, affecting the northbound line, was wrapped up in about an hour.
WATCHING AND RUNNING
Heather Feldbauer, a first time runner from Ogden, Utah, said this is one of the largest races she has ever run in.
"This is a big crowd, so I don't even know what to expect," she said.
Feldbauer waited to hop on MARTA toward the Buckhead exit, where most runners were getting off.
Transportation to the race has been smooth, she said, adding that parking was easy.
But added security measures are creating some frustration.
There is a security checkpoint checkpoint outside the area where runners are herded. There, spectators have to empty their handbags and backpacks into clear plastic bags before entering the gates.
This is a precaution, Kirsten Widner, whose husband completed the race this morning, has never seen before.
"You're making it harder and harder to be a spectator," Widner told event staff as she dumped personal items into two different clear plastic bags.
Widner said she understands and appreciates the safety measures taken after the Boston Marathon was bombed in 2013. But she said wished the event had alerted spectators to the extra precautions. She said she would have brought a smaller bag.
"I almost missed my husband at the finish line,” Widner said. “Now I can't be with him as he gets his snacks. I'm just frustrated."
Still, participants didn’t let checkpoints deter them.
Richard Kalask, a six-time participant in the race, had a double hip replacement and still came out.
“I can't run competitively,” he said. “I just do it for fun."
Gail Bierenbaum came with her daughter to see her husband and another daughter participate in the race.
Gail said her husband has run every year for the past 20 years, except one when he had a double knee surgery.
"He healed and ran it the very next year," Gail said.
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—Curtis Compton, Chris Joyner and Ann Ondieki contributed to this story.