By the time slower runners reached the fluid stations, the water had already frozen.

Sunday’s bitter conditions were a harsh surprise for participants in the New York Road Runners’ four-mile Gridiron Classic, especially after a stretch of unusually mild weather, which had been attracting a growing number of people to weekly races in Central Park.

To improve the organization of their expanding events, the Road Runners were introducing wave starts that morning. The new system involves setting off groups of several hundred runners at a time, divided by speed. As 4,500 people lined up at the race’s start near East 68th Street, some expressed confusion and frustration over waiting in corrals.

“Maybe they shouldn’t have started it today because it’s so freezing,” a runner in wave six, Lucimar Araujo of Queens, said. “It took me a while to figure out where I had to go. And then we just stood there in the cold.”

A guidance counselor from West Orange, N.J., Angelo Stewart, bounced up and down, and shook his arms before the race: “I’m just going to try to keep moving. Either that or I’ll go wait in my car.”

The staggered starts are part of the Road Runners’ answer to concerns raised by the Central Park Conservancy and Department of Parks and Recreation over overcrowded races. With thousands of entrants each week, more and more runners are spilling out of recreation lanes and choosing to urinate publicly instead of wait in line for a bathroom, the president of the Central Park Conservancy, Douglas Blonsky, said.

Mr. Blonsky said he was considering capping the races if runners didn’t improve how they shared the park with the public. While saying he was pleased with runners’ behavior on Sunday, Mr. Blonsky said it was difficult to determine the effectiveness of wave starts. “Since it was so cold, there was not a lot of public in the park. We can’t compare it to a normal day.”

A spokesman for the Road Runners, Richard Finn, said easing congestion should curb inappropriate conduct. “Having one big group is what leads people to get anxious,” he said. “There’s this rush to the starting line and the Port-a-Potties, so people get impatient and go where they’re not supposed to. But that’s not an excuse.”

Although some runners are like Mr. Stewart of New Jersey, who said public urination “comes with the territory,” Mr. Blonsky said he’s surprised that offenders take their chances when witnesses are everywhere: “They’re pretty easily identified. Remember, they’re wearing numbers.”