Long Islanders love to run — especially in the summer. Registration for the popular New York State Parks Summer Run Series, a string of eight Monday night road races, opened at 9 a.m. Friday — and the 2,500 slots for the full series were long gone by noon.

“We are completely sold out,” said George Gorman, deputy regional director of New York State Parks on Long Island. “While the races have always been popular, over the past few years, it’s exploded.”

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The bulk of the registrations, which cost $70, were submitted online, but the parks office saved 500 spots for people who hand-delivered applications to the regional office at Belmont Lake State Park in North Babylon. Gorman said about 150 people were in line by 9 a.m.

Those shut out of the full series are getting a consolation prize: “second tier” registration to run four of the eight races is open for up to 250 people applying in person — an additional 1,250 slots open for online registration at 9 a.m. Monday, April 4. The half-series costs $55.

The Summer Run Series is an annual tradition Gorman dates back to at least 1984. Its scenic races tour a different state park each week. This year’s series begins June 15 with a 5-mile course at Heckscher State Park in Islip and wraps Aug. 3 at Jones Beach.

“It’s not just a run, it’s a social event,” Gorman says. “People come down and bring their families — it’s a great, great evening.”