Millions of people in the U.S. celebrated and suffered under heat warnings as they flocked to beaches and traveled in droves to toast their nation's birth with July 4 parades, cookouts and the always anticipated fiery splashes of color in the evening sky. In Washington, neon bursts of light illuminated the night above the National Mall. The Boston Pops performed a musical fireworks spectacular at that city's Hatch Memorial Shell. And at parades all across the country, revelers dressed up in red, white and blue and waved the Stars and Stripes in commemoration of Independence Day. Video above: Fireworks fans take part in 'Blanket Run' to claim best spot for showTravel records were projected to fall with people jamming airports and crowding highways to reach Thursday's Independence Day celebrations, which will stretch into a long weekend for many. On the East Coast, some would-be beachgoers in Connecticut were turned away as parking at state parks along the shore filled to capacity, including a 2-mile (3 kilometer) stretch at Hammonasset Beach State Park — the state's largest shoreline beach.Across the West, meanwhile, residents dealt with stifling heat as the National Weather Service warned of a "significant and extremely dangerous" heat wave across much of the region.A heat advisory in Philadelphia that came with temperatures tipping into the 90s didn't stop crowds from gathering at historic sites in the city where the Declaration of Independence was adopted on July 4, 1776.Outside the National Constitution Center, volunteer actors dressed in Revolutionary War-era costume made of heavy wool, despite the heat. Participants said it was worth it."It keeps you connected to your neighborhood and where you live," said Adrian Mercado, who was donning a 6th Pennsylvania Regiment uniform.Evening fireworks were scheduled over the Benjamin Franklin Parkway, after a concert by Ne-Yo and Kesha.Fireworks crackled in backyard displays and an anticipated 16,000 professional shows were planned to light up the horizon from sea to shining sea.Millions of people were expected to watch the Macy's 4th of July Fireworks show in New York City, where cross rings, strobing comets, waterfalls and other effects can reach up to 1,000 feet (305 meters) in the air. Excited viewers crowded along both the New York and New Jersey sides of the Hudson River as dusk turned to dark, and they hoped rain would stay away. "This is how we celebrate. It's the bombs bursting in air. It's the rockets' red glare. That's how people show their pride and patriotism," said Julie Heckman of the American Pyrotechnics Association.All signs pointed to big celebrations: The Transportation Security Administration reported that a record of nearly 3 million people traveled through airports in a single day last week, a figure expected to be broken this week. AAA projected that 60.6 million people will travel by car during the holiday period. Part of the boost was attributed to easing inflation, though many Americans remain concerned about the economy.On much of the West Coast, residents were advised to take precautions to avoid overheating on the holiday. Temperatures topped 110 degrees Fahrenheit (43 degrees Celsius) on Thursday in inland areas of Northern California, with heat spreading into the Pacific Northwest. Some spots in the desert Southwest were expecting temperatures topping 120 degrees Fahrenheit (49 degrees Celsius). Hot, muggy conditions also permeated the Deep South and Middle Atlantic.The Northern California city of Oroville's annual fireworks were canceled although most of the 17,000 people under evacuation orders or warnings by the Thompson Fire were able to go home Thursday afternoon as hundreds of firefighters toiled under extreme heat.In suburban Chicago, Highland Park resumed its annual Independence Day Parade on the second anniversary of a mass shooting that took seven lives and injured dozens at the 2022 event. Residents gathered at a middle school for a remembrance Thursday before the holiday march, which followed a different route than in the past."July Fourth is always going to be a day of mixed emotion," Mayor Nancy Rotering said. "We come forth today hoping we as a community can remember and honor the lives lost."The holiday celebrating the establishment a new country, free from British rule, is traditionally marked by barbecue, cold drinks and the Stars and Stripes on flagpoles and on clothing, in addition to parades. But Americans were also celebrating in other ways unique to their communities. Of course, there was the annual hot dog eating contest on New York's Coney Island — where a new champion chomper emerged. Patrick Bertoletti of Chicago gobbled down 58 hot dogs to win his first men's title.In Alaska, the city of Seward got a head start with a fireworks display at midnight, as thousands of people gathered on a rocky beach to watch during the brief window where the sky dims in the land of the midnight sun. The shells burst over Resurrection Bay as people watched in silence. "It was absolutely magical," said resident Iris Woolfolk.The July Fourth holiday generally unites Americans in their shared love of country, but the 2024 version comes against a backdrop of deep political polarization and a divisive presidential race.In Boston, where tens of thousands were expected to enjoy the Boston Pops Fireworks Spectacular, conductor Keith Lockhart said it's inspiring to see people of different political stripes gather on Charles River Esplanade. But he noted that "one would have to have one's head pretty deeply stuck in the sand to not notice the deep divisions in our country." Associated Press writers John O'Connor in Springfield, Illinois; Isabella O'Malley in Philadelphia; Susan Haigh in Hartford, Connecticut; and Morgan Lee in Santa Fe, New Mexico, contributed to this report.