If the traffic problems four days before Monday’s eclipse are any indication of what will be waiting for you when you travel to watch the eclipse, it’s going to be a really long day.   Be prepared.

“Imagine 20 Woodstock festivals occurring simultaneously across the nation,” said Michael Zeiler, an eclipse cartographer who estimates conservatively that between 1.85 million and 7.4 million people may commute into the path. But unlike a concert, there are no ticket sales for the eclipse, so no one has a definitive count of how many people will attend. The only thing experts can do is speculate.