The moon will block out the sun, and day will plunge into night. Birds will stop singing, crickets will start chirping, and many people will gasp, weep, or even howl when they see the sun’s corona shimmering in the darkened sky.
And some drivers, inevitably, will stop in the middle of the road to take a selfie.
The Aug. 21 total eclipse will cut directly across 14 states, from Oregon to South Carolina. About 200 million people live within a day’s drive of the “path of totality,” and millions are expected to flock there for the event. Every other state, including Alaska and Hawaii, will see a partial eclipse.
Transportation officials are worried not only about massive traffic jams but potential crashes that could result from drivers focusing on the skies, not the road.
Officials across the country say they’re doing all they can to put out the word to eclipse-watchers, using press releases, videos, public appearances and social media. But in the end, they caution, it’s up to locals and visitors to follow common sense rules to stay safe.
“Don’t stand on the interstate. Don’t pull your car over. Don’t take a selfie from a bridge,” said Doug Hecox, a Federal Highway Administration spokesman. “The risk of driver distraction from this once-in-a lifetime event has never been greater. We don’t want anyone to have an ‘eclipse in judgment.’ ”
Lloyd Brown, spokesman for the American Association of State Highway and Transportation Officials, agreed that “an eclipse is clearly a transportation issue. We’re concerned that people will be driving down the road and just stop their cars and look up. They need to be safe in a situation like this.”
Officials are urging motorists to plan ahead and find a safe spot to view the eclipse. They say pulling onto the shoulder of a highway is a bad idea because it could block emergency vehicles from getting through and put drivers who get out to watch the event at risk of being struck by a car. And motorists on local streets need to pay special attention to pedestrians and cyclists, who may themselves be focused on the eclipse.
State transportation officials recommend that people find an event or designated location to safely watch the eclipse. Many state parks, for example, are hosting events or reserving areas to accommodate campers and day visitors.
But drivers, whether they follow that advice or not, could find themselves stuck in place for many hours, well after the eclipse has ended.
“People are thinking they’re just going to pop in, see it, and then turn around and head back home. They’re not,” said Dave Thompson, a spokesman for the Oregon Department of Transportation. “They need to be prepared for long backups and have a full tank of gas and stuff in their car like water and food and medications they might need.”
State transportation agencies are working with police and emergency management officials to plan for the major traffic jams many areas are expecting.
“The best advice is to find a safe location, arrive there early, stay put, and leave late,” said Matt Hiebert, a Missouri Department of Transportation spokesman who is heading up an eclipse task force for the state transportation officials association.
A total solar eclipse occurs when the moon completely blocks the sun. In the 14 states, there will be darkness for a few minutes in most areas of the eclipse’s direct path. In other parts of the country, the sun will be partially eclipsed by the moon. All phases of the eclipse from beginning to end will last up to three hours, depending on the area.
For many, the coast-to-coast total eclipse will be a once-in-a-lifetime event. The next one won’t occur until 2045.
The last time a total eclipse was visible across North America was 1918. That year, there were only 6 million cars in the U.S. In 2015, the latest year data are available, there were nearly 264 million.
Twenty-one interstates are going to be in the total eclipse’s band, the so-called path of totality.
As a safety precaution, many of the 14 states in the direct path plan to suspend road construction projects, according to Hiebert. But motorists who pass through them still need to be alert because there may be merged lanes, cones, barrels and other equipment on-site.
Another concern is that people may want to take photos of the eclipse while they’re driving, which officials warn would be extremely dangerous.
For anyone viewing the eclipse, the only safe way to observe it directly is by using special-purpose solar filters, such as “eclipse glasses” or hand-held solar viewers. Officials worry some people may wear the glasses while driving — another no-no.
“These glasses are designed to look at an intensely bright light, and you can’t wear them and drive,” Hiebert said. “It’s almost like wearing a blindfold. You won’t be able to see out of them.”
State transportation agencies in the direct path of the eclipse have been gearing up for the big event for months.
In Idaho, officials are estimating as many as a million people could descend on the state. The state transportation department has been working to identify locations that could become bottlenecks and trying to figure out ways to control traffic.
In Missouri, where officials are preparing for as many as 1.2 million eclipse-watchers, the transportation agency is coordinating with the highway patrol, which will monitor the capacity of state rest areas and welcome centers, where hordes are expected to gather. Once those areas reach capacity, troopers will shut them down, barring additional drivers from entering.
And in Oregon, which is expecting up to a million visitors and is experiencing a severe drought, transportation officials are concerned that the eclipse is occurring in the middle of wildfire season. They have issued an alert to drivers about how easily a vehicle can spark a blaze.
“If you pull into a weedy area and the undercarriage is very hot, your exhaust pipe can ignite a fire,” said Thompson, the Oregon spokesman. “Oil leaks can start one too.”
This article originally appeared on Stateline. Read more from Stateline.