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DENVER — A rare total solar eclipse will cross the U.S. on Aug. 21. It will be the first such solar eclipse to cross the U.S. from coast to coast in 99 years.

The path of totality, a 70-mile wide swath where the moon will completely block out the sun, will go through Wyoming and Nebraska, considered two of the better places to catch the event.

The Colorado Department of Transportation is encouraging drivers headed to the states to be prepared for traffic — lots of it.

Casper and Glendo in Wyoming are in the middle of the path of totality, meaning the total eclipse will last longer.

There are some estimates the population of Wyoming will double on Aug. 21 with the number of people making the solar pilgrimage and to be in the path of totality.

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Larimer County has set up emergency and weather alerts for the eclipse for drivers if they text “ECLIPSE” to 888777.

CDOT officials said to expect heavy traffic all weekend and on all highways headed to Wyoming and Nebraska.

CDOT is partnering with local first responders and the Colorado State Patrol as well as the Wyoming Department of Transportation to help manage the influx.

The agencies offered several tips to navigate the clogged roads.

Notably, they said drivers need to pay more attention, especially during the eclipse when others will be slowing down or stopping.

They asked drivers not to pull off onto the side of roads, use the center median crossings for turning around or parking, or park on a highway shoulder or in any ditch area.

Because the roads will be jammed, vehicles should have plenty of fuel. Drivers and passengers should also carry extra water and food as well as sunscreen.

Hotels and campsites have been sold out for months. And that day is also the first day for students at Colorado State University in Fort Collins and freshman orientation at the University of Colorado in Boulder that will add to the large amount of traffic.