Construction operations in most cities around the country are not set to change on Aug. 21, when the US experiences a rare solar eclipse. But that's not the case in and around Portland, Ore., where the event will force a shift in how work crews deploy.

The sun will disappear behind the moon next month, turning an otherwise summer day of daylight into a twilight feel as part of what will be a total solar eclipse.

What is now dubbed the Great American Total Solar Eclipse will be most noticeable along a stretch of land between 60 and 70 miles wide, as it cuts across the country, from South Carolina to Oregon.

Scientists expect that the path will cut across Portland and the popular Oregon Coast in a 338-mile path from the Pacific Ocean to Idaho, generating an eclipse that will be at least 90% total everywhere in the state.

That powerful viewing opportunity has led the Oregon Dept. of Transportation to predict that the solar event may generate the largest traffic event in state history.

To prepare early, ODOT has announced that nearly all state-run construction and non-emergency maintenance on state highways in the path of totality will shut down Aug. 18-22 to ease the potential traffic impact, both for the eclipse day and for travel around the event. Other construction and non-emergency work will be curtailed depending on the expected traffic impact of the eclipse.

With hundreds of thousands of additional visitors expected in Oregon, fire danger will be especially high. A spokesperson for the department says that with no hotel and motel rooms available, rest areas and even roadside pullouts may have people camping in place, which presents a danger to safe highway operations and will exacerbate parking problems for commercial motor vehicles. Scale locations may be used for staging by law enforcement and emergency response vehicles and may not be available for use by commercial motor vehicles.

State emergency management officials estimate that more than 1 million people from out of state will come to Oregon to watch the eclipse on that day, flooding highways, single-lane roads and rural areas with vehicles, especially between the highly populated Willamette Valley and the Oregon coast.

ODOT expects the traffic to start before Aug. 21, but the bulk of extra vehicles will arrive early in the day, clogging the morning commute. Portland International Airport expects August to be the busiest in its history and rental car agencies are overwhelmed.

The popularity of the solar eclipse has Portland and surrounding areas expecting a massive influx that will force the state construction sector to press pause on an otherwise busy summer workday.

Follow Tim Newcomb on Twitter at @tdnewcomb.