Transportation planners say there will be delays when Interstate 25 traffic is stopped in both directions during the presidential debate next week, but those who drive the stretch near the University of Denver everyday are expecting an unmitigated mess.

“It’s going to be a complete disaster,” said Angela Reed, who drives I-25 daily. “Seriously, it’ll be a total mess no matter what they say.”

The major north-south artery through Denver will be closed from 5 to 10 p.m. between Santa Fe Drive and Hampden Avenue while President Barack Obama and Republican challenger Mitt Romney debate at the Magness Arena on Wednesday.

Reed, an account executive for Ideal Home Loans, said she was immediately reminded of the snarled traffic when I-25 was closed from Sixth Avenue to Interstate 70 while Obama accepted the nomination at Mile High stadium during the Democratic National Convention in 2008.

“I-25 is a mess when there isn’t an issue,” Reed said.

Commuters looking for ways around the closure may be further frustrated because the event will shut some typical alternative routes across the south end of the city.

University Boulevard will be closed in sections at various times on debate day. Also, beginning at approximately 6 p.m. on Tuesday, Buchtel Boulevard will be closed from Franklin Street to University, with local eastbound traffic allowed onto High Street, according to the Colorado Department of Transportation.

“None of these decisions happen lightly,” CDOT spokeswoman Stacey Stegman said. “It’s always manageable, but always depends on the amount of traffic.”

She said if traffic is normal on Wednesday, the delays will be severe.

RTD spokeswoman Daria Serna said the entire bus and rail system will be running on Wednesday, although some bus routes will be detoured.

“People do need to plan for delays, though,” Serna said, “because you never know what can happen with an event like this.”

Bus detours are still being worked out, she said.

Candice Apicella, a sales analyst and I-25 commuter, said she understands the closures are necessary for security reasons, but was annoyed about the short notice.

“I have meetings that day that can’t be changed now, so I have to drive,” she said. “Why are we just hearing about this now?”

Stegman said the when and where of the closure had to be worked out with U.S. Secret Service and other law enforcement entities.

“We’re hoping that by working with the city of Denver, the Colorado Department of Transportation, elected officials and neighborhood associations we will get enough warning out there and people will be able to just avoid traffic delays,” DU spokesman Chase Squires said.

Still he said, travelers should be ready for anything the day that 3,000 members of the media and 5,000 debate observers converge on campus.

“It’s vital to stress that, as with any event of this magnitude involving candidates for the presidency of the United States,” he said, “everything is subject to change.”

Ryan Parker: 303-954-2409, rparker@denverpost.com or twitter.com/ryanparkerdp