The event yesterday morning was unremarkable -- motivational speakers at Mellon Arena -- but it nevertheless created traffic jams, parking difficulties and frayed nerves in the Downtown area.

Now, add to that intense security, protesters, closed streets and parking garages, no subway service and little or no bus service in the Golden Triangle, and it's easy to see how next month's G-20 economic summit has the potential to create perhaps unprecedented problems of Downtown ingress and egress.

But there's a positive difference between what might happen Sept. 24 and 25 when the G-20 summit is held at the David L. Lawrence Convention Center and what occurred yesterday, said Kevin Evanto, spokesman for Allegheny County Executive Dan Onorato.

"No one was thinking about [yesterday's event] and planning for it. We can prepare for the summit," he said. "Everybody needs to think ahead about it. We're telling people you should have some business continuity plan, we're telling people to treat it like a blizzard."

And that's already happening even though specific details of security perimeters and street closures won't be made public until shortly before the event.

Some schools, such as Duquesne University and Community College of Allegheny County, have already decided to close, and others are considering following suit. On the cultural front, the Pittsburgh Symphony Orchestra will postpone its season-opening weekend concerts of Sept. 25, 26, and 27 at Heinz Hall, moving them to open dates on June 4, 5, and 6, 2010.

And businesses are planning a variety of reactions, said George Mathews, chairman of the Three Rivers Contingency Planning Association, a group dedicated to making sure its 200 to 300 members can operate when the unexpected occurs. Members' plans range from business as usual, to having employees work from home, to temporarily transferring employees to other facilities in the area if they have them, to renting commercial space outside Downtown, to shifting work to offices in other cities if they have them.

"Many organizations already have plans for fire or floods or whatever the disaster may be. We're building around a worst-case scenario, we're working from our existing plans, looking at the particulars around this event. We're optimistic we'll get through it OK."

Officials at Highmark, which has 4,500 workers Downtown, are working on plans to minimize its employee base during the summit, asking many to work from home, adopt flexible scheduling -- perhaps by working more hours earlier in the week -- and other methods.

The company, which is headquartered in the former Horne's building on Penn Avenue, has the usual questions about transportation and parking, but also worries that it will be adjacent to exclusion zones around the convention center.

"It's going to be really, really problematic to get people in here," said Rob Yarsky, the company's business contingency planning director.

With the staffing cut, waits on the insurance carrier's customer service phone lines will probably be longer and health providers will be directed to the Internet for answers to insurance questions, Mr. Yarsky said. Its Blues on Call information service will not be curtailed, he said.

City Council President Doug Shields said Mayor Luke Ravenstahl and Mr. Onorato need to be more adamant in their statements to businesses, commuters and residents that "it's going to be a mess if you come Downtown."

"It's nice to put a good face on it, but I can't see how Downtown is going to remain anywhere near business as usual," he said.

Mr. Evanto said the officials are making information available as soon as it becomes available to them.

Joanna Doven, spokeswoman for Mr. Ravenstahl, said as much information is being disseminated as security concerns permit.

"Our goal as a government is to give people information they need at the time it is appropriate. We're not asking or even encouraging businesses to close. It is up to the businesses themselves on how to handle the traffic inconvenience.

"Our job is to prepare them for worst-case scenarios, directing them to resources for continuity planning," she said.

The Secret Service is in charge of security preparations for the G-20, which has been designated a National Special Security Event by the U.S. Department of Homeland Security.

Special Agent Darrin Blackford, a spokesman for the Secret Service in Washington, said it is working with local officials to set the security perimeters Downtown. He said the agency will make the information public as soon as possible.

"We understand the concerns of those Downtown residents and businesses," he said. "And we're going to do everything we can to work with them to make sure the city stays open for business."

Regardless of the inconveniences, the G-20's impact cannot be overstated, said Bill Flanagan, executive vice president of the Allegheny Conference on Community Development.

"We quantified the market value of the Super Bowl win at $1 billion. I can't even begin to calculate the market value, the global exposure, we're getting from this," he said.

"This opportunity doesn't come our way very often. It's in the whole community's interest to make the most of it, to put up with inconvenience for a couple of days. I think most people are willing to make that sacrifice for the good of Pittsburgh and southwestern Pennsylvania."