Today, Mayor Nutter will unveil the result of a yearlong effort to map out citywide evacuation routes that will give anyone living or working in the city a better idea of what to do after a catastrophe.

The plan was prompted by the chaos in New Orleans after Hurricane Katrina in 2005. At the time, Philadelphia officials disclosed that the city did not have a comprehensive evacuation plan for moving masses of people out of harm's way.

The plan will be a critical tool for emergency responders and fill a big hole in the city's disaster preparedness, said MaryAnn Marrocolo, Philadelphia's deputy managing director for emergency management.

The evacuation plan outlines which roads will be used for what purposes: pedestrians, emergency vehicles, mass transit, private cars or a combination.

The city also is releasing a special evacuation plan for high-rise buildings. That plan identifies 14 places throughout Center City where evacuees would go for directions or emergency help. Each high-rise is assigned an emergency rallying point in an area like a park, a sports field or open space.

Today, too, the city will announce a service for people to get text messages or e-mail with emergency instructions. The alert system will also be available in Bucks, Montgomery, Delaware and Chester Counties. (To sign up, go to www.readynotifypa.org.)

"We're trying to manage chaos as best we can," Marrocolo said at a news briefing Wednesday.

The plan includes maps of each of the city's 25 evacuation zones, available online at www.phila.gov/ready.

In Center City, the plan calls for Broad Street to be open to pedestrians and all vehicles, but Market Street would be reserved for people on foot and mass transit.

The Schuylkill and Vine Street Expressways and I-95 would stay open for personal vehicles. The Benjamin Franklin Bridge would handle only foot traffic.

Marrocolo said different emergencies might call for very different responses. The release of a toxic chemical at the Sunoco refinery in South Philadelphia would warrant people sheltering in place, while a blackout in Center City could trigger an exodus.

"We don't know what's going to be in front of us," Marrocolo said.

She said her office planned to put evacuation maps in every police car.

The last time the city developed a citywide evacuation plan was in the 1950s, said Scott Knowles, a historian at Drexel University and an expert in the history of disaster planning. He said the civil defense office had held drills, shepherding people along the Benjamin Franklin Parkway.

After 9/11, the Police Department came up with evacuation plans for certain sections of the city, but kept them under wraps for security reasons.

The debacle in New Orleans, however, forced mayors across the country to ask whether they could handle a similar exodus.

In Philadelphia, the answer was a resounding no.

James Jordan, head of security for SEPTA, said Philadelphia was more likely to face a localized emergency - like a gas explosion, a high-rise fire or a flood - than a catastrophe like a hurricane triggering a citywide evacuation.

Even so, he said bringing everyone together to think through evacuation scenarios was a valuable exercise.

"This sets into motion a process that will allow us to respond," said Jordan, who participated in the planning.

In particular, he said, the high-rise plan, which identified 14 rallying centers, was "a significant advance in the safety of the city."

Philadelphia recruited Marrocolo, who used to be a planner for New York City's emergency management office, to head its emergency office a year ago. She made the creation of evacuation routes her number-one goal.

A team from 79 offices and agencies - including the chiefs of every police district - worked on the grid. The group also developed strategies for special situations, such as evacuating Center City high-rises, stadiums in South Philadelphia, and neighborhoods surrounding the Sunoco refinery or chemical plants in Frankford and Bridesburg.

The creation of a grid of evacuation routes is only the first step, Marrocolo said. She said emergency managers in Southeastern Pennsylvania were meeting monthly with their counterparts in New Jersey to work through scenarios that would force people in either direction across the Delaware River.

"It can't all be about pushing people out of Philadelphia," Marrocolo said. "It has to be able to be reversed." In other words, she said, how would Philadelphia handle an exodus from New Jersey into Center City?

Short of testing the evacuation plan under real circumstances, emergency responders in June will run through exercises built around evacuations of the South Philadelphia stadiums and Sunoco refinery, Marrocolo said.

"Evacuations are very messy, complicated operations that are basically managing chaos," she said. "All we can do is tell first responders how we want people to move."