Inauguration planners said Wednesday that they have improved crowd-control procedures that inadvertently prevented thousands from seeing the 2009 event as officials prepare for as many as 800,000 people to pack the National Mall on Monday for President Obama's second swearing-in.

"We've got a number of crowd management strategies that we're implementing this year to improve on some of the systems that were in place last time to prevent some of the issues that folks experienced with getting into the ceremonies," said Matt House, a spokesman for the Joint Congressional Committee on Inaugural Ceremonies. "Across the board, there will be improvements."

Obama's historic first inauguration, which drew a record 1.8 million people, was marred by clogged security checkpoints and, most notoriously, a backup in the Third Street Tunnel that kept thousands of people from seeing the Capitol Hill ceremony.

Security officials say they've added safeguards -- including additional metal detectors and electrical generators -- to prevent screening meltdowns this year. The troublesome tunnel will be closed.

Planners are also hoping residents and visitors will use a pair of smartphone applications and mobile websites to help navigate downtown, much of which will be cordoned off for security reasons.

"We've seen a big leap forward in how we're using new media, both to enrich this event but also to make it a smoother event," said Brent Colburn, a spokesman for the Presidential Inaugural Committee.

Inaugural festivities officially begin Saturday with a National Day of Service, but officials plan to tighten security dramatically beginning Sunday, when they start enforcing broader traffic restrictions.

Extensive road closures will be in effect early Monday, including Pennsylvania Avenue between 18th Street and the Capitol and 25 blocks of Constitution Avenue.

Three Metro stops -- Archives, Mt. Vernon Square and Smithsonian -- will also be closed throughout the day.

With large crowds expected, House said attendees should try to arrive by 9:30 a.m. to make it through security screenings. Former presidents will begin taking their seats on the inauguration platform at 11 a.m., and the hourlong program will start at 11:30 a.m.

Forecasters have warned of possible snow showers on Inauguration Day, and Colburn said officials would decide Sunday whether to proceed with outdoor events.

"We're not going to put anyone in harm's way," Colburn said. "Our hope is to be able to move forward with as many of these events as possible, regardless of the weather."

Colburn said, though, that it would likely take more than frigid temperatures to thwart the day's festivities.

"Cold doesn't seem to slow us down," he said.