Two of the city's major transportation hubs will be closed during the Democratic National Convention (search) in July, an unpopular plan certain to snarl traffic but one that organizers say is necessary to ensure security.

The Secret Service (search), which is in charge of security, ordered the North Station rail hub to close July 23, three days before the start of the convention, and then reopen July 30, the day after the event. Interstate 93 will be closed during evening hours.

The convention is being held in the FleetCenter, which shares a building with North Station. Its four commuter lines from the north will be stopped outside the city, and riders will need to travel into Boston by shuttle bus. Subway service to North Station also will be suspended during the convention.

Street closures and parking restrictions around the FleetCenter have not been made final.

The decision to close North Station comes a few weeks after train bombings in Madrid, Spain, killed more than 100 people. The Secret Service recommended the security plan in coordination with city, state and federal officials.

The gathering of Democrats will be the first national nominating convention since the terrorist attacks of Sept. 11, 2001. Republicans meet Aug. 30-Sept. 2 at Madison Square Garden in New York City.