Confirming the worst fears of Boston commuters awaiting the arrival of the Democratic National Convention (search), security planners called Thursday for closing several miles of a major interstate highway during the afternoon rush hour and in the evening when delegates gather in July.

"Those decisions are not make lightly and they are not made in a vacuum," Secret Service security planner Scott Sheafe said. The Secret Service (search) is in charge of security for the Democratic convention, July 26-29, and for the Republican National Convention (search), Aug. 30-Sept. 2 in New York City.

A preliminary version of the plan, which called for closing a portion of Interstate 93 (search), blocking several highway ramps, and the weeklong shutdown of the commuter rail North Station, met with widespread complaints from commuters. Many said they would take vacation that week or telecommute from home rather than face a traffic nightmare.

All vehicles in the downtown area will be subject to random searches.

Boston Mayor Thomas Menino asked companies to give employees options, such as working from home, and to encourage carpooling.

About 24,000 rail commuters use North Station daily. Up to 200,000 motorists use the new I-93 tunnel, the centerpiece of the massive highway project known as the "Big Dig." (search)

The four commuter rail lines from the north will stop outside the city and riders will be bused into Boston. Subways will not stop at North Station during the convention.

Inner harbor commuter boat service from a wharf in downtown Boston also will be suspended for the entire week.