If you’re planning a driving trip to Canada or Mexico, you’ll need to pack more identification in the New Year, thanks to a new U.S. law.

Starting Jan. 31, 2008, U.S. citizens — both adults and children — returning to the United States by land or sea from Canada, Mexico or the Caribbean must carry a document that shows their citizenship. Those who don’t have a passport must carry a birth certificate plus government-issued photo ID, such as a driver’s license or school ID for young students, to show at border inspection stations. The new rule affects all vehicle and train travelers, cruise and ferry passengers, and private boaters.

In recent years, the U.S. Customs and Border Protection agency has urged travelers to carry a birth certificate and photo ID when traveling to those areas. The ID wasn’t a strict legal requirement, even though many travelers complied, but it will be law from Jan. 31 as the U.S. ramps up its border screening through what’s called the Western Hemisphere Travel Initiative (which grew out of the Sept. 11, 2001, terrorist attacks).

U.S. travelers who don’t have proof of citizenship — either a birth certificate or passport — will face secondary screening and delays at border stations while their citizenship is checked, said Mike Milne, a spokesman for the U.S. Customs and Border Protection agency. Non-U.S. citizens who live in the U.S. should carry proof of legal residency and their citizenship documents. Canadians trying to enter the U.S. without proof of their citizenship could be turned away.

Earlier this year, U.S. air travelers returning to the United States from Canada, Mexico and the Caribbean were required to carry passports under the Western Hemisphere Travel Initiative. The passport requirement eventually will be extended to land and sea travelers returning from Canada, Mexico and the Caribbean, perhaps as early as summer 2008. (For details on the ID law taking effect on Jan. 31 and the eventual land/sea traveler passport requirement, go to the Department of Homeland Security Web site, www.dhs.gov, and search for Western Hemisphere Travel Initiative.

Anyone planning to travel abroad who needs a first or renewed passport should apply now to beat the rush. The Passport Services Office gets busy each spring and could be swamped if the land/sea traveler passport requirement goes into effect next summer. Go to www.travel.state.gov/ passport/ or phone (877) 487-2778.