DETROIT — Some businesses and lawmakers are worried that new identification requirements going into effect today at the borders with Canada and Mexico could create confusion and delays, and discourage some people from making the trip.

Americans and Canadians will be required to show some document to prove citizenship beyond a driver’s license. In the past, some people entering the U.S. from Canada or Mexico simply had to declare their nationality.

Ron Smith, a spokesman for U.S. Customs and Border Protection in Detroit, which has the busiest northern border crossing, said the agency will provide a grace period for travelers without the extra ID and will hand out fliers explaining the changes.

“The first couple of days, weeks maybe, could add a few seconds to the inspection process. But once people become aware of these requirements, and we’re getting the word out to them … those minor delays should disappear,” Smith said.

Earlier this week, 19 senators said in a letter to the Department of Homeland Security that commerce will be stifled and lives disrupted if federal officials proceed with the new requirements.

People who regularly cross the border at Rouses Point, N.Y., appeared to know about the changes. While not everyone has the needed paperwork, they said they were ready to comply, particularly Canadians who cross to save nearly $1 a gallon for gas.

At the San Diego border crossing, the nation’s busiest, the new rules have fueled concerns about longer waiting times.

Oscar Franco of San Diego, who visits Tijuana several times a week to see family, worries that his 4- and 6-year-old children won’t be able to cross on their birth certificates alone. (The new rules don’t apply to people 18 years and younger.)

“I have two little ones and I don’t know if they need a photo ID, or any other kind of ID,” said, Franco, 45, after waiting 90 minutes in his car.

In Texas, El Paso City Councilman Steve Ortega thinks the rules will reduce American travel in far West Texas, at least at first. “Over the long term, you will see the numbers start to rise up again once people get used to the new requirements,” he said.