HAMPTON, N.H. – Cars breezed through the southbound toll on Interstate 95 Friday, free. But officials said the real test of their experiment in traffic jam reduction will come Sunday evening, when thousands of weekend tourists pour out of New Hampshire and Maine.

Shortly after midnight, the state began a six-week experiment in which southbound drivers pay no tolls, while northbound drivers pay $2 for passenger cars, double the normal charge.

The idea is to reduce huge southbound traffic jams that usually occur on weekends.

At midafternoon Friday, northbound traffic backed up several miles south of the toll booth, just as it does on most other sunny summer Fridays.

But because of the experiment, officials were able to open 11 northbound toll lanes, one more than ever before, said Department of Transportation spokesman Bill Boynton.

Boynton said the extra lane appeared to make a difference, and by late afternoon there was little backup on the northbound side.

On the other side, southbound drivers moved through quickly – maybe a little too quickly, Boynton said.

“They are still supposed to obey the 35 mph speed limit,” he said. “Many were going considerably faster than that.”

Some officials in communities along the highway worried that some northbound drivers – especially commercial truckers who pay a larger toll than passenger cars – would take secondary roads to get around the toll.

Transportation officials were counting traffic on side roads Friday, Boynton said, but it was too soon to tell if drivers were seeking cheaper routes.

The secondary roads are already so traffic-clogged on summer weekends that most drivers would probably rather pay the toll, Boynton said. But he said that on quieter days, more drivers might try the side roads.