A discount for regular drivers over the four Delaware River bridges went into effect Tuesday, and already 2,577 E-ZPass transponders have been registered on 1,869 accounts, said John Hanson, the Delaware River Port Authority's CEO.

The discount returns $18 each month to motorists with New Jersey E-ZPass accounts who drive over the bridges 18 times in a month.

PATCO posted information on its web site on how to sign up, and reiterated Wednesday that customers who register by Dec. 28 will have their trips over the bridge throughout the month retroactively apply toward the discount.

"Once you sign up you're in the program for as long as we have the program," Hanson said.

The discount is expected to reduce bridge revenue by about $6 million annually, Hanson said. Up to 29,000 people are eligible to participate in the discount program.