The number of cars that pass through the H-1 Freeway Zipper Lane each morning has dropped by more than a thousand, or about 26 percent, since the state increased the minimum occupancy requirement from two to three people in July.

State Department of Transportation director Brennan Morioka said while there are fewer cars in the Zipper Lane there are more people using it and they are arriving at their destinations about 15 minutes earlier as overall traffic in the crowded 15-mile corridor from Waikele to Downtown is down.

"There are more people in fewer cars spending less time commuting," Morioka said.

The Zipper Lane required at least three people per vehicle when it first opened in 1998. In its first year of operation, the lane was used by an estimated 2,300 cars each morning.

That minimum-occupancy requirement was lowered to two in 2005 after residents and lawmakers complained that the lane was underused.

Last July, the state increased the number of occupants required in vehicles using the Zipper Lane and the Nimitz Highway contraflow lane back to three, amid complaints that overcrowding caused traffic in the lane to move slower than in the general purpose lanes.

At the time, DOT officials said they hoped the move would relieve congestion in the special lanes by reducing the number of cars from 3,800 to 3,500 per morning.

The effect has been more dramatic. According to Morioka, an estimated 2,600 to 2,700 cars now use the lanes each morning, a figure that fluctuates significantly during summer months when schools are not in session.

However, Morioka emphasized that more people overall are benefiting from the Zipper Lane.

Morioka said the average commute in the Zipper Lane from Manager's Drive in Waikele to Pacific Street in Iwilei dropped from 32 minutes in 2007 to 17 minutes this month. In the general purpose lanes, the same commute has been shortened from 37 to 22 minutes over the last two years, he said.

"A significant part of this is that if we give people the right incentive — saving time — they will carpool," Morioka said. "By carpooling, they save 15 minutes on their commute. With more cars out of the general purpose lanes, people who drive by themselves also benefit."

That's news to Richard Oshiro, chairman of the Waipahu Neighborhood Board.

Oshiro used to take the Zipper Lane every morning, with his daughter as the second occupant in the vehicle. The lane was crowded, he said, but at least it continued moving when stalls or accidents brought the general purpose lanes to a standstill.

When the three-occupant rule took effect this summer, Oshiro, who works at The Queen's Medical Center, had to move back to the regular lanes. Now he has to make sure he and his daughter are on the road by 6 a.m. for a Waipahu-to-Downtown commute that all-too-often takes 75 minutes or more to complete.

"Initially, a lot of cars ended up coming out of (the Zipper Lane)," Oshiro said. "For the people that remained, it was pretty fast, but now there are more cars in the other lanes."

Oshiro said he'd like to see more flexible use of the Zipper Lane.

"I think it's underutilized," he said. "Maybe in the summer they could go back to two people. It would also be good if they opened it when there's a stall or an accident, because when that happens (the freeway) is a parking lot. There's not a lot of space out there, so we should maximize whatever lanes there are."

Morioka said there are signs of increased interest in carpooling. He also said that rising gas prices over the summer, coupled with the benefits of ride sharing — quicker commutes and less stress for passengers — has resulted in a surge of interest in the state's Vanpool program.

According to Morioka, the number of Vanpool vehicles has increased from fewer than 170 to an estimated 250.

"We're running out of vehicles," he said. "It's a problem, but it's a nice problem to have."