A week from now, motorists will be slogging through back-to-school traffic as more than 55,000 students return to class.

Motorists are being urged to leave earlier. Leave later. Carpool or vanpool. Take TheBus or TheBoat. Or even bike to work.

But most of all be aware that there will be more children in crosswalks and on bicycles. That was the state and city's message today about the annual "Beat the School Jam" program.

"The commute will be impaired next week in and out of town," said Brennon Morioka, director of the state Department of Transportation. "We will be suspending the majority of our construction projects for two weeks on O'ahu."

There are about 700,000 registered vehicles on O'ahu and about 905,000 residents, according to U.S. census figures.

"Traffic is the No. 1 impediment to our quality of life," said Mayor Mufi Hannemann. "We're here to focus on the short-term solutions from the city and state."

In anticipation of the crunch, the state raised the number of people required to ride in the H-1 Zipper Lane and the Nimitz contraflow lane from two to three people per vehicle. The lane had been moving slowly during part of rush hour before the change but now moves swiftly, Morioka said.

Since the changes went into effect on July 8, the DOT said, the Zipper Lane averages 1,730 vehicles each weekday carrying 5,190 people. General-purpose lanes handle 20,112 vehicles on average, with virtually each vehicle carrying just one person.

The HOV lanes on Kalaniana'ole Highway, and H-2 and Moanalua freeways will still require just two people per vehicle.

College students should take advantage of discounted U-Pass bus passes and leave their cars at home, said Wayne Yoshioka, city Department of Transportation Services. He also said TheBoat provides ferry service from Leeward O'ahu to Aloha Tower, with shuttles to UH-Manoa and Waikiki.

"This is a viable mode. Please take advantage of TheBoat," he said. "Mix and match your modes of transportation."

Vicki Harris, Vanpool Hawaii executive director, said that there are 300 vanpools in service now, making Hawai'i's the fifth largest program in the nation. Vanpool Hawaii pays for the van and its insurance while riders share the cost of gas.

"Let us help you beat the school jam," Harris said. "We want to encourage more to participate in a carpool."

BACK TO SCHOOL DATES

Start dates for big commuter schools and their enrollment:

Monday

• University of Hawai'i-Manoa, 18,818 students;

• UH-West O'ahu, 970;

• Honolulu Community College, 3,870;

• Kapi'olani CC, 7,451;

• Leeward CC, 5,738;

• Windward CC, 1,677;

• Chaminade University, 2,500;

Tuesday

• 'Iolani School, 1,840;

Aug. 28

• Punahou School, 3,769.

Source: State Department of Transportation