The number of cars, trucks, SUVs and motorcycles registered in Hawai'i — 1.13 million as of last year — is creeping closer to equaling the state's total population of 1.28 million.

The registered vehicle count has climbed steadily each year since 1995, bringing with it a host of problems.

"All these cars add more pollution, leave us with less time with your family because you're stuck in traffic and costs us more to maintain more and more roads that are getting more and more heavily used," said Gail Grabowsky, an associate professor of environmental studies at Chaminade University.

The Big Island saw the largest percentage growth — 2.74 percent — when it added 4,390 cars, trucks and motorcycles. While Honolulu drivers saw less than a 1 percent increase in vehicle registrations, they still registered 5,002 vehicles in 2006, further clogging highways and testing Hawai'i's famous aloha spirit on the roads.

"All of this traffic density, as they call it, increases stress," said Leon James, a University of Hawai'i psychology professor. "When traffic density increases, there's a correlation between traffic and stress and traffic and driver relations."

There are no studies on how many cars and trucks Honolulu can ultimately handle, said Mel Kaku, director of the city's Department of Transportation Services.

No matter how many cars are on the roads, Grabowsky said, our ability to accommodate them is flexible.

"During the urban sprawl of the '50s and '60s, we didn't think about the repercussions of adding so many cars," Grabowsky said. "Are we close to capacity? To some people who live in Hawai'i Kai, we're well past the capacity. But the human species has an ability to be highly adaptable. We just get used to stuff."

Kaku said, "the sociologists are correct. We will adapt. But to what extent do we want to adapt? A commute that used to take 30 minutes 10 years ago has now creeped up to 45 minutes to an hour. There's going to be a limit of tolerance here that may be exceeded."

Kaku's own commute from his home in 'Aiea has jumped from 45 minutes five years ago to up to 90 minutes today.

"We've all seen slight increases," Kaku said. "Where you normally planned five, 10 minutes to get to an appointment, you now have to allow 20 minutes, 30 minutes just to be safe."

DAYLONG TRAFFIC NOW

And Honolulu's old morning, noon and pau hana rush-hour traffic patterns have given way to heavy traffic throughout each weekday and even on weekends, he said.

"There aren't these bell-shaped curves to our traffic patterns anymore," he said. "Now it seems we have just one continuous curve. It means more people are traveling over a greater length of time."

Kaku's department regularly watches vehicle registrations, housing development, construction and other issues to see if adjustments need to be made to traffic signals to adapt to more congestion.

A study under way of downtown traffic, for instance, could result in changes to the lengths of downtown traffic signals to make traffic flow more smoothly, he said.

A mass-transit plan for O'ahu, which calls for a fixed-guideway system to carry passengers from West O'ahu to the island's urban core, is designed to reduce traffic congestion by 10 percent overall by 2030. By then, however, planners expect congestion to be even worse than today because 30 percent more people are expected to live on the island.

Genevieve Giuliano, senior associate dean for research and technology and director of METRANS at the University of Southern California, said in an e-mail that Hawai'i has the potential to stem some of the problems experienced on the Mainland where "we are at saturation when everyone who can drive has access to a vehicle. ..."

ROAD-CONTROL TACTICS

"The island configuration limits both road capacity and where you can go in a car," Giuliano wrote. "The high level of tourism means that the state can impose some controls on the car rental market, and can think about transit alternatives for tourists. The quality of the natural environment may make strategies such as road pricing to control automobile use politically acceptable."

Professor Peter Gordon, of USC's school of policy, planning and development, also suggested in an e-mail that Hawai'i leaders consider controlling busy roads or highways through "time-of-day pricing" tolls that would vary in price according to peak traffic periods.

"Many people would think twice about the urgency of any trip if access were not free," Gordon wrote. "... Some trips would at least be postponed to the off-peak hours. Time-of-day pricing differences (like matinees, early-bird specials) would be the carrot and the stick. But make anything free and it can get crowded."

There are some signs that the expansion of Hawai'i's vehicle fleet may be slowing.

Between 2004 and 2005, Hawai'i's car registrations grew 4.43 percent. Between 2005 and 2006, the pace was slowed to only 0.88 percent.

And in the first quarter of 2007, sales of new cars dropped 11.7 percent compared with the first three months of 2006.

Even with new car sales slowing this year, the people buying new cars often trade in their used ones, which go right back onto the road.

BUYING FOR MILEAGE

"There has been some research that shows that with gas prices going up, people are buying more fuel-efficient vehicles," said Rick Ching, executive vice president for Servco Automotive, Hawai'i's largest car retailer and distributor of Toyota, Lexus and Scion. "But they're not necessarily getting rid of the vehicle they had. So they're holding on to their SUV and buying a more fuel-efficient vehicle and driving the one that gets the best gas mileage for each particular use."

Pal Eldredge just bought a new Toyota Tundra at Servco — his third new truck from Servco salesman Darrick Kaya since 2001.

Eldredge, who just retired as a Punahou School teacher, used to drive his cars to the end of their life spans.

Now, at age 62, Eldredge believes he's entitled to a new truck every couple of years. But he does wonder if he's doing the right thing for Honolulu traffic.

"This is something I've been thinking about," Eldredge said. "For every new car I buy and every new car somebody else buys, there's that many more cars on the road. Maybe I shouldn't be doing it because I think we're reaching the peak soon."

Around the country, U.S. drivers registered 246 million cars, trucks, buses and motorcycles in 2005.

The same year, Hawai'i drivers ranked near the bottom in per capita miles driven, averaging 7,907 miles per person per year, according to data from the Bureau of Transportation Statistics.

Only drivers in New York, Rhode Island, Alaska and the District of Columbia averaged fewer miles per person than Hawai'i drivers. But people in other states, such as Mississippi, averaged 14,442 miles per person in 2005.

Overall, the national average was 10,087 miles.

In an island state, "part of the difficulty is how few route options many of us have," said Kem Lowry, a UH professor of urban and regional planning. "If lanes are slow (or closed), we sit and stew."

Reach Dan Nakaso at dnakaso@honoluluadvertiser.com.