Motorists in California, Minnesota, New Jersey and North Carolina have been stuck in some of the worst traffic in the United States, according to a study released Thursday.

North Dakota and South Carolina roads rated highest in the study's overall rankings, while New Jersey roads ranked the lowest. The study ranked Montana highways as the deadliest in the nation.

The study, based on data from 1984 through 2005, found that while road conditions have improved in recent years, traffic congestion and highway fatalities have increased slightly.

The state-by-state evaluation of highways was conducted by the University of North Carolina at Charlotte and financed by the Reason Foundation, a libertarian think tank based in Los Angeles.

With the federal highway fund running short of money for major highway projects, state governments are faced with having to pick up a greater share of the cost of building and maintaining highways.

Dr. David T. Hartgen, the highway study's lead author, says the results show that states need to prioritize, directing their transportation money to projects specifically designed to reduce congestion.

"Gridlock isn't going away," Hartgen said.

The study ranked highway systems in each state according to their cost-effectiveness, which was determined with several factors including traffic fatalities, congestion, pavement condition, bridge condition, highway maintenance and administrative costs. Evaluations were done on highways and all state-owned roads.

The five states with the most cost-effective roads, according to the study, are North Dakota, South Carolina, Kansas, New Mexico and Montana. The bottom five states are New Jersey, Alaska, New York, Rhode Island and Hawaii.

The study found that traffic fatalities rose by less than 1 percent between 2004 and 2005. Montana had the deadliest roads, with 2.3 fatalities per 100 million vehicle miles traveled. Massachusetts roads were the safest, with 0.8 deaths per 100 million vehicle miles.

Congestion rose by a similar amount. According the study, almost 52 percent of the nation's urban interstate highways were regularly congested in 2005, the last year included in the evaluation.

In a statement, Transportation Secretary Mary Peters said congestion has nearly tripled in metropolitan areas during the past 25 years despite increases in spending over that period. Resolving the issue has been a priority for the department, which last year announced a plan to combat gridlock through long-terms investments in key corridors.

"It's so important to get our transportation policies headed in the right direction — away from the federal government and back to the states and localities where innovation in America has always originated," she said.

Congress will have to find new sources of revenue if it wants to tackle the problems, said Matt Jeanneret, spokesman for American Road and Transportation Builders Association. His group estimates that Americans spend 47 hours a year stuck in traffic.

"This illustrates the capacity crisis that is facing this country, which is only going to get worse if trends stay the same," Jeanneret said. "We are bursting at the seams with motor vehicles and we're not adding capacity to that."

Janet Kavinoky, who works on transportation issues at the U.S. Chamber of Commerce, says the nation's traffic woes are at crisis levels. "There's more bad news coming," she said. "You hate holiday traffic? Pretty soon it's going to be business as usual."