WASHINGTON - North Dakota's roads rate higher than any other state in highway performance ratings released Thursday. The state also has some of the least gridlock.

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

North Dakota and South Carolina roads rated highest in the overall rankings; New Jersey's were the lowest.

"We are very proud of it," said Francis Ziegler, director of North Dakota's Department of Transportation. He says the state has maintained roads through maintenance that saves money in the long run.

The state-by-state evaluation 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 pay a greater share of the cost of building and maintaining highways.

David T. Hartgen, the study's lead author, said the results show that states need to set priorities and direct transportation money to projects designed to reduce congestion.

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

The study ranked highway systems according to their cost-effectiveness. That was determined using factors such as 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.

States spent almost $99 billion on roads they owned in 2005, almost 13 percent more than in 2004. New Jersey spent the most, almost $2.4 million per mile. South Carolina spent the least, at about $31,000 per mile.

Montana had the deadliest roads, with 2.3 fatalities per 100 million vehicle miles traveled. Massachusetts roads were the safest, with a death rate of 0.8.