State highway conditions are the best they've been in 19 years, according to an annual Reason Foundation study that measures each state's road conditions and expenditures.

The improvement is due to the recession; people are driving less, which has helped slow pavement deterioration and reduced traffic congestion and fatalities.

"We're seeing several factors combine to produce significant improvement in highway conditions," said David T. Hartgen, author of the report and emeritus professor of transportation studies at the University of North Carolina at Charlotte. "Over the last several years, states invested a lot more money to improve pavement and bridges. Spending increased 8 percent from 2007 to 2008, and per-mile spending on state roads has almost tripled since 1984, so you'd hope and expect to see improved performance. As pavement gets better, roads are widened and bridges get repaired, you'd also expect safety to improve. And the significant reduction in vehicle miles traveled during the recession has also played a role in slowing system decay. But as the states deal with large budget deficits and the recession continues, we'll have to wait and see if this progress can be continued."

According to the study, pavement conditions on urban Interstates are the best they've been since 1993, while rural primary roads are the smoothest they've been since 1993.

Across the country, 23.7 percent of America's bridges were structurally deficient or functionally obsolete in 2008, the lowest percentage since 1984.

With the recession reducing driving, and engineering improving road design and car safety features, traffic fatalities have steadily fallen to the lowest levels since the 1960s, the study found.

The Reason Foundation's 19th Annual Highway Report measures the condition and cost-effectiveness of state-owned roads in 11 categories, including deficient bridges, urban traffic congestion, fatality rates, pavement condition on urban and rural Interstates and on major rural roads, and the number of unsafe narrow rural lanes. National performance in all of those key areas improved in 2008, the most recent year with complete data available.

The Reason Foundation is a nonprofit organization that conducts non-partisan public policy research.

Overall, North Dakota, Montana and Kansas had the most cost-effective state highway systems in 2008. Rhode Island, Alaska, California, Hawaii and New York have the least cost-effective road systems.

Drivers in California, Minnesota, Maryland, Michigan and Connecticut are stuck in the worst traffic, with over 65 percent of all urban Interstates congested in each of those five states. But nationally, the percentage of urban Interstates that are congested fell below 50 percent for the first time since 2000, when congestion standards were revised.

Motorists in California and Hawaii have to look out for the most potholes on urban Interstates. In those two states, approximately 25 percent of urban Interstate pavement is in poor condition. Alaska and Rhode Island have the bumpiest rural roads.

Rhode Island has the most troubled bridges in the country, with over 53 percent of bridges deficient or functionally obsolete. In contrast, only 10 percent of top-ranked Nevada's bridges are rated deficient.

Massachusetts had the safest roads with just 0.67 fatalities per 100 million miles driven, while Montana and Louisiana had the highest, at 2.12 and 2.02 fatalities per 100 million miles driven, respectively.

Over the last two years New Jersey has moved up from last to 45th in the overall rankings, but still spends dramatically more than every other state. New Jersey spends $1.1 million per mile on state roads. The second biggest spender, Florida, spends $671,000 per mile and California spends $545,000 per mile. South Carolina had the lowest expenses, spending just $34,000 per mile.

To view the full report, click here.