Feb 26, 2009 9:27 AM

The second annual INRIX National Traffic Scorecard reveals a 30% decline in traffic congestion in 2008 during the peak periods on major roads in urban America.

Overall, the report found that 99 of the top 100 most populated cities in the United States experienced decreases in traffic congestion levels in 2008 compared with 2007.

The scorecard, produced by INRIX, a provider of traffic information, contains data on overall congestion and bottlenecks for nearly 50,000 miles of America’s major roadways.

It is compiled using tens of billions of data points from INRIX’s network of nearly one million GPS-enabled trucks and cars traveling across more than 800,000 miles of roads.

The report cites turbulent fuel prices and a struggling economy as sources for a consistent decline in overall traffic volume.

Detroit MI, where the jobless rate climbed past 21% in 2008, saw the second-largest decrease in congestion nationwide. Riverside CA, which ranked third-highest in the nation in foreclosure activity in 2008, saw the highest drop in congestion of the nation’s larger regions.

The top 10 most congested cities in 2008, according to the scorecard:

1. Los Angeles CA

2. New York NY

3. Chicago IL

4. Dallas TX

5. Washington DC

6. Houston TX

7. San Francisco CA

8. Boston MA

9. Seattle WA

10. Minneapolis MN