There has been limited improvement in bridge conditions in the past decade but a substantial number of bridges in the United States remain in poor condition.

That’s according to a new report released by the Government Accountability Office in response to the May collapse of a bridge along Interstate 5 in Washington state, north of Seattle, where three people were injured when their cars fell into the Skagit River.

It found of the more than 607,000 bridges along the nation’s roadways last year, 1 in 4 were classified as deficient. Some are structurally deficient and have one or more components in poor condition, while others are functionally obsolete and may no longer be adequate for the amount of traffic they serve.

The good news is GAO found data indicating that the number of deficient bridges has decreased since 2002, even as the number of bridges has increased.

One difficulty it discovered is the impact of federal investment in bridges. While the U.S. Transportation Department tracks a portion of bridge spending on a state-by-state basis, the data does not include state and local spending, making it difficult to determine the federal contribution to overall expenditures. GAO says “understanding the impact of federal investment in bridges is important in determining how to invest future federal resources.”

The report also noted there has been progress in clarifying federal goals and linking federal surface transportation programs, including bridges, to performance. DOT worked with Congress, which adopted provisions in the current highway spending authorization, including ones that move toward a more performance based highway program.

GAO says Congress and the administration still need to agree on a long-term plan for funding surface transportation. It noted in a separate report that continuing to fund the Highway Trust Fund, which is used to pay for federal road and bridge projects, with a current shortfall in general revenues may not be sustainable without what it calls “balancing revenues and spending from the fund.”

GAO is not making any new recommendations. In 2008, it recommended that the Secretary of Transportation work with Congress to identify and define national goals for the federal bridge program, develop and implement performance measures, identify and evaluate best tools and practices, and review and evaluate funding mechanisms to align funding with performance.