Last week’s I-35W bridge collapse in Minneapolis could be a warning—a modern day canary in the coal mine—that much of the country’s infrastructure is teetering on the edge of falling apart. Or this tragedy could be, as some civil engineers have argued, an isolated anomaly that affected one small part of our vast transportation system.

One thing we do know for sure is that lawmakers across the political spectrum have a hard time prioritizing the nation’s spending. In recent years, earmarking has become a primary means of avoiding tough choices. Members of Congress use political calculations to make backroom decisions about which pet projects get funded, rather than basing those decisions on project merit or cost-benefit analyses. This process is largely shielded from the public, leaving little opportunity for accountability or scrutiny.

Lack of prioritization is a huge problem for our nation’s transportation system. Take the 2005 transportation bill as an example. Transportation spending increased by $12.5 billion per year over six years, yet twenty-percent of that increase was used to fund a significant increase in earmarks. This bill contained 6,373 earmarks worth more than $24 billion. And to make matters worse, Congress did so amid ample warnings that the Highway Trust Fund (HTF) would be broke before the bill expired. Even after it become well known that the HTF could be hundreds of millions in the red by fiscal year 2009, another 1,400 earmarks worth more than $2.2 billion were added by the Congress and the administration to this year’s House transportation spending bill.

TCS and others have frequently warned against ignoring unglamorous public investments like infrastructure maintenance and improvements. The American Society for Civil Engineers and U.S. Government Accountability Office have each underscored in recent years the need for better attention to public infrastructure. A Congressional Budget Office report (pdf) released this week found that while federal investment in transportation is up, overall infrastructure spending (including things such as water and electricity systems) is down. And even with the recent bump in transportation spending, the Federal Highway Administration estimates that it would cost $9.4 billion annually over 20 years to eliminate that nation’s bridge deficiencies. And that’s just bridges.

Addressing national priorities should be one of the first considerations in any new legislation addressing infrastructure. But time and again, Congress has ignored the tough decisions in favor of special interest earmarks. Of course we don’t know the culprit that caused the Minneapolis bridge to collapse. But we do know that earmarking takes some of the decision-making authority away from engineers and puts it in the hands of lobbyists and lawmakers. And earmarking reduces the amount of federal dollars available for vital infrastructure investments and spreads the available transportation dollars so thinly that it reduces the impact of these new investments, rendering some of them useless.

When Congress gets back from its August recess, they will debate whether to raise the gas tax. Before that debate occurs, Congress should figure out how it’s going to better prioritize maintenance and upkeep. Simply throwing more money at the problem is likely to erode the public’s confidence that their hard earned dollars are really going to make roads and bridges safer and more reliable. Congress needs to learn that fixing infrastructure comes before funding political pork projects to nowhere.