Not surprisingly, the collapse of a bridge along Interstate 5 in Washington state yesterday has revived the long-standing debate over whether Congress should spend more to repair the nation's aging roads and bridges.

It's worth being very clear upfront that the I-5 bridge in question wasn't considered "structurally deficient" in any way — the bridge collapse is being blamed on a truck bumping an overhead girder.  All we do know is that the bridge was sort of old. (Fortunately, no one died or was seriously injured.)

Here's the AP: "The bridge was built in 1955 and has a sufficiency rating of 57.4 out of 100. That is well below the statewide average rating of 80 ... but 759 bridges in the state have a lower sufficiency score." The bridge was also classified as "functionally obsolete," but that doesn't mean it was unsafe, just that it was built according to earlier standards.

That said, infrastructure spending is in the news again, so here are a few ways to think about the topic. Joe Wiesenthal created this chart to show that U.S. public construction spending as a percentage of GDP has dropped to its lowest point in 20 years, after a big uptick before the recession:

Now, that's a chart of all public construction spending, from highways to water projects to public hospitals to schools. So what if we just look at highways and roads? We get this chart:

There's still been a big drop-off in recent years, although that also came after a big build-up in the late 2000s. (Sadly, the data series doesn't extend back before 2002, so it's tough to see what this looks like historically.)

How did this happen? States and local governments are the biggest part of the story here. They've historically provided the vast majority of spending for roads, highways and bridges, and they've been pulling back on spending since 2008 as a result of the economic downturn and requirements to balance their budgets. California’s transportation spending declined by 31 percent from 2007 to 2009, for instance. Texas's fell by 8 percent.

At the same time, Congress hasn't filled in the gap. There was a one-time $46 billion infusion of transportation spending in the stimulus bill. But that wasn't enough to offset the  drop at the state and local level. Meanwhile, the most recent highway bill out of Congress kept federal spending at current levels rather than increasing it.

The big question is whether Congress should be spending more — and if so, how much? We've seen various reports arguing that America's infrastructure is in dire need of an upgrade. The American Society of Civil Engineers gave the nation's bridges a C+ in its 2013 report card, and said that full repairs would cost $20 billion per year over the next decade, a 60 percent boost in spending. These estimates don't always take a full account of costs and benefits, but the I-5 collapse will no doubt give these groups more ammo.

Another consideration, meanwhile, is that Congress can borrow money for remarkably low rates right now. And experts say it's typically cheaper to fix roads and bridges early on rather than wait until they get truly decrepit. That suggests now could be an apt time to invest in repairs, rather than putting them off until later.