the most heavily trafficked train bridge in the USA is 105 years old, and a $900 million dollar problem, as it's near it's end of life

 Portal Bridge in New Jersey. Photo by Bloomberg

Designed in the 1840s and completed in 1910, this bridge is, as the New York Times put it last year, a "$900 million problem." Everyday it withstands a beating from nearly 500 trains, more than any other bridge in the Western Hemisphere. It's also a swing bridge, which means it has to be opened regularly so barges can pass through the river, causing delays along Amtrak's Northeast Corridor when it fails to lock back properly.

It carries more passenger trains than any other railroad bridge in the Western Hemisphere, yet few people beyond those who rely on it have heard of it. It goes largely unnoticed, unless something goes wrong, which happens with irritating frequency. After all, the bridge is 104 years old.

Every time it swings open to let a boat pass is a test of early-20th-century technology that can snarl train travel from Boston to Washington, the nation’s busiest rail corridor. And over the years, because it is partially made out of wood, it also has proved to be quite flammable.

From Jan 2013 to Sept 2014 it caused 250 delays according to New Jersey Transit, it's biggest user.
For something built in 1910, Mr. Galloway said, “structurally, it probably is in reasonable condition.” But, he added, its mechanical and electrical systems are “reaching the end of their useful lives.” 

Indeed, the bridge, expected to last 100 years, is swinging on borrowed time.

http://www.vice.com/read/america-is-collapsing-a-brief-look-at-the-us-infrastructure-meltdown-130?utm_source=vicefbus
http://www.nytimes.com/2014/09/26/nyregion/portal-bridge-presents-northeast-rail-commuters-with-a-104-year-old-problem.html?_r=0

But that's not the worst or most expensive problem... just the ones with the most New Yorkers inconvenienced.

The bridge that looks to cost the most money, and isn't going to get funded because the bill is too high?

Is the Brent Spence Bridge over the Ohio River, the I 71 / 75 from Ohio to Kentucky. They expect it will cost 2 and a 1/2 billion to fix. Neither state is stepping up or willing to shoulder 1/2 the cost. I think they are going to wait until the feds jump in.

It was built in 1963, declared obsolete in 1998, and only the taxpaying population of commuters and truckers are inconvenienced, because politicians don't drive... unless its a parade.