Yesterday I put all of America's 600,000 bridges on a map with an eye toward visualizing the scope of what we fight about when we fight about American infrastructure. Today I want to dig a little deeper into the question and look at the condition of these bridges -- take a look at the map above (be sure to click for the huge version!). It shows the regions in the U.S. with the highest percentage of bridges deemed by the Federal Highway Administration as "structurally deficient."

Structural deficiency sounds scary, and it is, sort of. Deficient bridges are, broadly speaking, safe to drive across. In an interview last year with CBS, former Transportation Secretary Ray LaHood said that structurally deficient bridges "need to be really either replaced or repaired in a very dramatic way." He went on: "I don't want to say they're unsafe. But they're dangerous."

Not unsafe, but dangerous: that's the paradox of structural deficiency in a nutshell. When bridge engineers evaluate a bridge, they grade the condition of each of its major components -- its supports, the deck that vehicles travel across, etc. -- on a 0 to 9 scale. If any of these components receive a grade below a given threshold, the bridge is deemed structurally deficient. It needs some repair work to get back up to snuff.

Looking at the map above, it's immediately clear that some states have a bigger structural deficiency problem than others. Twenty two percent of Pennsylvania's 23,000 highway bridges are deficient, which, if you've ever had the misfortune of driving up I-81 in that state, you know in your heart to be true. Twenty one percent of Iowa's bridges don't make the grade. Same goes for 20 percent of South Dakota's, and 18 percent of Oklahoma's. These percentages are all considerably higher than the nationwide average of about 10 percent.

On the other hand, Nevada is doing the best job of keeping its bridges up to code -- fewer than 2 percent of that state's bridges are deficient. Likewise only 2 percent of Florida and Texas bridges are deemed deficient, and 3 percent of Arizona and Utah's.

Any number of factors contribute to this state-level variation. Weather and climate undoubtedly play a role -- Pennsylvania's winters, with constant freeze/thaw cycles, are a lot rougher on bridge materials than Nevada's. There may also be considerable difference in how these numbers are reported. Generally speaking, states are responsible for evaluating their bridges and reporting their condition to the FHA. Some states may be more frank in their assessments of bridge quality than others. Others are less diligent about sticking to the reporting schedule.

There's another measure of bridge quality that the FHA tracks, and that's "functional obsolescence." This sounds even scarier than structural deficiency, but is in many respects more benign. It simply means that a bridge was built to specifications that no longer meet modern requirements. It may be too narrow, or too light, or unable to deal with the heavier weights of today's vehicles. Obsolete bridges don't necessarily need to be repaired, but they do need to be replaced -- nobody wants to drive an 18-wheeler across a span built to accommodate Model Ts.

The geography of bridge obsolescence is distinct from the geography of deficiency. Obsolete bridges are strongly clustered in the Northeast, which makes sense: older cities = older bridges. More than a quarter of New York's bridges are obsolete, as are a third of Rhode Island's, 43 percent of Massachusetts', and a whopping 65 percent of DC's. Nationally, only about 14 percent of bridges are obsolete.

So you can start to see what's at stake when we talk about our bridge infrastructure. Overall, about one quarter of our nation's bridges are either obsolete or deficient. This means that roughly 1 out of every 4 bridges you drive over is in need of work done. The American Society of Civil Engineers -- who, let's face it, have a vested financial interest in making this work happen -- estimates that it would take a $20.5 billion annual investment to eliminate our deficient bridge backlog by 2028. And obsolete bridges are a different story. Barack Obama's recently-announced budget, containing $478 billion in highway funds, would go a long way toward plugging this gap.

To see where your state ranks on these measures, check out the table below.

State Total bridges Deficient bridges Obsolete bridges Percent deficient Percent obsolete
ALABAMA 16,088 1,388 2,144 8.63 13.33
ALASKA 1,544 153 198 9.91 12.82
ARIZONA 8,035 256 684 3.19 8.51
ARKANSAS 12,806 861 1,994 6.72 15.57
CALIFORNIA 25,406 2,501 4,306 9.84 16.95
COLORADO 8,668 529 859 6.10 9.91
CONNECTICUT 4,218 378 1,079 8.96 25.58
D.C. 253 14 164 5.53 64.82
DELAWARE 865 48 123 5.55 14.22
FLORIDA 12,137 243 1,760 2.00 14.50
GEORGIA 14,795 785 1,623 5.31 10.97
HAWAII 1,137 61 422 5.36 37.12
IDAHO 4,431 406 471 9.16 10.63
ILLINOIS 26,588 2,216 1,971 8.33 7.41
INDIANA 19,019 1,902 2,201 10.00 11.57
IOWA 24,300 5,022 1,183 20.67 4.87
KANSAS 25,085 2,416 1,813 9.63 7.23
KENTUCKY 14,194 1,191 3,253 8.39 22.92
LOUISIANA 12,982 1,837 1,944 14.15 14.97
MAINE 2,419 364 432 15.05 17.86
MARYLAND 5,305 317 1,104 5.98 20.81
MASSACHUSETTS 5,141 459 2,224 8.93 43.26
MICHIGAN 11,072 1,295 1,754 11.70 15.84
MINNESOTA 12,961 830 363 6.40 2.80
MISSISSIPPI 17,091 2,275 1,290 13.31 7.55
MISSOURI 24,385 3,310 3,145 13.57 12.90
MONTANA 5,251 400 514 7.62 9.79
NEBRASKA 15,374 2,654 986 17.26 6.41
NEVADA 1,898 34 215 1.79 11.33
NEW HAMPSHIRE 2,467 324 451 13.13 18.28
NEW JERSEY 6,609 621 1,722 9.40 26.06
NEW MEXICO 3,951 284 359 7.19 9.09
NEW YORK 17,456 2,012 4,733 11.53 27.11
NORTH CAROLINA 18,117 2,199 3,135 12.14 17.30
NORTH DAKOTA 4,429 701 243 15.83 5.49
OHIO 26,986 2,080 4,452 7.71 16.50
OKLAHOMA 23,147 4,216 1,575 18.21 6.80
OREGON 8,052 439 1,419 5.45 17.62
PENNSYLVANIA 22,691 5,050 4,388 22.26 19.34
RHODE ISLAND 766 174 255 22.72 33.29
SOUTH CAROLINA 9,338 1,031 891 11.04 9.54
SOUTH DAKOTA 5,872 1,174 238 19.99 4.05
TENNESSEE 20,077 1,083 2,863 5.39 14.26
TEXAS 52,937 1,127 8,872 2.13 16.76
UTAH 3,014 102 317 3.38 10.52
VERMONT 2,745 206 676 7.50 24.63
VIRGINIA 13,800 1,120 2,454 8.12 17.78
WASHINGTON 8,120 382 1,711 4.70 21.07
WEST VIRGINIA 7,187 960 1,541 13.36 21.44
WISCONSIN 14,109 1,212 759 8.59 5.38
WYOMING 3,127 422 284 13.50 9.08