Where are the Dangerous Locations for the Next Minneapolis Bridge Collapse

One of the natural questions to follow a tragic event like the I 35W Minneapolis bridge collapse is where are there other bridges that could suffer a similar fate. In our last post we talked about the National Bridge Inventory, the valuable information contained in it, and the difficulty working with it.

My original hope was to load up a dataset with lat longs for the dangerous bridges across the country, but after Raj spent many hours trying to sort out the geo-coding inaccuracies in the data set it became apparent that would not be possible. The latitude and longitude coordinates simply did not map to reality, the entire state of New Jersey was missing coordinates, and many time the last two digits of resolution were zeroed out. So, Raj aggregated the data to the next best level of resolution – counties. The bad news is you cannot tell where in that county the dangerous bridges are, but you can tell which counties have the riskiest bridges and if it is one you drive through. We are still working on trying to derive a finer grain picture and will definitely post those up if we can come up with something accurate.

Where are the the most dangerous bridges:

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The top 5 most dangerous counties and the total number of dangerous bridges are:

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Garfield Oklahoma 78

Attala Mississippi 45

Allegheny Pennsylvania 42

Washington Pennsylvania 37

Montgomery Pennsylvania 36

So, how was this all calculated? First we took the National Bridge Inventory and grabbed the safety ratings for all bridge’s superstructure, substructure, and decks (found here):

“The NBI database contains ratings on the three primary components of a bridge: the deck, superstructure, and substructure. A bridge deck is the primary surface used for transportation. The deck is supported by the superstructure. This transfers the load of the deck and the traffic carried to the supports. Within the superstructure are the girders, stringers, and other structural elements. The substructure is the foundation of the bridge and transfers the loads of the structure to the ground. The superstructure is supported by the substructure elements, such as the abutments and piers.”

For each of the key bridge components, decks, superstructure, and substructure we provided counts by county for the number of bridges by their safety ratings (ranging from “failed” to “excellent”). We also created three indexes: 1) dangerous bridges (the sum of the number of failed, imminent, critical, and serious bridges), 2) risky bridges (the sum of the number of poor, fair, and satisfactory bridges) and 3) safe bridges (the sum of the number of good, very good, and excellent bridges).

The embedded map show the number of dangerous bridges rated by their superstructure. In the Minneapolis bridge collapse the superstructure was rated “poor” and all the bridges mapped are bridges in worse condition by safety rating. This is just one slice of the data. The best way to see how your location rates is to head to GeoCommons and create a map by clicking the “mymaps” tab and adding one of the three datasets. Just search “bridges” or by type “superstructure”, “substructure”, “decks”. Once you’ve made the map you can also click on the “about this dataset” link and create top ten lists for whatever data attribute you think is most critical. We hope this allows a mechanism for the public to discover if there are dangerous bridges in their backyard.