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How studied bridge inspections

How studied bridge inspections.'s Bill Dedman reports.
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Here’s how studied the state of bridge inspections around the country.

We used federal records to calculate whether each bridge had been inspected within 24 months. We also calculated separately whether each bridge was overdue under the timetable for that particular bridge.

In making our calculations, we were careful to give the benefit of the doubt to the states.

Source of the records
Federal regulations require that bridges of at least 20 feet that carry vehicular traffic on a public road must be inspected at least every 24 months, unless the state or federal agency that owns the bridge gets a special exemption. Only bridges in sound condition are eligible for such exemptions. For bridges in poor condition, states can set stricter schedules.

Every spring, states submit inspection records from the previous year to the Federal Highway Administration, which uses the data to distribute money for repair of highways and bridges. The inspection records are stored in a database called the National Bridge Inventory.

After the Minneapolis Interstate 35 bridge collapsed in August, many news organizations used an earlier version of this database to describe the condition of the nation's bridges.

The file, however, was a year out of date. It included inspections only through 2005 for most states, as submitted in April 2006. asked the Federal Highway Administration for a new file, showing the inspections through 2006, as submitted in April 2007.

At first, the highway administration denied our request, saying that its practice was to wait until the following year to release the database. argued that the database was a public record under the federal Freedom of Information Act. The highway administration relented on Sept. 17, posting the new data file online where anyone could see it. This is the first report based on those records.

The analysis
Nearly 600,000 bridges are listed in the National Bridge Inventory. They carry traffic over rivers, streams, highway overpasses, railroads and other obstructions.

One state, Kentucky, didn't send in its records in 2007, so we couldn't calculate how many of its bridges were inspected on time.

But for the rest of the nation, we have two pieces of information: the number of months between required inspections, and the month of its last inspection. If the bridge was on a 24-month schedule, and it had been inspected within 24 months, we called it on time. If it had been longer than 24 months, it was overdue.

The complication: Bridge owners are allowed some time for data entry. The federal regulations allow up to 90 days to enter the data, if bridges are owned by state or federal agencies, and 180 days for other bridges, such as those owned by counties and towns.

We didn't want to call a bridge overdue if in fact it had been inspected on time but the data just hadn't been entered. So we gave the full time allowed for data entry under the regulations, and an extra month for good measure.

To give every benefit of the doubt, we assumed that state and federal bridge had been inspected on Dec. 1, 2006. That gave the states a cushion: four full months to get the data entered before the April 1 deadline.

For example, in the case of a state bridge on a 24-month schedule:

  • If the database shows its last inspection in December 2004, then it was due for re-inspection in December 2006. We assume it got that inspection, and therefore we listed it as on time.
  • If the database shows its last inspection in November 2004, then it was due for re-inspection in November 2006. Because no re-inspection was reported, it was overdue by one month.

Local bridges get six months for data entry, so we assumed that they all were inspected on Sept. 1, 2006. That gave them a cushion: seven full months before the April 1 deadline.

That’s why we say that "at least" 17,000 bridges didn't get their two-year inspection, because it's not likely that every bridge really did get inspected the day after the database cutoff.

Some records not included
Sometimes states submitted contradictory records. For example, a bridge might be listed as carrying a road, but also listed as having only pedestrian traffic.

And some states submit too many records, such as bridges too short to be covered by the inspection regulations.

We took the most conservative route, excluding any bridge that met any one of these conditions:

  • No road on the bridge.
  • Closed to traffic.
  • 20 feet or less in length.
  • Pedestrian or rail bridges.
  • Number of lanes listed as 0.
  • Privately owned bridges (other than those owned by railroads), or owner listed as unknown.
  • Border bridges where the neighboring state has more than half the responsibility for maintaining the bridge.

That left 592,000 bridges to be studied.

Separate calculations for 'late' and 'past 24 months'
States can get federal permission to put some low-risk bridges on longer schedules, and may choose to put high-risk bridges on shorter schedules. Most notable is Ohio, which by law puts every bridge on a 12-month schedule. (That pushes up the rate of overdue bridges in Ohio, because it sets a higher bar.) Other states generally set short schedules only for bridges in poor condition.

Because of the federal exemptions, in addition to calculating how many bridges went past 24 months since their last inspection, also calculated which bridges were late for their inspection, judging them by the schedules that each state set for individual bridges. Of course, in a state that puts no bridges on long schedules, the calculations would work out about the same.

The records show that at least 11,714 bridges were late for their inspection, or 2 percent of the total. That's lower than the number that had gone more than two years since their last inspection: 17,218, or 3 percent.

Only four states had no bridges that were late for their inspection: Georgia, Nevada, Tennessee and Virginia. And a slightly different group of four states had no bridges that went past 24 months: Delaware, Georgia, Nevada and Tennessee.

The worst on-time rates, judging bridges by their individual schedules, were in these states: Hawaii (at least 46.5 percent), Rhode Island (27.5 percent), D.C. (11.5 percent), Alaska (8.1 percent), Arizona (7.6 percent), and Ohio (7.5 percent). When judged by bridges going past 24 months, the worst rates were in Hawaii (46.5 percent), Rhode Island (27.5 percent), Arizona (26.7 percent), New Mexico (17.4 percent), and West Virginia (12.2 percent).

Counties and towns owned the greatest number of bridges that were late (5,246), followed by states (3,291) and federal agencies (2,893). When judged by bridges going past 24 months, states owned the most (7,961), followed by cities and towns (6,276), and federal agencies (2,939).

On interstate highways, 630 bridges were late for inspection, or 1.1 percent of the nation's freeway bridges. And 1,556 went more than 24 months, or 2.8 percent.

Filling out the forms
Massachusetts highway officials didn't fill out the forms in the same way that other states do. Instead of filling in the schedule for inspection of a bridge (almost always 24 months in Massachusetts), the state highway department said it filled in a much lower number, making about 200 bridges look late for inspection, though they really were not.

We worked with the state to set the right inspection frequency for the bridges. Nearly all were set at 24 months.

Bottom line: Only three bridges in Massachusetts were overdue for inspection.

State-by-state files are available is making available state-by-state files of all bridges in the nation, including inspection dates and condition ratings. To receive those files in Excel format, send a request to