The federal government's rating system for bridge safety tells us a lot, but not enough.

The eight-county Philadelphia region has 57 "structurally deficient" bridges with ratings as bad as, or worse than, the Minnesota bridge that collapsed on Aug. 1, killing 13 people. That tells us the costly scope of the repair job facing transportation officials in both Pennsylvania and New Jersey, as well as taxpayers who will foot the bill in those states.

But it doesn't tell drivers whether to avoid a certain bridge. Nor was the rating system intended for that purpose.

The doomed bridge in Minneapolis rated a 50 on a scale of 1 to 100. Many local bridges have much lower scores. For example, the DeKalb Pike bridge on Route 202 in Bridgeport scored only a 3. The northbound I-95 bridge over the Neshaminy Creek in Bristol Township rates a 5.

(One of the most famous bridges in the world, the Brooklyn Bridge, has a sufficiency rating of zero.)

Those lower-rated bridges are still standing, obviously, while the span in Minnesota crumbled. This illustrates that assessing the strength of bridges is an inexact science. And the Federal Highway Administration's rating system is an engineering classification, not a warning to drivers.

So if you choose to take the Betsy Ross Bridge instead of the Tacony-Palmyra because it's newer and looks to be in better condition, go ahead. But the scorecard is not a guarantee that one bridge is safer than another.

"Overall, motorists should feel confident that a bridge that's open is not going to fall down," said Greg Cohen, president of the American Highway Users Alliance, a nonprofit advocacy group based in Washington. Transportation officials, he said, need to make the bridge data more accessible and to explain better the consequences of delaying repairs.

PennDOT says if a bridge were unsafe, it would be closed. Nobody doubts the agency's commitment to protect the public. But the Minnesota example shows that tragic miscalculations can occur.

The Star-Tribune reported that Minnesota transportation officials talked openly about the possibility of the bridge's collapsing. In January, internal memos showed, those officials decided not to proceed with a $1.5 million repair job intended to reinforce beams in the span's critical section.

The real value of the bridge rating system is that it provides the public with a road map of future transportation policy.

For too long, state and federal governments have neglected bridge repairs. Pennsylvania has nearly 6,000 deficient bridges; New Jersey has about 750. Nationwide, there are more than 70,000 structurally deficient bridges. Repairing them will cost more than $9 billion per year for the next 20 years.

House Transportation Committee Chairman James Oberstar (D., Minn.) has called for a new trust fund, paid by a temporary gas-tax increase, to fix bridges in the national highway system. The panel's top Republican quickly dismissed the idea as a "Band-Aid."

However federal and state policy makers come up with the money, it's clear that the cost of postponing solutions - including more fatalities - is too high.

"We've got to be prepared to pay for it," Cohen said. "Our roads are reaching their midlife crisis."