Our Opinion: What do bridge rankings mean for travelers?

"Critical' has an ominous sound when applied to the condition of a bridge motorists cross every day.

A total of 641 Missouri bridges, including 50 in 10 Central Missouri counties, now are on the critical list, according to the Missouri Department of Transportation. And the statewide total has increased from the 591 in 2014.

From a safety standpoint, motorists have no need to worry.

Dennis Heckman, MoDOT's bridge engineer, explained critical does not mean unsafe. "When we discover a problem that is a safety issue," he said, "we close the bridge."

Tuesday's News Tribune story on the new rankings was headlined: "Area bridges on "critical' list." MoDOT's detractors will say the emphasis is designed to drum up support for a tax proposal. MoDOT supporters will counter that the rankings reflect real infrastructure problems that must be addressed with added revenue.

So what do these rating and rankings mean to travelers?

Bridges are rated according to National Bridge Inspection Standards. In Missouri, Heckman said, the scale ranges from 9, excellent, to 2, closed. Critical bridges are rated 3 or 4, only a step or two away from being closed, according to Heckman. Those bridges must be inspected each year.

Bridges rating 4 or less are classified as structurally deficient. Some older bridges not built to current standards are classified as functionally obsolete. Neither classification means a bridge is unsafe.

In addition to bridges ranked critical, MoDOT's bridge inspectors examine about half of the state's 10,400 bridges annually.

Bridges are rated on three criteria. They are:

• Deck, which includes the surface.

• Superstructure, including primary load-carrying members and connections.

• Substructure, which includes the abutments and piers.

The lowest of the three ratings is the overall rating of the bridge.

Heckman said some bridge repairs can be done with available MoDOT staff, resources and funding. In other cases, however, weight limits must be imposed.

Tighter weight limits, he added, may prohibit bridge crossings by school buses, fire trucks, ambulances and snow plows.

The increase in critical bridges may not constitute an immediate safety issue, but it indicates that segment of the state's infrastructure is deteriorating.

Missourians must decide if, and how, they intend to address those deficiencies.