Performance

Infrastructure condition

Iowa Bridge Condition Index

The Iowa Bridge Condition Index reflects the overall condition of the bridge, taking into account things such as structural condition, load carrying capacity, horizontal and vertical clearances, width, traffic levels, type of roadway it serves, and the length of out-of-distance travel if the bridge were closed. A bridge in good condition is adequate for today's traffic and vehicle loads. A bridge with a poor condition index rating is not unsafe, but should be considered for repair, replacement, restriction posting, weight limits, or monitoring on a more frequent basis.

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Displayed data: Includes bridges on all public roads in Iowa, regardless of jurisdiction – interstate, U.S., Iowa, county, municipal, etc.

Trends in Iowa highway bridge data

Across the United States, bridges are rated using a standard methodology defined by the Federal Highway Administration and reported in the National Bridge Inventory (NBI). The following data and definitions follow these federal standards.



Functionally obsolete

Bridges where the geometrics of the bridge in relation to the geometrics required by current design standards are not met. Functional obsolescence results from changing traffic demands on the structure. Bridges are designed to conform to the design standards in place at the time they are designed. Over time, improvements are made to the design requirements. The magnitude of these types of deficiencies determines whether the existing conditions cause the bridge to be classified as functionally obsolete.




Displayed data: Includes only bridges on primary routes – interstate, U.S., and Iowa routes. County and city bridges are not included.

Structurally deficient

Bridges where significant load carrying elements are found to be in poor or worse condition due to deterioration and/or damage, or the adequacy of the waterway opening provided by the bridge is determined to be extremely insufficient to the point of causing intolerable traffic interruptions. The fact that a bridge is "deficient" does not immediately imply that it is likely to collapse or that it is unsafe. If a bridge is determined to be unsafe, the structure must be closed. A "deficient" bridge, when left open to traffic, typically requires significant maintenance and repair to remain in service and eventual rehabilitation or replacement to address deficiencies. In order to remain in service, structurally deficient bridges are often posted with weight limits to restrict the gross weight of vehicles using the bridges to less than the maximum weight typically allowed by statute.


Displayed data: Includes only bridges on primary routes – interstate, U.S., and Iowa routes. County and city bridges are not included. </h3">
Pavement smoothness

One indicator of pavement condition is the smoothness of the ride. This measure gets to the subjective "feel" of the roads that most of us notice when we’re riding on the road. Although this can vary by season, due to Iowa’s climate roads are typically rougher in the winter, the measure of smoothness is one indicator of the overall pavement health – particularly when combined with measures of pavement structure.

All states use a federally mandated standard measure of pavement smoothness, the International Roughness Index (IRI). The map below classifies each of Iowa’s primary routes as good, fair, or poor based on pavement smoothness. It is important to note that this is only one indicator of overall pavement condition and many other factors are also taken into consideration when determining which roads are candidates for rehabilitation.



Displayed data: Pavement smoothness for all primary highways in Iowa (numbered interstate, U.S., and Iowa routes).