Iowa Bridges Ranked Fourth Most Deficient In The Nation

Staff -- Associated Construction Publications, 2/21/2008

Iowa has the fourth highest percentage of structurally deficient bridges in the nation, with more than one-fifth of the state’s bridges in need of immediate repair or replacement because of deterioration, according to a new report released today by TRIP, a national nonprofit transportation research group based in Washington, D.C.

According to the TRIP report, twenty-one percent of Iowa’s bridges are structurally deficient, showing significant deterioration to decks or other major components. An additional six percent of the state’s bridges are rated as functionally obsolete because they no longer meet current design and safety standards.

With current funding, the Iowa Department of Transportation (IDOT) is able to significantly repair or replace an average of 20 bridges annually. However, the number of bridges annually repaired or replaced will drop to just 15 in 2008. IDOT estimates that, on average, between 20 and 30 state-maintained bridges become structurally deficient each year.

Included in the report is a list of the 100 state-maintained bridges in Iowa (carrying at least 2,500 vehicles per day) that have the lowest rating based on condition, design and traffic volume. Individual components of the bridge are rated on a scale from 0-9 with those scores figuring into the overall rating. Typically, the deck of a bridge, the superstructure and the substructure are rated based on their physical condition, with 0 being the worst rating. The full scale is included in the report.

The following are the top ten of the 100 lowest rated state-maintained bridges in Iowa.

	Route Carried	County	Route or feature intersected	Average Daily Traffic	Year built	Composite Rating	Deck Rating	Superstructure Rating	Substructure Rating
1	30	Tama	Small Natural Stream	4,350	1951	3	3	3	5
2	65	Hardin	Iowa River	9,700	1928	4	4	3	4
3	6	Iowa	Small Natural Stream	3,320	1929	7	5	6	4
4	63	Lyon	Over Up RR	3,490	1936	7	4	3	4
5	29	Pottawattamie	Honey Creek	21,200	1958	7	6	3	4
6	29	Pottawattamie	Honey Creek	21,200	1958	8	6	3	4
7	169	Kossuth	E Fork Des Moines River	9,700	1954	10	5	4	6
8	92	Pottawattamie	Middle Silver Creek	5,800	1953	15	5	4	4
9	12	Woodbury	Over RR, RVR, STS	26,400	1936	17	4	5	5
10	12	Woodbury	Over Abandoned RR	13,200	1954	17	3	5	4

A significant number of state maintained Iowa bridges are close to becoming structurally deficient if needed repairs are not made. According to IDOT calculations, 622 state-maintained bridges have a deck, superstructure or substructure rating of five, which is within one point of being classified as structurally deficient.

“Iowa’s bridges are aging and overburdened, at a time when the state is unable to fund all needed bridge repairs. Additional funding for needed improvements could prevent Iowa’s already deteriorated bridges from worsening,” said William M. Wilkins, TRIP’s executive director.

The TRIP report suggests several strategies for improving bridge conditions in Iowa. These strategies include increasing bridge investment statewide to allow for an expanded program of bridge repairs, expanding the current bridge maintenance program to slow the rate of deterioration, and using high-performance materials when building or reconstructing bridges.

Additional findings of the TRIP report include:

A bridge is structurally deficient if there is significant deterioration of the bridge deck, supports or other major components. Bridges that are structurally deficient are often restricted to carrying lower weight vehicles or are closed if they are found to be unsafe.
The classification of a bridge as "structurally deficient" does not mean the structure is unsafe. Iowa’s bridge safety inspection program ensures that each bridge is safe for vehicles weighing less than the posted weight limit. If the inspection determines a bridge to be unsafe for cars, the bridge is closed until repaired or replaced.
Functionally obsolete bridges are not automatically rated as structurally deficient, nor are they inherently unsafe. Functionally obsolete bridges are those that do not have adequate lane widths, shoulder widths, or vertical clearances to serve current traffic demand.