Structurally deficient bridge report by ARTBA

By degree of bridge-structural-deficiency: Yellow 0-4.9% of state bridges, Orange 5-8.9% of state bridges, Red 9% or higher of state bridges

(Courtesy ARTBA)

Nine percent of bridges in Massachusetts, 483 of the total 5,171 bridges, are structurally deficient, according to a 2017 report by non-partisan transportation research group the American Road and Transportation Builders Association.

Massachusetts ranks 31st on the list for most number of structurally deficient bridges in 2016, which the report amasses to 56,000 nationwide. The ARTBA defines a deficiency as "poor" or "worse condition" for various parts of the bridge, such as the deck or substructures. Iowa tops out with the highest number of unsound bridges, 4,968 of 24,184, while Nevada came in last with only 31 deficiencies among its 1,933 bridges.

In the bay state, 43 percent of all bridges are classified as "functionally obsolete," which means the bridge's design does not meet standards used to build bridges today.

The report lists the most-traveled structurally deficient bridges. Here are the top five:

201,000 drivers travel

172,000 drivers travel

159,900 drivers travel

154,500 drivers travel

138,689 drivers travel

ARTBA reports that Massachusetts has identified needed repairs on 4,699 bridges (not all of which are structurally deficient), which the state estimates would cost $19 billion.

The report's analysis uses bridge data from files published in January by the Federal Highway Administration, an arm of the U.S. Department of Transportation.