Chapter 8.2, Problem 95E

To determine

To work: an extended application analyzing the numbers of structurally deficient bridges in the united states from 2001 through 2017.

Explanation of Solution

Bridges are an integral part of the U.S. highway network, providing links across natural barriers, passage over railroads and highways, and freeway connections. The Federal Highway Administration (FHWA) maintains a database of our nation's highway bridges—the National Bridge Inventory (NBI)—with detailed information on all public road bridges greater than 20 feet. This special report gives a brief synopsis of that inventory, including bridge condition and the resources spent for maintenance and upgrades.

Of the 612,408 highway bridges reported, 54,254 (8.86 percent) were rated deficient for 2017. August 22, 2019

Federal law mandates the uniform inspection of all bridges for structural and functional adequacy at least every two years; bridges rated “deficient” are eligible for federal repair dollars. The National Bridge Inventory (NBI) is the source of the bridge data below, although we also use summaries provided in Better Roads (see Appendix). Since the NBI contains some recent inspections and some as old as two years, the age of the “average” inspection is about one year old. So, a “December 2017” summary from the NBI would represent, on average, bridge condition as of 2016.

This year’s ranking measures structurally deficient bridges (those with deteriorated conditions that need maintenance in the near future to ensure continued safety) but not functionally obsolete ones (those that have narrower lanes or shoulders but no structural concerns). While neither condition is ideal, structurally deficient bridges are a much bigger problem. Functionally obsolete bridges are older and built to different design standards and tend to be located in states with more mature infrastructure.

The condition of the nation’s highway bridges in 2017 improved slightly from 2015, the last time this assessment was completed. Of the 612,408 highway bridges reported, 54,254 (8.86 percent) were rated deficient for 2017 (Table 16, Percent of Structurally Deficient Bridges, 2017, Figure 11). This represents a 0.74 percent improvement over 2015 when 58,485 of 609,285 (9.60 percent) were rated as deficient.

Two states reported less than 2 percent of their bridges to be structurally deficient: Texas and Nevada at 1.57 percent and 1.59 percent respectively. Two states reported more than 20 percent of their bridges as structurally deficient: Rhode Island and Iowa, at 23.26 percent and 20.93 percent respectively. The majority of states (39) reported at least some improvement in the percentage of structurally deficient bridges between 2015 and 2017, with Pennsylvania, Oklahoma and Wyoming seeing the most improvement (2.7, 2.4 and 2.1 percentage points, respectively). Of the 11 states that reported a higher percentage of deficient bridges, two saw increases of more than one percentage point: West Virginia at 3.85 percent and Montana at 1.87 percent.