The collapse of the Interstate-35W bridge over the Mississippi River in Minnesota on August 1 that took the lives of 13 people and injured many others has raised questions about the safety of the more than a half-million bridges throughout the United States, including over 17,000 bridges in New England.
A steel arch deck truss structure, the Minnesota span was classified "structurally deficient" in 1990, a category shared by 12 percent, or 73,518, of America's 594,709 bridges. Similarly, approximately 13 percent, or 2,224, of New England's 17,315 bridges are so classified. (See accompanying table on New England Bridge Conditions).
In addition, about 13 percent, or 80,226 of U.S. bridges, are categorized "functionally obsolete." In New England the figure is much higher — nearly 27 percent, or 4,668 of our bridges fall in that category.
Neither type of deficiency indicates that a bridge is unsafe. According to the U.S. Department of Transportation, structurally deficient means there are elements of the bridge that need to be monitored and/or repaired. The fact that a bridge is "deficient" does not imply that it is likely to collapse or that it is unsafe. It means they must be monitored, inspected and maintained.
Most structurally deficient bridges are left open to traffic while they undergo maintenance and repair. If inspectors find unsafe conditions they restrict access or close the bridge, says USDOT. Nothing in the inspection reports indicated that it was necessary to limit access or close the I-35W bridge.
In contrast, a functionally obsolete bridge has geometrics not meeting current design standards — it may be too narrow, have inadequate under-clearance, or for some reason other than deterioration, simply cannot meet today's service standards.
Generally, rural bridges tend to have a higher percentage of structural deficiencies, while urban bridges have a higher incidence of functional obsolescence due to rising traffic volumes.
Bridge inspectors follow strict guidelines called The National Bridge Inspection Standards (NBIS). In place since the early 1970s, these require biennial safety inspections for bridges over 20 feet long on public roads. The inspectors ensure safety through hands-on inspections and rating of components, such as deck, superstructure and substructure. This composition and condition information is maintained in the national bridge inventory (NBI) database, maintained by the Federal Highway Administration (FHWA).
Under the guidelines some structures can be inspected every four years if they are considered to be in very good condition. About 83 percent of bridges are inspected once every two years, 12 percent are inspected annually, and 5 percent are inspected on a four-year cycle. Structures with "fracture critical members" — components that are in tension whose failure would probably cause a portion of, or the entire, bridge to collapse, are not eligible for the four-year inspection cycle. Gusset plates, which connect steel members in a frame or a truss, are considered fraction critical members.
Most bridges in New England are inspected at least every two years. In New Hampshire, however, the state's Department of Transportation maintains a "Red List" of 140 bridges with such low Federal Sufficiency Ratings (FSR) due to poor conditions, weight restrictions or type of construction, that they must undergo two inspections each year. FSR values run from 0 to 100 — the lower the number the poorer the condition of the structure.
While federal and state officials haven't yet determined the cause of the I-35W bridge failure, U.S. Secretary of Transportation Mary E. Peters recently called on all states to immediately inspect any steel deck truss bridges similar to the Minnesota span. According to FHWA data, there are 756 of the relatively unique steel deck truss bridges in the United States, including 42 located in New England.
She also cautioned states to carefully consider the additional weight placed on bridges during construction or repair projects. The National Transportation Safety Board (NTSB) has indicated that the stress on the gusset plates may have been a factor in the collapse of the Minnesota span, and that one possible stress may be the weight of construction equipment and materials on the bridge.
The collapse of the I-35W bridge has focused attention on America's aging infrastructure, and has sparked politicians' demands for raising taxes to pay for repairs. But there are two sides to this political hot potato. On the one hand, groups such as the American Society of Civil Engineers (ASCE), the Road Information Program (TRIP) and the American Road and Transportation Builders Association (ARTBA) are in support of raising taxes for repairing infrastructure, while several taxpayers groups are adamantly opposed.
A case in point: On August 8 ARTBA applauded House Transportation and Infrastructure Committee Chairman Jim Oberstar (D-Minn.) for an initiative he announced to quickly address America's bridge problem that may involve raising taxes on gasoline and diesel fuel.
"Chairman Jim Oberstar today displayed the political leadership and 'can do' attitude that are key to beginning the hard task of seriously addressing America's national transportation system deficiencies," said ARTBA President & CEO Pete Ruane.
"The federal surface transportation investment program needs to change to meet the demands and challenges of this century, not the last one. We believe the Oberstar bridge proposal signals a necessary first step toward legislatively refocusing and reinvigorating it.
"The approach he has outlined is not Washington 'business as usual.' It is a strategic, targeted capital investment plan that has accountability and a defined national outcome — eliminating structurally deficient bridges on America's most heavily traveled highways."
On the other side of this issue is the Citizens Against Government Waste (CAGW), which believes a tax increase is not necessary if Congress spends the money it already receives more wisely.
The non-profit, non-partisan group named Rep. Oberstar "Porker of the Month" for August 2007. CAGW said that in the wake of the bridge collapse in the congressman's home state in which at least nine people were killed, Chairman Oberstar's immediate reaction was to propose a "temporary" 5-cent increase in the gas tax to raise $25 billion within three years for a new bridge trust fund.
CAGW pointed out that "the 2005 highway bill contained $2 billion annually for bridge reconstruction. During its markup of the bill, the House Transportation Committee considered increasing that figure to $3 billion a year. The committee not only failed to include the higher level of bridge repair funding, it opened the door for members of Congress to stuff the bill with nearly 6,500 pork-barrel projects worth more than $24 billion, about the same amount now being sought by Rep. Oberstar with his proposed tax increase."
A table prepared by CAGW shows that 79,079 "earmark projects" (pork-barrel) were slipped into appropriations bills between 1991 and 2007, costing taxpayers $253.5 billion. Pork projects are defined as meeting at least one of CAGW's seven criteria, but most satisfy at least two:
- Requested by only one chamber of Congress
- Not specifically authorized
- Not competitively awarded
- Not requested by the president
- Greatly exceeds the president's budget request or the previous year's funding
- Not the subject of congressional hearings
- Serves only a local or special interest
In reporting on a proposed gas tax increase in its August 18 edition, The Wall Street Journal noted that the levy is supported by a coalition of road builders, environmentalists, economists, and even former federal reserve Chairman Alan Greenspan. But it also reported that a survey of 500 adults in Minnesota found that, even after the collapse of the I-35W bridge, only 30 percent would support an increase in the federal gas tax to fund infrastructure improvements, while 62 percent were opposed. (Current gasoline and diesel fuel taxes for the New England states are shown in the accompanying table.)
President Bush is likewise opposed to a tax increase. In commenting on politicians who want to raise taxes, he said, "Before we raise taxes which could affect economic growth, I would strongly urge the Congress to examine how they set priorities. And if bridges are a priority, let's make sure we set that priority first and foremost before we raise taxes."
|Connecticut||Maine||Massachusetts||New Hampshire||Rhode Island||Vermont||Total|
|# of Bridges||4,166||2,380||4,947||2,359||753||2,710||17,315|
|#of Structurally Deficient||351||343||586||317||191||436||2,224|
|#of Functionally Obsolete||1,050||477||1,974||431||234||502||4,668|
|Percent of Bridges — Structurally Deficient||8%||14%||12%||13%||25%||16%||12.8%|
|Percent of Bridges — Functionally Obsolete||25%||20%||40%||18%||31%||19%||26.9%|
|# of Steel Deck Truss Bridges||6||6||19||3||0||8||42|
|State||Total State & Federal||Total State & Federal|
|*Federal Gasoline Tax = 18.4 cents/gallon
**Federal Diesel Tax = 24.4 cents/gallon