Highway Accident Report

Adopted: November 7, 1989
COLLAPSE OF THE S.R. 675 BRIDGE SPANS
OVER THE POCOMOKE RIVER
NEAR POCOMOKE CITY, MARYLAND
AUGUST 17, 1988

NTSB Number: HAR-89/04
NTIS Number: PB89-916205


SYNOPSIS

On August 17, 1988, at about 1:00 a.m. e.d.t., a 85 foot section of the 275 foot long S.R. 675 bridge over the Pocomoke River fell about 30 feet into the river after two pile bents supporting the bridge collapsed. Witness reports indicated that the bridge may have been sagging before the collapse and no vehicles were involved in the collapse sequence. The weather was clear and dry, and water conditions were reported to be calm.

The National Transportation Safety Board determines that the probable cause of the collapse of the S.R. 675 bridge spans was the inadequate response of the Maryland State Highway Administration to deficiencies noted in the underwater bridge inspection reports. This resulted in the failure to repair or replace submerged untreated timber piles, which had deteriorated from the combined effects of bacteria, fungi, and aquatic insect larvae infestation, and abrasion by tidal currents. Contributing to the collapse was the improper batter of the timber piles and the preexisting cracks in the superstructure girders.

The primary safety issues raised by -this accident are the adequacy of the Maryland State Highway Administration (SHA) inspection and inspection report review procedures, the adequacy of SHA and Federal bridge load posting procedures, the adequacy of Federal requirements concerning the examination and testing of submerged timber piles, the adequacy of procedures concerning the identification and detection of bacteria, fungi, and aquatic insect larvae infestation of submerged timber piles, the use of untreated timber piles for bridge construction, and the identification of bridge deficiencies.

Safety Recommendations addressing these issues were made to the Maryland State Highway Administration, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the International Association of Chiefs of Police.

RECOMMENDATIONS

As a result of its investigation,, the National Transportation Safety Board recommends:

to the Maryland State Highway Administration:

Modify bridge inspection procedures to provide inspectors with “as built” plans if available, during on-site inspections. (Class II, Priority Action)(H-89-56)

Modify bridge inspection report review procedures to require reviewers to compare all inspection reports, design plans, and "as built” plans, if available. (Class II, Priority Action)(H-89-57)

Review the load rating calculations for all bridges within the State and consider the load carrying capacities of substructure members during the calculation process. (Class II, Priority Action)(H-89-58)

Reevaluate the load rating for bridges for which the substructure was not considered in load rating calculations. (Class II, Priority Action)(H-89-59)

During regularly scheduled underwater bridge inspections, require bridge inspectors to record at a minimum: incremental measurements of pile diameter, pile batter and direction, maximum ice pick penetration, and length of exposed piles. (Class II, Priority Action)(H-89-60)

Train, on comprehensive bridge inspection methods, State Highway Administration engineers who review bridge inspection reports and rate the bridges within Maryland. (Class II, Priority Action (H-89-61)

Provide the engineering staff in the SHA Bureau of Bridge Inspection and Remedial Engineering with sufficient capability to monitor the State underwater inspection program, the quality of reports and report reviews, the underwater inspection program for county and city bridges, and bridge maintenance, rehabilitation, and repairs. (Class II, Priority Action)(H-89-62)

Require when evaluating concrete bridges, that concrete core samples be six-inches or larger in diameter to improve the analysis of these structures. (Class II, Priority Action)(H-89-63)

Establish procedures for municipal governments to notify the SHA District Maintenance Office of any reported complaint concerning the condition of a bridge structure, and develop procedures to investigate all notifications thoroughly. (Class II, Priority Action)(H-89-64)

to the Federal Highway Administration:

Modify the Bridge Inspectors Training Manual to include information on the identification and detection of aquatic insect larvae infestation in submerged timber piles, the techniques for analyzing increment bore samples for bacteria, fungi, or other contaminants, and the need for sufficient measurements to enable complete assessment of the condition of timber piles. (Class II, Priority Action)(H-89-65)

Issue, as an interim measure, a technical advisory that discusses bacteria, fungi, and aquatic larvae infestation of submerged timber piles and the potential for cross sectional area loss of submerged timber piles as a result of these infestations. (Class II, Priority Action)(H-89-66)

Require State highway officials to include the condition of underwater bridge elements in load capacity calculations. (Class II, Priority Action)(H-89-67)

Develop guidelines and establish criteria, in cooperation with the American Association of State Highway and Transportation Officials, for testing timber increment bore samples to determine the presence of bacteria and decay fungi, and require that increment bore samples are retrieved during underwater inspections of bridges with submerged timber piles. (Class II, Priority Action)(H-89-68)

to the American Association of State Highway and Transportation Officials:

Modify the Standard Specifications for Highway Bridges, Section 4.3.2. entitled “Limitations on the Use of Untreated Timber Piles,” to preclude the use of untreated timber piles that are submerged in water. (Class II, Priority Action)(H-89-69)

Develop guidelines and establish criteria, in cooperation with the Federal Highway Administration, for testing timber increment bore samples to determine the presence of bacteria and decay fungi, and require that increment bore samples are retrieved during underwater inspections of bridges with submerged timber piles. (Class II, Priority Action)(H-89-70)

Modify Section 2.4.2, "bents", of the Manual for Maintenance Inspection of Bridges to include information on how to identify and detect aquatic insect larvae infestation in submerged timber piles. (Class II, Priority Action)(H-89-71)

Modify Section 4.5, "Rating of Bridges, Evaluations" to require the evaluation of substructural bridge members during load rating calculations. (Class II, Priority Action)(H-89-72)

Modify Section 5.2.2, “Live Loads,” of the Manual to require that computations for stresses and allowable loads consider at least one maximum loaded vehicle in each bridge lane. (Class II, Priority Action)(H-89-73)

Advise State highway officials to obtain water quality data from State environmental agencies, especially concerning locations where concentrations of aquatic insect larvae have been found, and evaluate this data in conjunction with scheduled underwater bridge inspections. (Class II, Priority Action)(H-89-74)

International Association of Chiefs of Police:

Advise your members of the circumstances of the S.R. 675 (Pocomoke City) bridge collapse, and urge them to notify state transportation officials when a complaint is received concerning a bridge. (Class II, Priority Action)(H-89-75)