Highway Accident Report

Adopted: June 5, 1990
APRIL 1, 1989

NTSB Number: HAR-90/01
NTIS Number: PB90-916201


About 8:15 p.m. c.s.t., April 1, 1989, an 85.5-foot-section of the 4,201-foot-long northbound U.S. Route 51 bridge over the Hatchie River fell about 20 feet into the 24-foot deep rain-swollen river after 2 pile supported column bents supporting 3 bridge spans collapsed. Witness reports and physical evidence indicate that the southern column (70) bent and the two spans that it supported fell quickly causing 4 passenger cars and 1 tractor-semitrailer to plunge into the river. The adjacent column bent (71) and the span that it was supporting, then collapsed on top of the vehicles. The river had apparently been at flood stage since November 1988. All eight vehicle occupants died as a result of the collapse.

The National Transportation Safety Board determines that the probable cause of the collapse of the northbound U.S. Route 51 Bridge spans was the northward migration of the main river channel which the Tennessee Department of transportation failed to evaluate and correct. Contributing to the severity of the accident was the lack of redundancy in the design of the bridge spans.

The primary safety issues raised by this accident are the adequacy of the Tennessee Department of Transportation (TDOT) inspection and inspection report review procedures; the adequacy of TDOT bridge maintenance guidelines; the adequacy of TDOT overweight vehicle permit procedures; and the adequacy of Federal guidelines and standards for highway bridge inspection.

Safety Recommendations addressing these issues were made to the Federal Highway Administration, the American Association of State Highway and Transportation Officials, the Tennessee Department of Transportation, and the State of Tennessee.


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

to the Federal Highway Administration:

Modify the National Bridge Inspection Standards to require follow-up or diver inspections of those bridges with underwater members that cannot be examined visually, or by feel during scheduled bridge inspections because of excessive water depth or turbidity. (Class II, Priority Action)(H-90-56)

Require States to develop and maintain channel profile records for bridges over water, and to evaluate the channel profile records to determine the effects of channel changes on bridges. (Class II, Priority Action)(H-90-57)

Modify the National Bridge Inspection Standards to require qualifications for personnel who evaluate bridge inspection reports. (Class II, Priority Action)(H-90-58)

Require States to develop a crucial element checklist for each bridge based on the bridge design and as-built plans, or available bridge data. The list should identify bridge elements or conditions that when damaged, exposed, corroded or deformed would independently cause a sudden unexpected collapse of a section of the bridge. This list should then become part of each bridge inspection report. Further, require the States to immediately close the bridge or perform needed repairs when an inspector discovers the deterioration of a bridge element contained in the crucial element checklist. (Class II, Priority Action)(H-90-59)

Require that States review overweight vehicle traffic, to evaluate the effects of frequent overweight loads on unposted bridges. Require that, based on these evaluations, the States limit the number or size of overweight vehicles permitted to cross those bridges that may be damaged because of frequent exposure to heavy loads. (Class II, Priority Action)(H-90-60)

to the American Association of State Highway and Transportation Officials:

Modify Section 1.3.2, "Hydraulic Studies" of the Standard Specifications for Highway Bridges to include evaluations of geomorphic changes in streams caused by the construction of a new bridge, and the effects of those changes on existing structures. (Class II, Priority Action)(H-90-61)

Modify section 2.3, "Frequency and Level of Inspection" of the Manual for Maintenance Inspection of Bridges to include a requirement that bridge inspectors be provided with available bridge design or as built plans during on-site bridge inspections. (Class II, Priority Action)(H-90-62)

Modify section 4.6, 'Rating of Bridges, Limiting Vehicle Weights' of the Manual for Maintenance Inspection of Bridges to delete the section which exempts certain concrete bridges from load posting. (Class II, Priority Action)(H-90-63)

to the Tennessee Department of Transportation:

Modify TDOT bridge rating criteria to remove the requirement that a structure show some settlement or leaning before it is rated critical. (Class II, Priority Action)(H-90-64)

Modify bridge inspection procedures to provide inspectors with available bridge design or as-built plans during on-site bridge inspections. (Class II, Priority Action)(H-90-65)

Expand TDOT bridge inspection criteria to require that submerged bridge elements, that cannot be fully examined by bridge inspectors during scheduled inspections, receive follow-up or diver inspections. (Class II, Priority Action)(H-90-66)

Establish an inter-disciplinary team of geotechnical, hydraulic, and structural engineers to develop the repair and rehabilitation programs for those bridges that are determined to be scour-critical. (Class II, Priority Action)(H-90-67)

Immediately repair those bridges determined to have exposed friction piles. (Class II, Priority Action)(H-90-68)

Train TDOT personnel involved in bridge inspections to evaluate scour, in accordance with the FHWA Technical Advisory “Scour at Bridges” and other FHWA and AASHTO publications concerning the inspection of underwater bridge elements. (Class II, Priority Action)(H-90-69)

Modify bridge inspection report review procedures to require that hydraulic engineers review and evaluate all bridge inspection reports which identify the presence of scour or channel migration; and emphasize the identification and correction of channel movements and scour. (Class II, Priority Action)(H-90-70)

Obtain weight per axle and axle spacing information for overweight vehicles when issuing overweight permits. (Class II, Priority Action)(H-90-71)

Establish a priority ranking system for maintenance recommendations issued as the result of bridge inspections. (Class II, Priority Action)(H-90-72)

to the State of Tennessee:

Provide Maintenance resource necessary to complete recommended repairs developed as a result of bridge inspections. (Class II, Priority Action)(H-90-73)

As a result of its investigation of this accident, the National Transportation Safety Board reiterates Safety Recommendation H-89-72 to the American Association of State Highway and Transportation Officials:

Modify Section 4.5 “Rating of Bridges, Evaluations” of the Manual for Maintenance Inspection of Bridges to require the evaluation of substructural bridge members during load rating calculations. (H-89-72)