The National Transportation Safety Board today determined that the probable cause of the Robert Y. Love allision with the Interstate 40 bridge in Okalahoma and its subsequent collapse was the captain's loss of consciousness, possibly as the result of an unforeseeable abnormal heart rhythm. Contributing to the loss of life was the inability of motorists to detect the collapsed bridge in time to stop their vehicles.
On May 26, 2002, the towboat Robert Y. Love, pushing two empty tank barges, was traveling northbound on the McClellan-Karr Arkansas River Navigation System, near Webbers Falls, Oklahoma. As the tow approached the Interstate 40 highway bridge, it veered off course and rammed a pier west of the navigation channel. The impact collapsed a 503-foot section of the bridge, which fell into the river and onto the barges below. Highway traffic continued to drive into the void created by the collapsed spans. By the time traffic stopped, eight passenger vehicles and three truck tractor-semitrailer combinations had fallen into the river or onto the collapsed portions of the bridge. The accident resulted in 14 fatalities and 5 injuries.
"An effective motorist warning system can be a vital tool to prevent tragedies like this from occurring," said NTSB Chairman Ellen Engleman Conners. "With this system in place, the loss of so many lives could have been prevented."
Safety Board investigators found that the captain of the towboat was not impaired due to alcohol or illegal drugs. Further, the captain's incapacitation was probably not a result of his falling asleep. However, he experienced a sudden loss of consciousness, possibly as a result of an abnormal heart rhythm. Such an incident is entirely consistent with an episode of syncope, in which blood flow to the brain is interrupted for any of a variety of reasons. This interruption results in loss of consciousness and falling. The captain had no apparent symptoms of clinical significance prior to the accident and a reasonable clinical evaluation of the captain before the accident was unlikely to have detected the medical conditions that were discovered through postaccident testing.
The investigation also revealed that vehicles either fell with the collapsed sections of the bridge or drove off the bridge into the void. The surviving drivers indicated that they could not see the void in the bridge in time to avoid driving into it. Therefore, the Board concluded that drivers in this accident did not have adequate time to detect, identify, and respond to the hazard posed by the collapsed sections of the bridge.
Board investigators determined that a solution to this would be an effective motorist warning system on or near the bridge and capable of alerting motorists to the bridge failure or directing vehicles to stop. This might have prevented some of the vehicles from driving off the I-40 bridge and mitigated the loss of life in this accident.
As a result of this accident, the Safety Board recommended that the U.S. Coast Guard Research and Development Center evaluate the utility and effectiveness of wheelhouse alerter systems on inland towing vessels. The Board urged the Federal Highway Administration to revise the sufficiency rating system, which prioritizes bridges for rehabilitation and replacement, to include the probability of extreme events, such as vessel impact; and develop an effective motorist warning system to stop motor vehicle traffic in the event of a partial or total bridge collapse. To the American Association of State Highway and Transportation Officials, the Board recommended that once the warning system is developed, provide guidance to the States on its use.
A synopsis of the accident investigation report, including the findings, probable cause, and safety recommendations, can be found on the Publications page of the Board's web site, www.ntsb.gov. The complete report will be available in several weeks.