|View of fallen girder looking to the west.|
In response to the accident and its probe, the NTSB on May 31 voted unanimously to recommend new construction standards and better supervision by state highway departments, as well as consistent federal and state guidelines for design and certifying falsework for bridges and other highway structures.
The federal board investigates transportation accidents and recommends actions to improve safety, but has no regulatory authority. Although NTSB has investigated bridge collapses over the years, officials said the probe of the Colorado accident appears to be its first of an active highway construction site.
In its May 31 meeting, the board also approved a multi-factor probable cause for the accident, which took place on Interstate 70 in Golden, Colo. The accident occurred on May 15, 2004, when a temporarily braced, 200-foot-long steel girder, installed as part of a project to widen an overpass, rotated and fell onto I-70 beneath it. The girder struck a sport utility vehicle traveling under the overpass, killing the driver, William J. Post, his wife Anita and their two-year-old daughter, Koby Anne.
In a summary of its findings, NTSB said the accident's probable cause "was the failure of the girder's temporary bracing system due to insufficient planning by [subcontractor] Ridge Erection Co., [prime contractor] Asphalt Specialties Inc. and the Colorado Dept. of Transportation., which were responsible for putting the girder and its bracing in place, and due to deficiencies in the installation of the girder and the bracing, so that the bracing failed to adequately secure the out-of-plumb girder to the existing bridge deck."
NTSB said contributing factors included a "lack of uniform, consistent bracing standards" and Colorado DOT's "narrow definition of falsework" and the department's "failure...to effectively oversee safety-critical contract work for the project."
NTSB project manager Michele McMurtry told the board that the plan was to install a pair of parallel, 200-ft-long girders, each made up of two sections, during a work period the night of May 11 and early morning hours of May 12. But the construction team "began to encounter problems," she said. That included not having appropriate tools at hand, confusion about markings on a girder section that initially led workers to position the section backward. Moreover, McMurtry said, the holes drilled were too shallow, so the bolts to be used were too long.
Those problems slowed down the work and with the hour nearing at which the highway was to reopen for the day, the team decided to install just one girder and brace it temporarily to the deck of the existing overpass. Poor weather prevented finishing the job the next night.
Dan Walsh, NTSB highway engineer, added that there were problems with the temporary bracing. He said it wasn't flush with the bridge deck and some bolts were not embedded in concrete, contrary to manufacturers' requirements, and the diameters of holes in the deck were larger than those of the bolts to be inserted in them.
Bruce Magladry, acting director of NTSB's office of highway safety, said, that if the falsework had "been plumb, this type of bracing system would have worked." Walsh said that contractor and CDOT officials should have seen that the system was out of plumb.
Magladry also said that the oversight of the construction process "is the big issue for us."
On May 15, the new girder rotated toward the overpass deck and slumped onto the highway below, where it struck the Posts' vehicle.
NTSB Acting Chairman Mark Rosenker called the sequence of the steps on the job "just flat-out sloppy." Board member Kitty Higgins added, "This is an accident that should never have happened."
Colorado DOT Executive Director Tom Norton said in a statement that his agency "will do whatever is necessary to prevent a tragedy like this from ever occurring again." He said that in August 2004, after an internal review of its safety and construction management procedures, the department changed its specifications to improve safety of installing girders.
The changes include: requiring contractors to submit an plan with "complete details" of the erection process for a project; and having a licensed professional engineer to approve and seal that erection plan. In addition, the contractor's engineer must inspect and approve each installation phase before a structure can be open to traffic and the contractor and CDOT personnel must do daily inspections of the girders until the bridge deck concrete work is finished.
Norton added that "we are deeply saddened that something so terrible could occur on one of our projects. We understand that there is a belief that our inspectors or project managers should have been able to tell that the girder was potentially unstable. While CDOT staff did meet the contractual requirements that were in place at the time of the tragedy, I know that everyone involved wishes they had discovered the potential hazard at the site prior to this event."
An official at Asphalt Specialties, who declined to be identified, said he hadn't seen the NTSB's findings and recommendations and had no comment.
In a November 2004 settlement, the state of Colorado and its DOT, Asphalt Specialties, Ridge Erection and insurers agreed to pay $1.5 million to the parents of William and Anita Post and the Posts' estates. The state DOT said at the time that, "The settlement is not an admission of liability."
As is the board's practice, its full report on the accident won't be available for four to six weeks. The summary, including recommendations and the probable-cause findings, is available on www.ntsb.gov, under "accident reports."
(Photo courtesy of NTSB)he National Transportation Safety Board has determined that poor construction and planning and inadequate state oversight were among factors that contributed to a 2004 accident in Colorado, in which a falling bridge girder killed a family of three.