UPDATED -- Getting to the root cause of the Skagit River Bridge collapse will be easier than assigning blame, I think. The physics of the bridge strike are already fairly apparent. A truck hauling an oversize load struck one of the overhead supports on the Interstate 5 bridge near Mt. Vernon, Wash., last Thursday, and the bridge collapsed.
Who can help but question why a couple of displaced structural components would allow the whole thing to come crashing down? Even in 1955, when the bridge was built, I have to assume that engineers would have designed some redundancy into the supporting structure.
I have read no reports so far that suggest the bridge was in poor physical condition. It's old, and structurally outdated, but that doesn't mean it is structurally deficient. Perhaps that level of redundancy wasn't required in 1955. If that's the case, and it was built to the corresponding engineering codes of the day, I guess we just have to expect these things to happen.
It's like the old Knob & Tube electrical wiring once used in almost every home in North America. It worked fine in its day, but we don't use it anymore because we have since developed safer wiring systems.
If Washington state DOT officials were aware of the structural shortcomings of such bridge structures, you'd think the very least they might have done would to put up warning signs urging higher profile loads to move into the left lane and away from the sensitive components.
There was no such warning sign on the Skagit River Bridge.
We've been told that WSDOT issued a permit to Mullen Trucking to move the load, and the permit was apparently in order at the time of the strike. The permit allowed the movement of a load up to 15 feet 9 inches high. The center of the arched girders spanning the width of the bridge is about 17 feet above the roadway, so no problem there. The outer extremities of those arched girders, however, are just 14 feet 5 inches high.
I'm not really good at math, but even I can see that a 16-foot load won't go through a 14-and-a-half-foot hole without a fight.
It strikes me that the bridge has been around long enough for someone at WSDOT to have red-flagged that bridge -- and others like it, with variable clearances -- so that when permits are issued, the shape of the opening is brought to someone's attention.
For heaven's sake, somewhere in the course of time, somebody thought to put labels on chainsaws warning against using your hands to stop the chain, against using your lawn mower as a hedge trimmer and against using a hair dryer in the shower. That such an obvious "problem" with a bridge could have escaped an agency the size of WSDOT is awe-inspiring.
And then the state has the gall to put on the permit that the State "Does Not Guarantee Height Clearance." Why go through the harangue of obtaining a permit if the state won't stand behind the clearances it authorizes or take any steps to ensure they are accurate.
What about the pilot car?
Here's where the fur will really fly when this makes its way into court, as I'm sure it will.
Washington State has specific rules regarding the use of pilot cars and escorts for oversize loads. It's also one of a few states that have regulations in place regarding the qualifications and credentialing of pilot car operators. The Evergreen Safety Council, a private non-profit organization, developed the certification program based on regulations established by WSDOT. Several other states and some Canadian provinces have adopted those certifications as well.
There are also very specific rules about when pilot cars must be used, and more importantly in this case, when height poles must be used.
To sum up, the rules say a pole must be in use at all times when load is over 14 feet, 6 inches high. Further, the rules say the pole must extended at least 3 inches higher than the load, but not more than 6 inches above the load's maximum height.
A photo in the Seattle Times clearly shows the pilot car to have a pole installed. While I'm not privy to the information, I'd guess officials have already measured the pole to ensure compliance, and since we have heard nothing to the contrary, I'm going to assume the pole met the requirements.
The pole, like a cat's whiskers, is designed to keep trucks out of trouble. If the pole won't fit, neither will the load. Brakes on, day saved. Not this time.
The pilot car driver has to alert the truck driver that the pole has struck an overhead object – and the driver has to heed the pilot car's warning. I'm thinking in this case, that bit of dialog didn't go according to plan.
Published reports quote Deborah Hersman, chairman of the National Transportation Safety Board, as saying the driver of the pilot car did not radio the trucker to warn about the span.
Further, reports say, the truck driver says he and the pilot car were both travelling in the right lane, closer to the shorter side of the bridge, as they crossed the span. At the same time, Hersman has said, another commercial vehicle was traveling in the left lane, where the clearance is higher.
Heather Murray runs Sparrow Pilot Services of Saskatoon, Saskatchewan, and she is a seemingly tireless advocate of a more structured environment for pilot car operators and truckers who more oversize loads. She says the pilot company is supposed to make sure the load can travel on the prescribed route, and the pilot car is responsible for clearing the way for the truck.
"The pilot should have known the route and the hazards along the way," she told me. "The pilot car should have moved the truck over to the left well before the bridge."
Murray is active within the pilot service community, and she has already heard from several of what she calls trusted sources that the pilot car's pole did in fact strike the bridge. News like that would have traveled quickly through a community whose job it is to prevent that from happening. At any rate, that kind of thing would leave a mark, either on the pole or on the bridge. That would be some of the evidence NTSB would have gathered by now.
If that's the case, it begs the question, why did the car not alert the driver – or if it did, why did the trucker not heed the warning?
Murray says she can't imagine why the truck didn't stop.
"There might have been some extra chatter on the radio," she says. "Or maybe both were keying the mic at the same time.
"Normally the pilot car travels about half a mile ahead of the truck – further if the pilot wants to check something out or has reason to suspect a problem ahead – which would have given the trucker about 30 seconds of warning before hitting the bridge," she says.
Given what Hersman said about another truck in the left lane, making it impossible for the Mullen driver to move over, the obvious next option would have been to stop. From 60 mph with adequate warning, that seems quite doable.
The other possibility is that the pilot car driver wasn't aware that the pole had hit the bridge. From the photo in the Seattle Times, you can plainly see the pole mounted on the right-hand side of the pilot car, where it would have provided the best warning against an arched girder such as the ones on the Skagit Bridge.
However, Murray says the top of the pole would have been impossible to see from the driver's seat in the pilot car. Think in terms of an overhead traffic signal when you get too close to it. You need to crane your neck looking straight up to see it. She says some cars, like hers, have a mirror on the fender to help see the top of the pole.
But Murray says it's almost inconceivable, yet possible, that the driver would not have heard the pole hit.
"Some poles have sensors at the tip to alert of a strike," she says. "It would have made quite a sound at highway speed, but there's no guarantee the driver would have heard it."
Their Day in Court
Given what's at stake, it's a safe bet this one will wind up in court, and it may come down to one driver's word against the other. But I just can't see the State of Washington getting off scot-free on this one.
"If the dimensions were given to the state and the state gave the go-ahead on the permit, that raises some questions about responsibility," says retired over-size and heavy-haul veteran Al Koenig, formerly with Midwest Transportation Services. "With the number of overhead bridges in this country, it would be a real task to keep track of all the changes to bridge construction, but if the state itself can't keep track of it, who else can?"
Considering the minimal damage to the unit being hauled on the trailer, which is totally inconsistent when the calamity it caused, there must have been some inherent vulnerability in the design or in the structure of that particular bridge. If it was that vulnerable, you'd think the state would post warnings urging tall loads to use the left lane. Yet there are no clearance signs posted on the bridge at all. That doesn't seem reasonable to me.
Should the pilot car company have known about the shape of the arched girders on the bridge? You'd think so. It's supposed to be a local company, and if that's their territory, it would seem reasonable it would be aware of such threats.
Should the trucking company and the driver have been aware of the diminishing clearance on the bridge? I think it would be prudent to research the route looking for threats or inconsistencies in the permit.
When it comes to such shared responsibilities, Koenig says carriers rely heavily on their escorts to know the territory.
"Pilot car companies are responsible for catching the changes or inconsistencies in the routing and permit," he notes. "The pilot car is responsible for clearing the way for the truck. They should have known the route."
Consequences aside, there's no event in the history of modern transportation that can be put down to a single contributing factor. I think in this case, we'll find a handful of factors led to the disaster including possibly human error, misplaced assumptions, lack of official oversight of the bridge, bad timing (the passing truck), and probably more.
The important thing is that we have to learn from this and start marking overhead structures with actual clearances above the road deck.
-- Update includes a revised reference to the role of the Evergreen Safety Council