Twice in four days, semis carrying heavy equipment struck the overpass bridge at the Eklutna exit while traveling out of Anchorage on the Glenn Highway. Monday’s bridge strike appears to have taken a chunk of concrete about the size of a car door from one beam that spans the highway. Commuters gawked, Flashlight stopped for photos, and within about five hours the Anchorage Daily News posted a story, sans bridge expertise, that featured Anchorage Police Department spokesman Dave Parker commenting about how the too-tall arm of a backhoe struck the bridge. Parker said the crash happened during rush hour and the truck driver was adept enough to make it under the bridge without involving other vehicles, except those that followed behind and were hit by debris. No one was injured, Parker reported, and the trucker pulled over to wait for police.

Turns out the ADN website’s commenters wanted more info, and a few of them had a bit of knowledge about trucks and bridges. The Eklutna overpass has been struck pretty often—so often state of Alaska DOT engineers installed a fancy-schmancy device they call the “over-height vehicle detection system” on either side of the bridge.

Flashlight is no bridge expert, so we called on Rick Feller, the Central Region spokesman for DOT. Feller admits he is no bridge expert either, but by Wednesday, he seemed to have been fully briefed. The over-height system is high-tech, but “not a fail-safe,” he says. “That was a system that was installed with grant monies, and it’s kind of an advanced high-tech system. Once installed, we ran into difficulties fine-tuning the system. It had been giving false readings,” Feller says, adding that at times the system has been turned off to avoid the false warnings. Another DOT source tells us it uses z-patterned infrared beams to measure moving vehicles.

The sensor-and-warning combo as installed as part of a project called the Glenn Highway ITS, for “intelligent transportation system.” (Yes, we know: irony. But please remember that irony is dependant on point-of-view. The people close to this situation know the bridge gets smacked pretty often. Irony also requires the unexpected to happen. People with a bit of knowledge about the overpass likely expect such collisions to continue even as they work to improve their solutions.)

The sensors at Eklutna trigger a siren and flashing lights. That system is meant to get the offending truck either onto the off-ramp or stopped before a collision with the bridge. “I believe that when this incident happened, the southbound detection system was working, but the northbound system was turned off,” Feller says.

Feller says bridge inspectors were expected to finish a report Wednesday that will tell DOT what to do next. As of Wednesday morning, DOT had cones placed on the bridge deck to limit traffic over the damaged beam. The cones are meant to prevent more concrete from rattling loose and falling into traffic.

The bridge was first constructed in 1978, according to a DOT inventory of bridges published online. A bridge-height map available at the Alaska Trucking Association website (aktrucks.org) says the bridge height is 15 feet and ten inches over the southbound lanes. Over the northbound lanes, the bottom side of the bridge is 16 feet, one inch over the highway.

“All of the [bridge] clearances out there are public knowledge and we promote those, and the ATA promotes those,” Feller says. He says if a shipper knows their load will be too tall, they must apply for a permits before hauling the load. Knowledge about bridge heights (measured periodically and updated by inspectors) is reinforced during the permitting process for each haul.

“They would have been told,” Feller says, “…and [that communication] is really the best mechanical solution we have.”

Feller didn’t know how many times the overpass has been struck since it was built, or since the sensors were installed. (Flashlight didn’t have time to request the info and get it before deadline—our apologies to the data junkies.)

“You can say without question that this bridge has been struck before,” Feller says. “It has required anything from a simple concrete patch job to the replacement of an entire girder.”

scott@anchoragepress.com