Bay Area Overpass Collapse Documented with
3D Laser Scanning
By Bruce Jenkins, Senior Analyst, Spar Point Research LLC
Early on Sunday, April 29, a gasoline tanker truck crashed and burned on a connector ramp near Oakland, CA, in a complex freeway interchange called the MacArthur Maze. The driver walked away with only second-degree burns, and due to the early hour there were no fatalities. But the resulting fire melted bolts and deformed girders on an overpass above the crash site, pulling it off its supports onto the roadway below.
At 7:30 a.m. Lieutenant Dave Fox, Team Manager for the California Highway Patrol's Multidisciplinary Accident Investigation Teams (MAIT), called Tony Grissim, Forensic Account Manager for Leica Geosystems, to tell him that a MAIT team from CHP's Valley Division was heading to the scene to document it using 3D laser scanning. Grissim offered the CHP Leica's assistance, then started making calls to Caltrans and to Leica employees living near the accident scene. An opportunity was unfolding in which laser scan data captured in a police investigation could also aid engineers assessing damage to the structure and planning the engineering effort to reopen the roadway.
The CHP currently owns five Leica Geosystems ScanStation systems which it acquired late last year, and five MAIT teams are trained in their use. The scene at The Maze would be CHP's largest and most complex laser scanning project to date.
California Highway Patrol Multidisciplinary Accident Investigation Team (MAIT) members document MacArthur Maze accident scene with 3D laser scanning. The roadway that collapsed carries eastbound traffic from the Bay Bridge onto I-580, I-980 and state Highway 2. The roadway below, also severely damaged, connects southbound I-80 to I-880. Photo courtesy California Highway Patrol and Leica Geosystems
Scanning team stays just ahead of demo crew
Because of risk of further collapse as the structure cooled, scanning did not start immediately. But no further collapse occurred, and once it was determined that the structure was relatively stable, MAIT members began scanning in mid-afternoon. In the middle of the third scan Leica's Frank Collazo arrived on scene and offered his assistance to the CHP. This MAIT team had received Leica's police-specific scan training in January, and needed minimal help. "The MAIT officers were pretty self-sufficient," said Grissim. "We just offered a few pointers here and there, and suggested setting a few additional survey control points so Caltrans could follow behind with a conventional survey crew and reference the entire point cloud to state plane coordinates."
Meanwhile Caltrans expedited hiring of a contractor to demolish the collapsed structure. The contractor reached the site during the evening and started demolition - the CHP scanning team was literally staying just ahead of the demo crew, Grissim says.
Scanning eventually concluded after midnight. During this time California Governor Arnold Schwarzenegger and local mayors arrived and toured the damage, and the subsequent news conference with the scene still smoldering in the background was broadcast live.