Most traffic crashes are pretty simple – Car A stops, Car B doesn't, hits Car A in the rear.
When they're not simple, or a crash involves death, serious injury or major property damage (among other factors), the Pennsylvania State Police turn to a small cadre of trained Collision Analysis and Reconstruction Specialists.
That was the case this past weekend, when a bus carrying Seton Hill University women's lacrosse team crashed along the Pennsylvania Turnpike in Cumberland County. The bus's driver and the team's coach, along with her unborn child, were killed.
The cause of the crash remains unknown. The bus traveled through a guard rail and approximately 70 yards across a field before slamming into a grove of trees. The collision shredded the metal side of the bus, leaving a gaping hole.
State police are conducting the investigation, the results of which could take several weeks.
That's not unusual in an in-depth accident investigation. It typically can take weeks or months, depending on how complex a crash is and how many cases a specialist is investigating at a time.
There are roughly 34 trained specialists with the 4,000-odd members of the state police, split between all corners of the state. Their job is a mix of science and police work, a painstaking, detailed analysis to figure out what happened.
“The whole goal is to analyze the crash and determine why the collision occurred,” said Cpl. Tracy Flynn, who heads the specialist unit for the state police.
Speaking generally, an investigation starts at the scene, where troopers collect and record whatever physical evidence might be available -- for example, skid marks.
They review witness statements and also examine the involved vehicles, doing detailed inspections that look at tires, brakes and engines. If possible, data is recovered from airbag computers, or other modules within the vehicles.
Wrecks are weighed, crash zones measured and any other pertinent information is collected and noted.
Then, the analysts use complex physics equations to determine what happened during a crash. And they do it old school, eschewing computer programs and performing the calculations by hand.
Flynn said that while computer simulations are useful, they're still not as accurate as hand calculations. Although, he noted, most troopers then run the numbers through a computerized physics program to double check their work.
“There's a lot of math,” he said. “Technology is great, but doing it by hand is more accurate.”
The calculations (or “energy analysis") is put together with the rest of the physical evidence to figure out what actually happened on the given spot of roadway.
Each report also is reviewed at least four times – by peers and unit commanders – before it is officially “released.”
The need for accurate, dependable results cannot be understated, Flynn said, as often reports are used to build criminal cases and can be key evidence for prosecutors.
“The physics behind it and the evidence dictates (our results),” he said. “There's a lot that goes into it.”
Becoming a specialist is no easy feat either – troopers must apply for positions and then secure four levels of certification, before ultimately passing a test akin to the bar examination.
Even once they pass that hurdle, specialists are required to conduct annual continuing education, often classes in a specialized field such as motorcycles, pedestrian crashes, applied physics and occupant kinematics.
“It's a highly specialized field,” Flynn said. “There's a lot of knowledge that goes into (an investigation).