July 12, 2005
February 14, 2003
Videos were presented at the Board meeting July 12, 2005 in Washington, D.C., for the Hewitt, TX Highway Accident Investigation.
Disclaimer: Simulations presented below used scene surveys and pavement friction testing, witness statements, vehicle and tire testing, vehicle plans, vehicle operating characteristics and a crash data recorder. The depictions are shown with clear visibility.
Vehicle Dynamics: Five different views of the vehicle dynamics were rendered to show various perspectives of the crash. In the simulation, the initial speed of the bus was 63 mph, and the bus increased to 65 mph at the bottom of the hill prior to decelerating on the uphill to 61 mph before braking followed by steering was initiated. The bus slowed to about 40 mph as it collided with a Chevrolet Suburban traveling at 33 mph in the opposite direction. The bus rolled onto its side and slid to final rest, while the Suburban spun, climbed an embankment and then slid along the top of the bus's roof to final rest. Additionally, two videos of tire testing at the Calspan facilities in Buffalo, New York showing braking, and a cornering test are available.
HewittBusChaseClear.wmv (Video = 1.7MB)
This is an aerial chase view of the bus in real time in clear conditions.
HewittBusDriverViewClear.wmv (Video = 1.7MB)
This is the bus driver's potential view in clear conditions. Bus steering and braking inputs are indicated at the bottom of the view. This is in real time.
HewittFixedClearCollision.wmv (Video = 1.1MB)
This is a fixed view of the collision in clear conditions. This is in real time.
HewittSuburbanDriverViewClear.wmv (Video = 1.2MB)
This is the Suburban driver's potential view in clear conditions. The Suburban's braking inputs are indicated at the bottom of the view. This is in real time.
HewittGoodTiresChaseClear.wmv (Video = 1.3MB)
This is a simulation of a chase view of the bus. In this simulation the bus has tires that are in good condition and the same braking and steering are used as in the accident simulation. The simulation was stopped after the bus stopped traveling into the opposing lane.
The vehicle dynamics simulations were produced on an HVE™ PC system using SIMON™, EDSMAC4™, EDVSM™ and EDGEN™ programs. All of the programs are trademarks of the Engineering Dynamics Corporation. The software, ReadDataFile, developed by Collision Engineering Associates, was also implemented for the simulations. These movies were produced in Adobe Premiere™. This program is a trademark of Adobe Systems Incorporated.
Testing was conducted for NTSB by Calspan on four of the bus tires, representing the best and the worst tires, at 40, 60 and 70 mph, with 0.02, 0.11 and 0.19-inches of water for longitudinal braking and cornering. The results from this testing were used to model the bus tires in the simulation. The tire test results are available from the docket. The videos below show a tire braking and a cornering test.
Tire_brake_test_25.wmv (Video = 0.7MB)
Tire_cornering_60_mph_test_6.wmv (Video = 0.6MB)