After a truck has been involved in a wreck, driving it even a couple feet at the crash scene without first disconnecting the vehicle speed sensor (VSS) will almost certainly destroy any last stop data recorded by the Heavy Vehicle Event Data Recorder (HVEDR), whether it is an Engine Control Module (ECM), an Electronic Control Unit (ECU), or some combination. This loss of digital evidence has often been cited as evidence spoliation, which can have serious repercussions.
This situation is easy to avoid by locating the speed sensor near the transmission output shaft, and disconnecting the electrical plug from the speed sensor. Let the plug hang free. The truck many then be driven or towed without danger of overwriting and losing important data.
It is important to make this common knowledge for truck drivers, wrecker drivers, investigating police officers, and truck service and maintenance personnel. This information can be disseminated through training classes and service bulletins. Labels on trucks near the VIN, near the toll-free number decal for the trucking or adjusting company, and on the accident packet can also help at the crash scene. Here’s a suggested label:
After a crash, do not drive or move vehicle at all without disconnecting vehicle speed sensor.
Various CVSA (Commercial Vehicle Safety Alliance) Out of Service (OOS) violations may be found when inspecting heavy trucks. These can be maintenance or safety items that fail to meet the criteria in Appendix G of Subchapter B of the FMCSR (Federal Motor Carrier Safety Regulations) (40 CFR §396.17). This post will focus on brake issues only.
CVSA uses the term “defective” to denote a brake condition that does not meet specific criteria. CVSA declares a vehicle OOS if twenty percent of the brakes are defective. A common three axle tractor with a two axle semi-trailer will have ten brakes total. Twenty percent of ten brakes means the truck would be put OOS if two brake defects were found. (Click on image to enlarge, then click on back arrow to return.)
CVSA brake defects often result from inadequate maintenance. One important purpose of a CVSA inspection is to catch maintenance issues before they adversely affect the stopping ability of the truck. While it is essential to properly maintain vehicles for safe operation, the presence of one or more OOS brake defects does not necessarily mean the braking ability of the truck was compromised at the time of the accident. So there are two separate, but related issues: -1- Were there any problems with the truck? -2- Did any of those problems affect the truck’s ability to stop during this particular incident? Continue reading “Out of Service (OOS) Brake Defects and Brake Force Calculations”