Electronic Data Recorders
Most motorists don't realize that they have something of a "spy" in the engine compartment. If you drive a General Motors vehicle, or a more recent make of Ford, it is highly likely that a mechanism connected with your air bag creates a snapshot of your vehicle's operation in the seconds before any event that triggers the airbag. If you are operating a heavy-duty vehicle of fairly recent vintage, it is highly likely that it contains a computer that is designed and programmed to preserve similar data. In the case of snowplows, fire engines and semi-tractor trailer units, for example, even a hard-braking stop will "capture" the speed of the vehicle immediately prior to the capturing event.
In some cases, this data is captured "permanently". In other cases, it may be over-written after a certain number of braking events or after a certain number of engine starts. We have found that while these computer systems are not foolproof, they tend to be more reliable than an at-fault driver when it comes to estimating speeds, for example. It is imperative that anyone investigating a motor vehicle incident thoroughly investigates the potential content of an electronic data recorder or "black box".
Most foreign-manufactured passenger vehicles do not contain an EDR. In the case of some heavy-duty vehicles, the owner can determine what information will be preserved by stipulating that the computer not be activated or partially disabled.
EDRs were originally installed by General Motors in an effort to defend consumer claims of manufacturing or design defect. They can also be useful in some commercial applications to assess whether the vehicle's operation is consistent with regulations governing hours of service, speed and hours of rest. We have found that even investigating police agencies may overlook the potential for EDR evidence, if the officer is not highly familiar with the concept and willing to explore what is available. For example, in one of our recent cases, the Sheriff's Deputy did not preserve evidence temporarily captured by a snowplow that struck a pedestrian because he did not understand that the simple act of braking hard would activate the systemâs memory.