Interestingly, NHTSA’s proposal noted that "As of now, GM, Ford and Toyota record what would be considered a large amount of crash data. Honda, BMW and some other vehicle manufacturers record small amounts of crash data. Given these trends, we do not believe it is necessary for us to propose to require EDRs at this time."

Millions of vehicles on the road today are already equipped with some form of EDR. NHTSA estimates that 65 to 90 percent of model year 2004 passenger cars and other light vehicles have some recording capability. In 2000, Vetronix Corporation released its Crash Data Retrieval (CDR) system, a tool that allows investigators to access and download data stored in certain vehicle EDRs. It is estimated that about 40 million vehicles on the road have EDRs that can be read using the CDR tool, including nearly all new GM vehicles and some Ford vehicles.

Nearly every new General Motors vehicle is equipped with an EDR or "black box", more correctly known as the air bag Sensing and Diagnostic Module (SDM). The air bag module is the vehicle’s "computer" that controls air bag deployment. The SDM consists of an accelerometer, low pass filter, and microcomputer, which includes a data recording feature. While these devices are not nearly as sophisticated as the flight data recorders used on airplanes, they capture and store data that can be particularly useful in analyzing and reconstructing accidents.

Recordable air bag modules have been installed in selected GM vehicles since 1990. In 1994, GM introduced an enhanced module consisting of a single solid state analog accelerometer and a computer algorithm integrated into an SDM. The SDM computed and stored the longitudinal vehicle velocity change (delta-V) during the impact to provide an estimate of crash severity. It also added the capability to record the status of the driver’s seat belt switch (buckled or unbuckled).

The newer versions of the SDM, in use on certain 1999 and nearly all 2000 and later model year GM vehicles (including passenger cars, SUV’s and light trucks) capture and store approximately five seconds of pre-crash data including vehicle speed, engine RPM, throttle position and brake switch on/off status. In addition, detailed delta-V versus time data, seat belt status, ignition cycles, and air bag system status are recorded for the crash. Depending upon the particular vehicle, additional data may be captured.

There are two different types of SDM recorded crash events. The first is called the non-deployment event. A  non-deployment event is an event severe enough to wake up the air bag sensing algorithm, but not severe enough to deploy the air bags. A non-deployment event will generally be over-written by any subsequent event having a greater velocity change, or it will be cleared from memory after the ignition has been cycled 250 times.

The second type of recorded crash event is the deployment event. A deployment event is an event severe enough to deploy the air bags. This causes the SDM to permanently store the data. Deployment events cannot be overwritten or cleared from the SDM and, therefore, can be retrieved at any time after an accident.