A Black Box Under My Car Seat?

Many people are surprised--and some shocked--when told that a Black Box, aka Event Data Recorder, is installed under the seats of their cars to record data. These recording devices have been in some vehicles since the 1970s. The 1974 Cadillac was the first vehicle to have one.

The beginning of the Event Data Recorders (EDR) started with the installation of air bags. EDRs control the deployment of air bags. Sensors and associated microelectronics are mounted on the vehicle to determine when conditions are correct to deploy the air bags. The sensors feed information into the Event Data Recorder and the EDR makes the decision to deploy or not to deploy the air bags.

For example, hitting a deep pothole in the roadway will not cause your air bags to deploy. But in the event a vehicle crashes into your car, the EDR (or Black Box) will tell the air bags to deploy. This is a good thing.

Many lives have been saved in vehicle accidents because the air bags popped out before the occupants hit the windshield. Instead of hitting the windshield, the occupant contacts the air bag which acts as a cushion.

Supplemental Restraint System (SRS)

SRS is seen on the steer columns of many automobiles. It stands for Supplemental Restraint System. The SRS consists of crash sensors, the event data recorder and air bags. In the event of a collision, the crash sensors send a signal to the event data recorder. The event data recorder analyses the change in the velocity and decides whether to activate the air bags or not. This analysis happens in about 1/10 of a second.

The Event Data Recorder is part of the SRS. The EDR performs three major functions:

1. It activates the air bag system when a crash is detected.

2. It monitors the functions of the SRS and alerts the driver to any malfunctions.

3. It stores data reported immediately before and after the time of a crash.

The Black Box

The Event Data Recorder is also known as a “Black Box.” Only it isn’t black, it is silver. The size of it is approximately 4 inches by 4 inches by 2 inches. It is located under the front seat and attached to the frame of the car under the carpet. The carpet has to be removed to get to the black box module.

The National Highway Traffic Safety Administration (NHTSA) defines the EDR as a device installed in vehicles to record technical data and occupant information for the time before, during and after a crash. The original purpose of the EDR was to monitor and assess the performance of the vehicle’s safety system.

Black Box Data

Typical data which can be downloaded from an Event Data Recorder are:

· Vehicle Speed

· Engine speed

· Seatbelt usage

· Braking Status

· Throttle position

· Air bag deployment

Event Data Recorders in cars are not mandatory. Automobile manufacturers choose to include or not to include them in their automobiles. They also choose whether to make their data available for downloading.

The National Highway Traffic Safety Administration (NHTSA) has issued a ruling on EDRs that will apply to the 2013 and later models. The ruling does not require manufacturers to install EDRs in their vehicles. The data will be standardized for manufacturers that choose to install Event Data Recorders. NHTSA has defined fifteen data elements that must be recorded in vehicles with EDRs after 2013.

When is Data Recorded?

I have often been asked; how does the Event Data Recorder know when to record data?

A vehicle has sensors located in several locations on the vehicle. These sensors measure the change in velocity of the vehicle. The change in velocity can be a slowing of the vehicle by normal application of the brakes or the change in velocity can be the slowing of the vehicle involved in a head-on collision.

We certainly don’t want our air bags to deploy when we hit a pothole. The sensors measure the deceleration of the vehicle and tell the air bags to stay cool-not to deploy. This is known as a non-deployment event. The severity of the impact does not reach a preset threshold to deploy the air bag system.

If we are involved in a head-on collision, we want the air bags to deploy. The air bags can make the difference in surviving an accident or not surviving. These same sensors make the decision to release the air bags in about 1/10 of a second from the time of first contact of the two vehicles.

After an air bag deployment, the Event Data Recorder (Black Box) permanently locks data in its memory. The data cannot be overwritten and is available to be downloaded and analyzed.

The Value of Event Data Recorders

The Event Data recorder has two valuable functions. First, design engineers use this information to improve the performance of air bag sensing systems and NHTSA researchers use it to help understand the field performance of air bag designs. Researchers and safety engineers working to develop safer highway transportation systems utilize the information captured by EDRs.

Second, the data can be downloaded by Traffic Accident Reconstruction Engineers to help better understand what happens in automobile accidents. In a crash event, the Event Data Recorder records pre-crash data such as vehicle speeds, engine throttle, application of brakes and seatbelt usage.

A case example of the use of the data from an Event Data Recorder (or Black Box) occurred in an intersection accident. Our client turned left in front of an oncoming vehicle. He was charged with failure to yield.

Our investigation revealed that no tire marks were left on the pavement. The accident happened during a rain and the pavement was wet. The location of the vehicles was documented and the crush damage measured.

Our analysis of the crush damage showed the oncoming vehicle was traveling approximately 45 miles per hour at the time of impact. This was below the posted 50 mph speed limit.

The data was downloaded from the Event Data Recorder. It revealed the oncoming vehicle was indeed traveling about 45 mph at impact. But, it also showed that the oncoming vehicle was traveling at 70 mph three seconds prior to impact. It also showed hard braking prior to the collision. The driver was able to slow to 45 mph by the time the impact occurred.

Had the oncoming driver been traveling at the speed limit, the crash would not have occurred.


The Event Data Recorder (or Black Box) records data before, during and after a collision. It has been in automobiles for years. It provides information about vehicle speeds, brake application, throttle position and seatbelt usage. The data helps Engineers understand how accidents happen and often supply the missing pieces to a reconstruction of an accident.

This article is submitted by Elvin Aycock, PE, ACTAR. Mr. Aycock is a Professional Engineer and a certified Traffic Accident Reconstruction Engineer. He is the owner of Atlanta Engineering Services and has more than 16 years of experience in traffic accident reconstruction and Event Data Recorder downloads. You may email him at ela@atlantaeng.com or visit him at www.atlanta-insurance-claims-resource.com or www.atlantaeng.com for more information.

Additional articles you may find to be of interest:

The Insurance Company's Claims Handling Process

Fraud Indicators in Insurance Claims

What to do When You have Been Involved in an Automobile Accident

What to do if You are Sued as the Result of an Accident

Contributory Negligence Laws

Comparative Negligence Laws

The Last Clear Chance Rule regarding Negligence or Liability

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