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ASTM Publishes First Book on Use of Black Box Data for Automobiles

Investigation and Interpretation of Black Box Data in Automobiles by William Rosenbluth is the first technical monograph that describes methods of interpreting electronically-stored “black box” data found in motor vehicle engine, braking, and restraints systems involved in crashes on land. Published in June by ASTM, the 162-page book has been approved by ASTM Committee E30 on Forensic Sciences as well as the Society of Automotive Engineers.

Investigation provides guidance on the location, interpretation, and combination of data parameters that can reveal more than traditional mechanical and reconstruction analysis, according to Rosenbluth, a principal engineer with Automotive Systems Analysis, Inc., Reston, Va. “In many instances,” he said, “this data can provide vehicle operational status at and before the time of a land vehicle accident. The book presents both overviews for attorneys and supervising officials, and detailed technical and mathematical methods for engineers and reconstructionists, and so will benefit both types of readers.”

A systems and electrical engineer, Rosenbluth based the treatise on over 750 system investigations in more than 15 years of vehicle-accident study. “The major benefit of the book will be to teach people already familiar with traditional reconstruction and forensic procedures, additional methods of vehicle post-crash investigation and analysis,” said Rosenbluth. “My book isn’t a handbook, it’s a guide to a methodology. Its end result is that people will learn how to go about interpreting new and better and different data. For the most part, the data is in an encoded form, and to use it you have to decode and interpret data. The encoding language is hexadecimal arithmetic, and the interpretation involves an understanding of the scaling, limits offset and transfer functions inherent in the encoded data record.”

In the preface, Rosenbluth explained how nonvolatile electronically-stored data evolved from mechanical diagnostics to accident applications. “Technology advances within the past 10 years have allowed increasingly sophisticated nonvolatile electronic data storage capabilities on automobiles and trucks,” he begins. “Among the first were electronic odometers, which saved the vehicle cumulative mileage, even if the battery was disconnected. Application of nonvolatile electronic data storage was then incorporated to assist with the diagnosis and repair of intermittent electronic faults that would otherwise be difficult or impossible to diagnose. Systems having the capability to incorporate nonvolatile electronic data storage include engine fuel management (EFI), antilock braking (ABS), automatic traction control (ATC), cruise control (CC), air bags (SRS), and seat belt tensioners (ETR).

“One byproduct of the incorporation of nonvolatile electronic data storage for diagnosis and repair,” he continued in the preface, “is the utility of this electronically saved data to assist land vehicle investigators in determining vehicle conditions before and during an accident in a way unavailable by previous postaccident mechanical analysis techniques. However, because the original intent of this electronically saved data capability was to assist repair, and not necessarily to assist accident investigation, these data are often distributed among several different units, which save data in their own formats and for their own diagnostic purposes (EFI, ABS, ATC, CC, SRS, ETR, etc.).

“In each system that incorporates computer control, the assembly containing the integrated circuit microprocessor unit (MPU) is called the electronic control unit (ECU). Within the ECU, the desired nonvolatile information is saved in EEPROM [electrically erasable programmable read only memory]. This information usually includes diagnostic trouble codes (DTCs), and optional parametric data. Because EEPROM is nonvolatile, it retains its data even when the battery is disconnected. EEPROM data are downloaded from a vehicle ECU using a scanner or via a microprocessor interface, in much the same way as a credit card terminal is used to query a central data bank to authorize a credit purchase. There are two levels of stored data: repair-level DTCs and engineering-level parametric crash data. Generally, repair-level scanners cannot access engineering-level data, whereas engineering-level scanners can access all data.

“As we have discussed above,” he noted in the preface, “certain crash-related data may be stored in the EEPROMs of several vehicle ECUs, requiring the use of several scanners, one dedicated to each type of system ECU, to acquire a complete set of crash data. Newer vehicle models utilize advanced scanners that incorporate multi-system interrogation functions in a single unit.

“Thus, the concept of vehicle black box data is actually an umbrella term, which implies using data components that are obtained by interrogating several different system units that can be assembled to provide a set of electronically saved data useful to the accident investigator.”

Tutorials and conversion tables are covered in chapters on:

• Background and evolution of on-board vehicle data, diagnostics and communications capabilities;
• Geometric conventions, physical laws of motion, acceleration models, and numbering systems;
• A review of air-bag system architecture, components, and stored data;
• A review of antilock-braking bag-system architecture, components, and stored data;
• Finding data in post-crash vehicles and deriving useful data parameters;
• Using ECU electronic data to derive case-specific analyses;
• The future of vehicle black-box data storage;
• Glossary of terms and conversion factors used in vehicle data systems;
• Detailed velocity conversion tables, mph/kph base;
• Scan tools, scanners, bus interfaces, and manufacturer contact;
• Government standards and regulations (CARB, DOT/NHTSA, EPA);
• Industry standards and specifications (SAE, ASTM, ISO, etc.); and
• A comparison of recorded data parameters, aircraft vs. automotive black boxes.

For further technical information, contact William Rosenbluth, Automotive Systems Analysis, Inc., Reston, Va. (phone: 703/860-1766). ASTM Committee E30 on Forensic Sciences meets Feb. 10-11 in Atlanta, Ga. For meeting or membership information, contact Gloria Collins, manager, ASTM Technical Committee Operations (phone: 610/832-9715). //

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