By Michael Barr
Note: This article summarizes a public regulatory and court record. It is general commentary for engineers and litigators, not legal advice.
Toyota sudden unintended acceleration, or SUA, is the most important software safety story in the history of cars. In the 2000s, Toyota switched from a mechanical gas pedal to an electronic one that is run by software. Some drivers said their cars sped up on their own. Toyota blamed floor mats and sticky pedals. Regulators investigated. Then, in 2013, an Oklahoma jury decided that a flaw in the car's software had caused a deadly crash. This page is a short summary of that public story, with links to the key documents that are still online.
The public story
The complaints and recalls. All through the 2000s, more and more Toyota and Lexus drivers reported cars that sped up on their own. By 2010, federal regulators had linked dozens of deaths to these runaway Toyotas. Toyota recalled millions of cars, but it blamed the problem on floor mats that could trap the pedal and on pedals that could stick. Both are mechanical causes, not software.
The government's review. Under heavy pressure from Congress and the public, the government studied Toyota's electronic throttle, with help from NASA engineers. Working fast, in about ten months, that 2011 review did not find an electronic cause for the sudden acceleration, and regulators stuck with the floor-mat and sticky-pedal explanations. The reports were careful, and they are still the official government record. But the review was rushed, and it did not dig into the software the way later court cases would.
The software examined at trial. The Bookout case came out of a 2005 Toyota Camry that sped up on its own and crashed. One woman died, and the driver, Jean Bookout, was hurt. The plaintiffs argued that the real cause was Toyota's software. But almost no one was allowed to look at that software. The source code was kept secret under a court order, and only about a dozen people ever saw it. The jury was not among them. Instead, a team of software experts led by Michael Barr studied the code, with more time than the rushed government review had. Mr. Barr then explained to the jury, in plain terms, what he had found.
He described how a key part of the software, the part that controlled the throttle, could stop running if the computer's memory was corrupted. When that happened, the safety checks that were supposed to catch the problem were not good enough to stop it. And the code was so large and tangled that mistakes were easy to miss. The press called it the "spaghetti code" testimony. The judge let the jury hear it, over Toyota's objection, and the jury decided that flaws in Toyota's software had caused the crash. Toyota settled soon after the verdict. It also paid about 1.5 billion dollars to settle a separate class-action lawsuit.
Why it still matters
Toyota SUA is the case that finally opened up software in court. It showed, on the public record, that experts can dig into a car's hidden source code, find out how it can fail, and explain that to an ordinary jury. It proved that a bug buried deep inside software can be shown to cause real harm. For engineers, it is still the go-to example of why safety-critical software has to be built carefully, with real safety checks, clear coding rules, and code that is simple enough to actually test.
Key documents and coverage
- Michael Barr's trial testimony transcript (redacted), his testimony in Bookout v. Toyota, archived by Safety Research and Strategies.
- The 2011 NHTSA and NASA technical reports, the U.S. Department of Transportation release of both government engineering reviews of Toyota's electronic throttle control system.
- Killer Apps: Embedded Software's Greatest Hit Jobs, Michael Barr's keynote on the public lessons of this and other cases.
- Toyota Unintended Acceleration and the Big Bowl of "Spaghetti" Code, Safety Research and Strategies' detailed account, which also archives the trial exhibits and slides.
Barr Group's role
The software work at the heart of the Toyota SUA cases was led by Michael Barr. It shows how Barr Group's software and electronics expert witnesses work. They review the source code under the court's protective order, tie every finding to the code itself, and explain it clearly enough to convince a jury and hold up under tough cross-examination. You can read a short version in our Toyota case study, and more about how we run a review in our guide to vetting a source code review team.
The takeaway
The Toyota cases made one thing clear: software bugs are not beyond proof. With the right experts, the right access to the code, and the ability to explain what the code really does, a flaw hidden inside a safety-critical system can be found, explained, and proven in court.
Barr Group's team of electronics and software expert witnesses provide experienced and unbiased source code reviews, expert reports and testimony for product liability, patent infringement, software copyright, and trade secrets litigation involving computer-based technology and software. HIRE AN EXPERT