By now, I’m sure that almost everyone has heard about the vehicle recall and attendant problems that Toyota has been having in the last few months. I’ve posted a couple of notes here, about the difficulty of finding flaws in a very complex system, and about the possibility that software bugs might be responsible. In the last few days, there have been some intriguing further developments in this story.
Toyota has consistently maintained that the problem (of unintended acceleration) is not due to any flaw in its electronic throttle controls. This claim has been regarded with some skepticism (including mine), because finding problems in systems as complex as this is not easy. To underscore this point, the New Scientist has an interesting article summarizing some of the many ways in which electronic controls are used in today’s automobiles. There are many control subsystems, which are linked together using a “data bus” network. One of the questions raised in the article is whether that bus, or the electronic components themselves, can malfunction if data is corrupted by some external influence, such as electromagnetic interference [EMI]. According to the article, there is at least one case of this affecting vehicle anti-lock braking systems:
During the 1980s, drivers of Mercedes-Benz cars with anti-lock brakes (ABS) reported that their brakes were failing on a section of autobahn in the Saarland region of Germany. The problem, caused by electromagnetic interference (EMI) from a nearby radio transmitter, was solved by putting up a giant wire mesh by the side of the road to shield traffic from its radio transmissions.
There have also been documented cases of EMI causing problems with remote locking and security systems.
As if terrestrial sources of EMI, like radio transmitters, were not enough, a recent article at Live Science suggests that another possible cause of Toyota’s problem is cosmic rays. This is actually not as goofy as it might at first sound. As modern digital electronics have gotten smaller and more densely packed (Moore’s Law, and all that), they are representing each bit of data with a smaller electric charge. As the charge gets smaller, it becomes more susceptible to being disrupted by highly-energetic particles, like those associated with cosmic rays. It’s well known in the aerospace industry, for example, that radiation can “flip” individual bits in semiconductor devices. Some types of devices, those that are “field programmable”, are especially vulnerable, because they store not only their data but also their basic logic in memory (somewhat analogous to microcode). It’s not at all clear how much, if any, of this has been evaluated in the context of automobiles.
Fortunately, the problem has festered long enough that some additional expertise is to be brought to bear. According to a Reuters report carried by the Washington Post, scientists from NASA have been asked to assist the National Highway Traffic Safety Administration [NHTSA] in analyzing the electronic throttle controls used by Toyota. Additionally, Transportation Secretary Ray LaHood has asked the National Academy of Sciences to conduct a study of unintended acceleration across the auto industry. This is a welcome development. I am sure that the engineers at the NHTSA are very good at analyzing the effects of traffic conditions and wet pavements on accidents, it is less clear that their expertise extends to finding flaws in complex software systems. As we become increasingly dependent on technology in all phases of life, we mustn’t let petty things like inter-agency rivalries to get in the way of solving problems.