Self-driving car advocates often note that more than 90 percent of serious accidents result from driver error, and thus estimate that autonomous cars will reduce fatalities by 90 percent. Indeed, in 2008 a National Highway Traffic Safety Administration (NHTSA) study of crashes between July 2005 and December 2007 found that 5,096 were caused by driver error, while just 130 were caused by vehicle failure and 135 were caused by the weather.

After some adjustments, NHTSA concluded that 93 percent of accidents can be attributed to driver error. So it seems reasonable to conclude that self-driving cars will save more than 31,000 lives per year (i.e., about 93 percent of the 33,560 fatalities suffered in 2012).

Not so fast, says a group called the Casualty Actuarial Society. It took a close look at NHTSA’s 2008 study and found that “49% of accidents contain at least one limiting factor that could disable [autonomous vehicle] technology or reduce its effectiveness.” That means self-driving cars will only reduce fatalities by about half, not 90 percent. While 16,000 lives saved per year is nothing to complain about, there’s a big difference between 16,000 and 31,000.

A close look at the Actuarial Society’s data (summarized here), however, provides more grounds for optimism. First, of the 49 percent of accidents that self-driving cars supposedly won’t prevent, 32 percent of them (about two-thirds of the 49 percent) would supposedly result because the drivers were too stupid, too inebriated, or too “aggressive” to actually use the self-driving option and insisted on taking control themselves. “Drivers who state they ‘always drive aggressively’ may choose to drive themselves,” says the summary.

The Antiplanner doesn’t buy this reasoning. While I understand that “100 percent adoption does not equate to 100 percent use” (at least initially), no one says that seat belts don’t save lives because not everyone uses them. Seat belts do save lives if people use them, and self-driving cars will save lives if people use them.

The study blamed another 12 percent of “driver-error” accidents on inclement weather. “Currently, automated vehicle technology cannot operate in inclement weather,” so the study assumes the driver would take over and suffer the same accident as a non-self-driving car. However, there are only some kinds of inclement weather than self-driving cars currently can’t handle (mainly snow and ice that obscures lane stripes), and there’s every reason to believe they will be able to handle such problems by they time they are introduced to the market.

Another 12 percent of accidents were found to be associated with vehicle or infrastructure problems such as braking deficiencies, traffic signal failure, or potholes. While these weren’t usually the main cause of accidents, they could contribute to accidents even of self-driving vehicles. However, if the accident is caused by vehicle failure, it isn’t due to driver error.

In short, nearly all of the driver-error accidents that the report says self-driving cars won’t prevent are due to drivers taking over from the self-driving car. But the long-run vision for autonomous vehicles is vehicles than have no option for drivers to take over. So, in the long run, self-driving cars really will reduce accidents and fatalities by around 90 percent.

In related news, the Antiplanner’s argument that self-driving cars would eliminate the need for mass transit in most cities was reported by Congressional Quarterly’s Roll Call news service. But another report by the same writer focused on an answer I gave during the Q&A session of last week’s policy forum.

Asked what effect self-driving cars would have on local governments that get a high percentage of their receipts from traffic tickets, I noted that not only would those governments have to find another revenue source, but hospitals will need to find another source of organ transplants as some 70 percent of organs come from victims of traffic accidents. While that’s not necessarily a bad thing, an advertising firm called Sparks & Honey put a more positive spin on both effects.

Page 43 of the firm’s 62-MB presentation on self-driving cars notes that such cars will allow us to “enjoy more efficient government” because local government will have to cut budgets in response to declining ticket revenue. Page 38 says “we will see a surge in 3D printed organs” because organs available for transplant will decline. The 52-page presentation makes a number of other interesting predictions, most of them positive, though it predicts that self-driving cars will lead to more substance abuse because people won’t need to stay sober to drive.

Economically, a change that forces people to adopt new technologies (such as 3D printed organs) isn’t always a good thing if that new technology is more expensive than the old. But when you combine the high cost of organ transplants (including the high risk of rejection and the lifestyle changes imposed on recipients in order to minimize rejection) with the fact that 70 percent of organ transplants require someone’s death in a vehicle accident, then an alternative, if it can be found, is probably worthwhile.