IIHS analyzes ‘redundant’ AV crash data, determines federal reporting system needs improvement

The federal system for monitoring automated vehicles needs improvement, according to a new study from the Insurance Institute for Highway Safety (IIHS).

Researchers found that, per vehicle miles traveled (VMT) during the study period, Waymo’s driverless vehicles were involved in 68% fewer crashes overall than human drivers. During the study period between 2021 and 2024, Waymo vehicles operated in San Francisco, Phoenix, Los Angeles, and Austin. IIHS notes that the sample was restricted to crashes that a person would typically report to the police.

“The results show that, on a limited scale, these driverless cars are safer than human drivers — who can be impaired or drowsy or suffer lapses in attention,” said IIHS President David Harkey in a press release. “However, the present data collection system isn’t good enough to allow continuous monitoring of a large-scale expansion.”

The IIHS researchers estimate that only 22% of the 736 public-road crashes that were reported in which automation was engaged were likely police-reportable — 89 crashes involving Waymo vehicles, 50 involving Cruise vehicles, 10 involving Zoox vehicles, and 10 involving other companies. Because mileage data was only available for Waymo, they used its crashes to calculate self-driving vehicle crash rates. Of Waymo’s 89 police-reportable crash involvements, 64 were in driverless operation, and the others involved supervised use of the automation.”

Waymo began its driverless robotaxi service for the public in Phoenix in 2020 following its 2009 launch as a Google self-driving car project. It then expanded to San Francisco in 2022 and Los Angeles in 2023. Limited operation began in Austin in 2024. Its vehicles are classified as Level 4 on the automation scale created by SAE International, which means automation can handle all the driving with no human supervision under certain conditions.

In contrast, the Level 2 partial automation systems widely available for purchase by the general public, such as General Motors’ SuperCruise or Ford’s BlueCruise, require a human driver to remain alert and ready to take over at all times. IIHS says those systems involve different risks: the monotony of supervision can lead to attention fatigue, and many drivers put too much trust in the technology.

“Level 3 systems can operate without constant human supervision in specified conditions, but a human still needs to be in the driver seat and ready to intervene when requested,” the release states. “Vehicles with such systems are very rare. Level 5 vehicles, capable of driving without human input under all conditions, do not yet exist.”

According to IIHS, since 2014, California has required companies testing self-driving cars on public roads to report crash involvements that result in fatalities, injuries, or property damage of any amount. The National Highway Traffic Safety Administration (NHTSA) began requiring similar reporting in 2021 under a Standing General Order (SGO) on crash reporting for incidents involving automated driving systems.

“While the SGO database was primarily intended to track defects and enforce recalls, it is the only national data collection tool for crashes involving self-driving vehicles,” IIHS states in the release. “For this reason, it is a key resource for safety research. However, neither it nor the California database makes it easy to compare the crash rates of Level 4 vehicles with those of human drivers.

“While companies are required to report crashes, they are not obligated to report the miles they log or whether such miles involved a human driver. Waymo provides driverless VMT information voluntarily, but other companies do not. That makes it impossible to know how common it is for their vehicles to crash.”

However, IIHS researchers found that, even with the mileage data that Waymo provides, a direct comparison with human crash rates is impossible without time-consuming operations to account for differences between the reports required by the SGO and what humans report.

“Human drivers are generally only required to report crashes that cause an injury or result in more than $1,000 in property damage to the police, though the damage threshold varies by state,” IIHS says. “Many drivers also opt not to report crashes that meet the reporting threshold to avoid an increase in their insurance premiums or for other reasons. Around half of all crashes and a third of injury crashes go unreported.

“In contrast, until an amendment to the SGO that took effect in 2025, self-driving vehicle companies were required to log minor incidents as crashes. For example, a vehicle scraping its undercarriage as it turned into a parking lot would count as a crash. Though the property-damage thresholds are now more closely aligned, companies are still more likely than regular people to report all qualifying crashes due to the business risks of failing to comply with the regulation. Moreover, driverless vehicles require expensive sensors that can be damaged by minor impacts, making their crashes more likely to exceed the damage threshold.”

IIHS researchers said that to complete their research, they needed a realistic comparison of crash rates submitted to NHTSA by Cruise, Waymo, Zoox, and others from 2021 to 2024.

“The first step was to cull hundreds of redundant records,” the release states. “They also needed to eliminate certain incidents. These included situations in which the automation wasn’t engaged, the vehicle wasn’t on a public road, or no real crash took place. This process eliminated about a quarter of the reported crashes.”

Next, researchers had to determine whether the reported incidents were severe enough that a reasonable person would have reported it to the police. To do so, they analyzed crash impact and property damage, the types of injuries reported, and other factors.

“For example, if a person complained of pain but left the scene, the researchers coded that crash as unlikely to be reported to the police,” the release states. “If an airbag deployed, they coded that crash as police-reportable due to the higher impact speed and the cost of airbag replacement — regardless of other property damage or injury.”

The researchers also found that Waymo vehicles traveled about 50 million miles in driverless operation over the study period, compared with about 222 billion miles by human drivers during the same time period and at the same locations.

“Overall, Waymo’s crash involvement rate was 68% lower than that of human drivers — 76% lower in Phoenix, 35% lower in San Francisco, 71% lower in Los Angeles, and 4% higher in Austin, where the sample size was relatively small,” the release states. “Waymo vehicles were involved in 85% fewer single-vehicle crashes and 81% fewer injury crashes per VMT than human drivers.”

Eric Teoh, IIHS director of statistical services and lead author of the study, said the study shows “encouraging signs for the future of driverless vehicles.”

“Now we need to get the data collection system right, so that we can ensure that level of safety continues as these technologies become more prevalent,” he said in the release.

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Featured image provided by IIHS