Google's self-driving vehicles have collectively logged millions of autonomous miles on public roadways. While the technology powering Google's cars is steadily improving, a recent report reveals that human intervention is still needed at times.

In a report filed Tuesday with the state of California, Google referenced 272 occurrences during a 14-month period in which a human driver had to immediately take over control of a self-driving car. Upon further investigation, Google determined that "contact" would have been made (presumably with another vehicle, a pedestrian or other nearby object) had a human not taken over in 13 of the 272 cases.

Data also revealed that Google has vastly improved its driving technology over the course of the project. As The Wall Street Journal notes, the number of disengagements dropped from once every 785 miles in the first quarter of testing to once every 5,318 miles in the most recent quarter.

In December, California proposed regulations that would require "drivers" of autonomous vehicles obtain a special license. Consumer Watchdog’s Privacy Project Director John M. Simpson praised the DMV for putting safety first, adding that the release of the disengagement report is a positive step. Simpson said Google should also make public any video it has of the disengagement incidents.

John Krafcik, the head of Google’s self-driving car program, reiterated on Tuesday that they're firmly committed to developing vehicles that require no human backup drivers.