This data from Google illuminates one of the biggest problems with self-driving cars

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Now, no company has perfected self-driving cars yet. But Google is generally considered one of the leaders in the space.

The company’s cars have driven more than 1.3 million miles since 2012 and have only been in a handful of accidents, none of which its vehicles were responsible for.

But as the data shows, its cars are still not 100% autonomous either — far from it, it seems. And that doesn’t bode well for Google in getting its technology to market anytime soon because Google only wants to sell fully autonomous vehicles.

This desire to only sell fully autonomous cars could be a weakness of Google's system compared to its rivals in the space like Tesla and General Motors, which are gradually making their cars fully autonomous by rolling out semi-autonomous systems in stages over a period of time.

For example, Tesla’s Autopilot feature enables its cars to get more self-driving capabilities with every software upgrade. The latest update gave Tesla’s Autopilot equipped cars a new function called Summon, which enables the car to drive by itself to the driver for very short distances while on private property.

Google has made it clear that it's not a fan of this approach and only wants to take fully autonomous cars to market. 

“The industry has been making continuous incremental gains, but for self-driving cars to reach their full potential we need to focus on nothing short of full autonomy,” John Krafcik, chief executive of Google’s self-driving car division, said on Tuesday at the Detroit Auto Show.

A big reason Google aims to make its cars fully autonomous right off the bat is because it sees semi-autonomous systems as a possible liability. Their concern is people trust technology too much and a system that only partially controls the car could endanger their life. 

For example, when Tesla first rolled out Autopilot, there were numerous YouTube videos that showed drivers testing the limits of Autopilot by taking their hands completely off the wheel while driving at fast speeds down a highway. One driver even sat in the back seat while the car drove itself down a freeway.

Now, Tesla and other car makers implementing these advanced drive assistance systems (ADAS) have always maintained that drivers are still required to monitor the driving situation and keep their hands on the wheel. But the fact of the matter is, once people get use to the technology, they will find ways to abuse it.

Google wants to avoid this, but by doing so they are possibly putting the company at a huge disadvantage because other car makers are beating them to the punch by rolling out features in stages.

On the plus side, the Google's system is getting better. The company says by late 2014 its autonomous systems disengaged every 785 miles, but by the end of 2015 that number fell to disengagements every 5,300 miles.

"Our objective is not to minimize disengagements," Google said in the report. "Rather, it is to gather, while operating safely, as much data as possible to enable us to improve our self-driving system. Therefore, we set disengagement thresholds conservatively, and each is carefully recorded."

What's more, regulators in California, where Google is doing the majority of its testing, have already made it clear that they aren't going to agree to fully autonomous cars for public use anytime soon. And as more states begin to pay more attention to the space, they are likely to follow in California's footsteps in implementing similar regulations and policies. 

We'll have to wait and see if Google budges on its approach, but for now it looks like it could be awhile before its fully autonomous cars take to the street in any meaningful way.