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A letter from the National Highway Traffic Safety Administration (NHTSA) to Google has opened the door for the tech giant’s self-driving car system to be legally viable on US roads.

The letter, from NHTSA chief counsel Paul Hemmersbaugh to Google self-driving car chief Chris Urmson, grants “several” of Google’s requests for interpretation in terms of braking, vehicle controls and displays, and rear visibility among others.

The key issue, according to the NHTSA, is that the majority of the road rules laid down in terms of cars needing steering wheels, the definition of a ‘driver’ and so on, will be potentially ripped up by Google’s system. Yet the administration is willing to make compromises if necessary.

“We agree with Google its SDV (self driving vehicle) will not have a ‘driver’ in the traditional sense that vehicles have had drivers during the last more than one hundred years,” the letter reads. “The trend toward computer-driven vehicles began with such features as antilock brakes, electronic stability control, and air bags, continuing today with automatic emergency braking, forward crash warning, and lane departure warnings, and continuing on toward vehicles with Google’s SDV and potentially beyond.”

So does this mean it is only a matter of time before Google’s system is waved through? NHTSA insists this is only an interpretation, rather than a hard ruling, and asks Google to provide more evidence in various cases.

“NHTSA recognises that it can take substantial periods of time to develop some rulemaking proposals and final rules, including time spent obtaining review of those proposals and seeking and analyzing public comments,” the letter continues. “NHTSA further understands that the time it takes to conduct rulemakings may, in some instances, make such proceedings ill-suited as first-line regulatory mechanisms to address rapidly-evolving vehicle technologies.”

Earlier this year, Google reported 13 accidents and 272 failures in its self-driving cars in the 14 months ending December 2015, but noted that failure rate was slowing down over time. In November, a research note from IHS Automotive claimed Google was the current technological leader in self-driving vehicle development.

You can read the full NHTSA letter here.