Geohot said on Twitter that the special order opened "with threats" rather than an attempt at dialogue. "Would much rather spend my life building amazing tech than dealing with regulators and lawyers," he tweeted just before officially canceling the Comma One. "It isn't worth it."

The comma one is cancelled. comma.ai will be exploring other products and markets. Hello from Shenzhen, China. -GH 3/3 — comma ai (@comma_ai) October 28, 2016

The letter and special order sent to Geohot by the NHTSA outlined the administration's role in overseeing the safety of motor vehicles and asked for detailed answers to 15 questions about how the Comma One would work.

"We are concerned that your product would put the safety of our customers and other road users at risk," the letter said. "We strongly encourage you to delay selling or deploying your product on the public roadways unless and until you can ensure it is safe."

The NHTSA asked for Geohot to submit his answers by November 10th. The one line that could reasonably be construed as a threat, as Geohot called it, was the following: "If you do not timely or completely respond to the Requests in the Special Order, you may be subject to civil penalties of up to $21,000 per day." The letter closes with contact information for a member of the NHTSA legal staff.

When Geohot revealed the Comma One in September, we were impressed but understandably skeptical. His company, Comma.ai, seemed to be moving remarkably quickly -- perhaps that's because Geohot skipped some of the standard paperwork.