The National Highway Traffic Safety Administration earned plaudits from across the tech sphere for its recently released safety guidelines for self-driving cars.

With the NHTSA looking to offer guidance to this emerging industry, the agency issued a set of rules that largely just asks manufacturers to report on how they were following the guidelines. The 15-point checklist is vague in quite a few details, but that isn’t necessarily a tremendous problem so long as the standards remain voluntary, which they purport to be. To many, this approach struck a good overall balance between oversight and flexibility.

Regulatory ambiguity can, however, turn out to be a real nightmare with standards that are mandatory. Vague rules can leave even the best-intentioned firms at a loss as to how to proceed. Given how much of a premium consumer confidence will be in a market as revolutionary and potentially transformative as autonomous vehicles, it’s crucial that manufacturers comply with whatever standards the federal government promulgates.

That’s why it’s essential to pay close attention to an underappreciated part of the NHTSA guidelines — the opportunities they afford federal regulators to coordinate with the states on oversight that, in practice, will be anything but voluntary. Indeed, the early signs from the first of what will be many proposed state rules to follow in the wake of the NHTSA guidelines suggests that compulsory standards are exactly what we’re going to get.

First up are proposed rules from the California Department of Motor Vehicles, recently revised in response to the NHTSA guidelines. The revised draft of California’s model regulations is far more permissive than the original version the agency promulgated late last year, a set of changes that were celebrated by various observers, even me.

But delve closely into the updated DMV proposal, and you’ll find a requirement that manufacturers obtain a state permit certifying that any and all vehicle tests are conducted in accordance with the NHTSA’s “Vehicle Performance Guidance for Automated Vehicles.” Thus, in the nation’s largest testing jurisdiction, the NHTSA standards already are set to be made mandatory.

This is not to say the federal government doesn’t have a role to play in oversight of self-driving cars. The feds are better situated to oversee the development of safety standards, and the door should be open to refine those standards. But coordinating with the states to turn those standards into a set of de facto binding obligations smacks of underground rule-making.

The California DMV might be complicit in this collusion, but it can’t be faulted for deferring to federal authority. Were the NHTSA’s safety standards clearer — an undertaking that presents risks and problems of its own — California’s approach wouldn’t actually be a problem. The fact that the federal guidelines are so vague in so many of the details means that we can’t really know either that manufacturers will be able to comply with California’s rules or that the state will be able to enforce them.

For now, state regulators should use their discretion to be as liberal as possible about what sorts of vehicle testing comports with the NHTSA safety guidelines. Over the longer term, what we need is for states like California to communicate to the NHTSA that it’s up to them to make absolutely clear what does and does not count as compliance.

It’s broadly understood how overly restrictive regulations can dampen innovation, but regulatory ambiguity can be just as bad. For regulators, the clock is ticking. It’s up to both the NHTSA and state agencies like the California DMV to bring the clarity this new market needs.

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