Self-driving cars that still look and feel like a traditional vehicle face relatively few regulatory and legal barriers. But strip out the steering wheel and foot pedals or drift too far from a conventional vehicle design and they will come up against significant restraints, says a preliminary report released Friday by the U.S. Department of Transportation.

In short, the federal government isn’t prepared to regulate or certify Google’s self-driving prototype—or any other conceptual vehicle that isn’t equipped with standard manual controls.

The report says self-driving cars that begin to push the boundaries of conventional design would be constrained by current federal motor vehicle safety standards. The basic problem is that the standards are based on the assumption that vehicles would always have a steering wheel, foot pedals, or even a rear visibility. Regulators must now figure out how to certify a car that might have seats designed like a lounge and that may not even face forward.

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The DOT and the National Highway Traffic Safety Administration is working diligently to catch up to the technology developed by Google, tech companies like GM’s recent acquisition Cruise Automation, and other automakers. In January, DOT Secretary Anthony Foxx gave his agency six months to develop operational guidelines for how automated vehicle technology should be tested and regulated, as well as a model policy for states to help end the mishmash of rules that threaten to slow down the development of self-driving cars.

A patchwork of rules is already developing in states, notably in California where numerous companies, including Daimler and Google, are testing self-driving car technology on public roads. In December 2015, California’s Department of Motor Vehicles issued draft rules in an effort to address the thorny questions involving autonomous vehicles around licensing, registration, certification, and safety—they even addressed cyber security and privacy. The draft rules include strict limits on the emerging technology, a position Google has said will place a ceiling on the potential for fully self-driving cars.

For instance, California’s rules prohibit the use of fully autonomous, driverless cars that don’t have a steering wheel or a brake pedal—like the prototype that Google has developed. A licensed operator must be present inside the vehicle and be capable of taking control at all times, if the technology fails or there is another emergency.

But the hope is that the DOT’s operational guidelines will help states like California and Nevada (another active testbed for the driverless technology) navigate the legal, safety, and regulatory obstacles without slowing the pace of innovation.

The DOT says it wants to release those guidelines by July. On Friday, the agency said it will hold two public hearings on autonomous vehicles to get feedback. The first will be Apr. 8 in Washington D.C., according to NHTSA spokesman Gordon Trowbridge. A second hearing will be held at a later date in California.

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Federal regulators have already made one critical decision about self-driving cars. In February, the NHTSA said that the artificial intelligence system that controls Google’s self-driving car can be considered a driver under federal law. The legal interpretation by federal regulators was made in response to a November petition from Chris Urmson, the director of Google’s self-driving car project.

While this is a critical first step towards Google’s goal of commercializing self-driving cars by 2020, it doesn’t mean fully autonomous vehicles are legal for public use. The next question is whether (and how) Google could certify that the self-driving system meets standards that currently apply to vehicles with a human driver. And that’s a process the feds will have to drive.