California Gov. Jerry Brown, front left, rides in a driverless car to a bill-signing at Google headquarters in Mountain View, Calif., in September 2012. Google has been developing autonomous car technology. (Eric Risberg/AP)

Imagine almost bumper-to-bumper traffic speeding around Washington’s Capital Beltway at 60 mph. A ridiculous notion now, but in a world when cars drive themselves, it may not be far-fetched.

There is, however, a hitch, and it points to larger issues that must be resolved before the dawn of the era of the autonomous vehicle.

Laws about what is a safe distance between vehicles differ from one state to the next. Many states simply say that they should keep “reasonable and prudent” distances, while others specify a certain distance based on how fast the vehicle is moving.

Enter the concept of “platooning,” the idea that two or more autonomous vehicles can travel in the slipstream of each other. As the Competitive Enterprise Institute points out in a report released Thursday, grouping vehicles almost bumper to bumper at highway speeds will reduce congestion, improve fuel economy and accommodate more traffic without requiring new highway lanes.

[Who should take the wheel in regulating driverless cars?]

The question of how closely automated vehicles can travel raises two of the larger issues that federal and state officials are working to resolve. With the advent of self-driving cars, there is greater need for uniformity in state traffic laws. There also is a delicate question: states traditionally have regulated drivers, while the federal government has governed vehicle safety.

Who takes the lead in regulating a system where one day drivers may rarely, if ever, touch the wheel?

Christopher A. Hart, chairman of the National Transportation Safety Board, said the issue requires collaboration on the federal and state levels.

“I think people are wildly underestimating the complexity of bringing automation into the system,” Hart said in a talk this month. “It will not end up as a patchwork quilt of, [in] this state, you have to have your hand on the wheel, [in] that state you don’t have to. There’s going to have to be some uniformity across state lines.”

A milestone in the road to autonomous vehicles is expected in the summer, when the U.S. Department of Transportation is to release its much-awaited guidance on the subject. Federal officials find themselves in a delicate situation, cautioned by those developing autonomous vehicles against premature regulations that might inhibit their progress but aware that without some guidelines, both state laws and technological advances may end up at odds with one another.

“The idea here is to try to avoid a conflict between safety and innovation,” said a federal official involved in creating the guidelines but not authorized to speak publicly about them. “You want people to be able to do this safely, but in an innovative manner.”

The guidance is intended to provide parameters for development without the strictures of regulation.

[White House hopes to shape national policy on driverless cars]

Blair Anderson, deputy administrator of the National Highway Traffic Safety Administration, said the guidelines also will include model state policies that seek to avoid a “patchwork of different rules,” and an attempt to clarify the state and federal roles.

“We’re interested in maintaining that traditional line: If it’s the hard vehicle, whether that’s the software in the vehicle or whether it’s the actual mechanical elements of the vehicle, NHTSA will continue to regulate that,” Anderson said last month in speaking to state officials in the I-95 Corridor Coalition, which represents 16 states and the District of Columbia.

States would continue to regulate the licensing of drivers, registration and other aspects, he said.

“We call it a model state policy. We don’t have any expectation that every state must implement each one of these provisions that we’re putting out there,” he said.

The other federal official said the point of the guidance is “to say here are the expectations, and really fill in the details as manufacturers go forward with this.”

“This is one of the tricky parts about trying to give guidance,” he said. “When people say automated vehicles, they may mean this highway auto­pilot that takes over for me, or a completely unmanned vehicle that can either transport people or goods in the middle of the city. And if vehicles are different in terms of their design domain, how is that communicated to the driver or owner or passenger if they’re not actually driving?”

The guidance is expected to provide a framework for automakers and touch on their responsibility for cybersecurity.

“Now, this is not at the level yet of setting standards or rules, but it’s really providing the framework for future discussion and development. What are the expectations?” the official said. “There will be concrete next steps.”

The document also is anticipated to restate NHTSA’s current recall mandate to cover recalls of autonomous vehicles.

“Our responsibility is for safety on the roadways, and we can say ‘We’re going to recall that because we believe there is a serious safety defect,’ ” he said.

And the final question to be addressed, he said, is whether federal regulators need to ask Congress for new tools to regulate the emerging industry.

“Guidance is not going to be the last step,” the official said. “It’s a way of having the conversations and identifying what are the important conversations that need to take place.”