How does a police officer pull over a driverless car?

In Pittsburgh, Uber began testing self-driving cars with technology that includes cameras like these.Angelo Merendino/AFP/Getty Images

Within a single week, the City of Boston announced it would soon allow testing of self-driving cars on its hectic streets, the federal government unveiled its guidelines to allow them on the nation’s roads, and a small fleet of them began zipping around Pittsburgh.

The flurry of activity made clear that the era of robocars isn’t a far-off future. But it also exposed a hole in Massachusetts law: It does not say anything about self-driving technology, leaving law enforcement and Massachusetts officials struggling to say whether a fully driverless vehicle would even be allowed today on the state’s streets.

Boston officials hope to begin testing on city streets before the end of the year.

Massachusetts State Police spokesman Robert Lima said troopers would be inclined to pull over a driverless vehicle, “on a case-by-case basis due to public safety.”

Mark Leahy, executive director of the Massachusetts Chiefs of Police Association, expected local police officers would do the same, possibly for “driving to endanger.”

“I’m quite confident that, at the bare minimum, the person in the passenger seat would have to take over,” Leahy said.

Meanwhile, the Massachusetts Department of Transportation said state law does not prevent the operation of an autonomous vehicle, so long as it and the driver are properly licensed, inspected, and equipped.

However, said spokeswoman Jacque Goddard, “given our understanding of current technology, we believe a vehicle operating in fully autonomous mode should be operated with a seated driver, so as not to violate driving laws and to ensure the safety of the public.”

And in the Legislature, Representative William Straus, cochair of the Joint Committee on Transportation, said he does not believe it is illegal for self-driving cars to be road-tested today in Massachusetts. Nonetheless, he said, it would be “prudent” to hold off on the experiments — including the upcoming Boston tests — until legislators clarify the law.

“If, God forbid, something bad should happen on the public ways as a result of an error or something going wrong with one of these vehicles, the existing statutes don’t fully take account of them in terms of liability, both civil and criminal,” Straus said.

Already though, there is conflict between Massachusetts regulations and where some of the driverless technology is heading. For example, state vehicle inspection requirements assume every vehicle has a steering wheel and a brake pedal. But Google’s prototype driverless car has neither, suggesting it could not pass inspection in Massachusetts.

Self-driving cars are not explicitly legal in In Pennsylvania or Washington state, either. Yet with the blessing of officials in each state, Uber last week launched its experiment, with autonomous Ford Fusions scooting around Pittsburgh, while Google has been testing its car in Kirkland, Wash.

Before it began testing driverless cars in Pittsburgh, Uber sent vehicles with systems to map the roads and topography to roam the city’s streets. Jeff Swensen/The New York Times

For now, those experiments have a human in the driver’s seat ready to take control.

And already, some cars on Massachusetts roads are equipped with “semi-autonomous” features. Tesla’s controversial autopilot system can keep a car in its lane but requires drivers to pay attention and be ready to take control.

But down the road, cars could become fully driverless, without even a steering wheel. The federal government is preparing for that future.

This week, the Obama administration issued guidelines that dictate the government will oversee safety and the technologies that allow vehicles to operate on their own. States would still oversee issues like insurance, law enforcement, and registering and inspecting vehicles. But the administration encouraged states to adopt model policies to minimize differences across the country.

Bryan Reimer, associate director of the New England University Transportation Center, urged Massachusetts to establish a clear framework for testing the vehicles because that could make Boston a center for the industry, given the region’s status as a robotics powerhouse.

Boston officials said they would not allow the testing of self-driving cars until they have the state’s blessing.

Kris Carter, cochair of the Mayor’s Office of New Urban Mechanics, said that while the city does not necessarily need a green light from the state, officials from both governments will work “hand in hand” to address various questions before the testing begins.

Boston is conducting the experiment in partnership with the Switzerland-based World Economic Forum and Boston Consulting Group.

John Moavenzadeh, the World Economic Forum’s head of mobility services, said that relevant state regulations will be followed during the testing and that Boston was chosen, in part, because of the good working relationship between city and state officials.

A driverless Uber car’s monitor showed a 3-D mapping of what the vehicle’s cameras see during a test drive in Pittsburgh. Jeff Swensen/The New York Times

So far, Boston officials have offered few specifics on the testing; Carter, for example, declined to say if the city will require the driver’s seat to be occupied, as in road tests elsewhere.

Xanthi Doubara, a consultant at Boston Consulting Group, said it is “very, very likely” that Boston will follow the practices of other experiments, which include having someone in the driver’s seat and limiting the testing area to a section of the city at the start.

But if Boston officials were to wait for the Legislature to act, testing would be unlikely to get underway this year. Lawmakers have already adjourned for the 2016 formal session.

Bills that would allow the testing of driverless cars were introduced in both legislative chambers. One that passed the Transportation Committee would have required an operator in a driverless car, ready to take control, unless the test occurred on a closed course.

Straus predicted the Legislature will be eager to take up driverless cars next year.

“It’s likely to be an important priority for the Legislature because it’s an important safety issue for the public, and obviously, given the Boston announcement, it’s an important economic development issue for the state,” Straus said.