It's Oct. 21, 2015. That means the future - as envisioned in the 1989 film Back to the Future II - is officially here.

As predicted, we do indeed have flat-screen TVs, video conferencing, and drones - and, appearing on Philadelphia streets of late, a device vaguely resembling Marty McFly's hoverboard.

For now, though, Kevin DiCesare still tends to turn heads while cruising in the Spring Garden Street bike lane during his daily, eight-mile-round-trip commute on a Ninebot One, a device that might best be described as the uncanny love child of a unicycle and a Segway.

Is this the commute of the future? DiCesare thinks so.

"You can't always say you love going to work," he said. "But this is an adventure every morning."

It's one of many ways a growing number of Philadelphians are using a new breed of transportation technology that has rolled onto city streets, sidewalks, and bike lanes faster than the speed of regulation. That includes the two-wheeled, Chinese-made electric scooters whose viral popularity - particularly among teens and college students - can be traced back to products well placed with celebrities from Justin Bieber to Wiz Khalifa.

The appeal is obvious. The legal question is a little more confusing.

It has been about three months since DiCesare got his device, which, for lack of a catchier term, he has been calling a "hoverwheel."

He was looking for a new way to get from his Fishtown home to his data-management job near 19th and Market. Bicycling left him too sweaty. And he was frustrated with SEPTA's Market-Frankford Line, which runs skip-stop service during rush hour. "That's made me late for work many times," he said.

His Google search for "personal transporter" yielded the self-balancing, single-wheeled device that, starting at $650, is about one-tenth the price of a Segway and much easier to store under his desk at work. It goes about 13 miles per hour, getting him to work in 20 minutes.

"Now, I'm early every day," said DiCesare, who has been encouraging friends to follow his lead.

Still, being an emissary from the future can be difficult.

On the street, cars don't always give him a wide berth. And on the sidewalk, some passersby get annoyed.

"I did have a gentleman push me off of it because he was upset that I was riding on the sidewalk," DiCesare said. He and his hoverwheel suffered minor injuries.

As no one else he knew had one, he had to guess which laws might apply.

He decided to go by the state's relatively new regulations for electric-assist bicycles, which set a maximum speed of 20 miles per hour and engine power of 750 watts. "I felt I was in compliance with that law," he said, "being a bicycle or not."

He's sort of right.

Pennsylvania Department of Transportation spokesman Rich Kirkpatrick said legislators had not yet anticipated such a device as the hoverwheel.

"There are no specific state rules applied to one-wheeled self-propelled devices," he said. "We cannot speculate on possible local ordinances, or how law enforcement handles these situations."

Neither can DiCesare, who tried to cross the Ben Franklin Bridge twice - once successfully and once not. The first time, he said, "I met a Delaware River Port Authority officer at the halfway point. He liked it. He just told me to be careful." The following week, "I tried again," he said, "and I wasn't allowed."

The commonwealth's Motor Vehicle Code does provide for two-wheeled, self-balancing contraptions, under the rather unsexy moniker of "Electric personal assistive mobility device" or EPAMD.

Aside from banning them on freeways, Pennsylvania doesn't really regulate EPAMDs, Kirkpatrick said: "Any determination of whether such a vehicle is acceptable for street use is up to law enforcement."

A Philadelphia police spokesperson said the scooters would fall under city bicycle ordinances. That means riding them on Philadelphia sidewalks is illegal, unless you're younger than 12.

Still, that hasn't stopped a growing number of adults from trying it, inspired by the endless pool of hoverboard "fail" videos online, continued celebrity interest, and increased availability.

One Philadelphia company, Rollerboard, has begun marketing its own brand of the scooters, joining dozens of other brands flooding the market.

Sanjay Mukherjee, Rollerboard's CEO, said he had not tried to lobby for regulatory clarity. He figured his $995 product would fall under the same rules as a skateboard or bicycle, which he didn't realize were banned from most sidewalks.

"Until someone comes and says, 'This is illegal,' you can assume these are legal," Mukherjee said.

Drew Cooper, 15, who lives near Rittenhouse Square, bought one of the two-wheeled boards online three months ago, using birthday money and profit from selling his possessions on eBay.

He figured they're all the same boards rebranded - with names like ioHawk and Phunkeeduck - so he bought based on price. When his board arrived, a month and about $350 later, he was the first of his friends to have one.

He and his brother Luke, 12, have fallen off the board a collective three times. But they like to take turns riding it between their mother's and father's houses, four blocks apart. It's faster than walking - or would be if it weren't for the gawkers.

Luke, balanced atop the board in the middle of a quiet street, said he was used to ceaseless questions. "People, if we're riding it around, stop us and ask, 'What is it, and how does it work, and what's it called?'"

He's used to calling it a hoverboard, though the etymology of the word escaped him. Asked whether he had seen Back to the Future, he looked at his father quizzically.

"I'm not sure," he said, and he made another lazy figure-eight on his hoverboard.

smelamed@phillynews.com

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@samanthamelamed