They look like tricked-out wheelbarrows, hit speeds up to 40 mph and produce zero emissions. Made by a company called ZAP (from 'Zero Air Pollution') the mini electric cars and trucks can carry up to 500 pounds and plug into a standard household outlet to recharge. You can spot the little runabouts in urban centers across the United States, but not everywhere.

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In roughly a half-dozen states, ZAPs are not yet legal. Federal law classifies them as motorcycles, which relieves them of the same safety regulations as cars and trucks. In Massachusetts, that definition doesn't gel with laws that state no vehicle with an enclosed cab can be a motorcycle, and the state Registry of Motor Vehicles has reservations about putting the tiny ZAPs out on Bay State roads.

"Nations all over the world are churning out these vehicles quicker than we can even determine what they are," said registrar Rachel Kaprielian of the Massachusetts Executive Office of Transportation. "No matter what we call it, no matter how much smaller they get or how much faster they get or more innovative they get, it still comes down at the end of the day, is this safe?"

The confusion has left one Bay State ZAP owner in legal limbo. Doug Hart was the first person in Massachusetts to purchase a ZAP Xebra in 2006.

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"In all honesty, it's just a golf cart on steroids but, it's great around town,” Hart said about his ZAP Xebra four-door sedan. “It only goes 25 miles before it needs to be recharged overnight, but that's fine for weekends, going to the store, clothes dropped off, that sort of a thing."

After two years of driving, Hart’s errand-running hit a road block. The state revoked his registration citing safety concerns. Registry officials fear irresponsible owners will take the slower vehicles on highways, causing accidents.

"I'm tremendously frustrated because it's become a driveway ornament instead of something i can actually use," said Hart.

Massachusetts lawmakers are pushing for a variety of new rules to help get these so called "city cars" on the roads. Among the suggestions: posting minimum speed signs or creating road restrictions, allowing ZAPs to drive on city streets only.

At the ZAP world headquarters in Santa Rosa, Calif., executives are working with state and local officials to pass new laws. "The federal government has approved our vehicles on a national level and there are a few states getting left behind," said ZAP CEO Steve Schneider.

Over the past year, sales of ZAP vehicles have increased 200 percent. The company is in the process of moving their production facilities from China to a new site in Kentucky.

With the fluctuating price of gasoline, many consumers are seeking smaller, more fuel efficient vehicles, inspiring inventors to create a plethora of new-fangled rides. ZAPs are some of the first, but they won't be the last to hit legal roadblocks as states struggle to balance safety with innovation.

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Molly Line joined Fox News Channel as a Boston-based correspondent in January 2006.