TAMPA — Commuters who take the bus downtown are accustomed to letting someone else do the driving.

But before long, for a portion of their trip, they may have the option of letting no one do the driving.

Plans are under way for driverless shuttles — "autonomous vehicles" — running up and down the Marion Street Transitway in eastern downtown, a route restricted to buses and other public transit.

Two boxy electric vehicles carrying six to 12 passengers would run from the Marion Transit Center south to Whiting Street, a 0.6-mile stretch with 11 intersections.

An attendant would be on board, but the vehicles, now in use in cities including Phoenix and across Europe, are designed to "see" 360 degrees around them without human assistance, using lasers, radar and other sensors.

A test of the Marion Street system is scheduled for late next year.

Google, an industry leader in developing autonomous vehicles, said computer software can detect cyclists and pedestrians, which street and lane it's traveling in and what surrounding objects will do.

The Hillsborough Area Regional Transit Authority hopes the new shuttles will help provide one solution to its "first mile/last mile" challenge — how to get potential bus riders from their home and work to stops along the routes that buses travel.

"AV technology is coming," said Katharine Eagan, HART's chief executive officer. "Whether it's going to be in your new car, on your bus, or integrated into your phone, it's coming. The best way to be ready is to be at the forefront."

HART is developing the program with the state Department of Transportation, which has allocated up to $1 million for the project over the next two years. If its succeeds, there may be money for a third year.

A contractor will be hired to run the service.

Slightly larger than a minivan, the vehicles would have seating surrounding the door and a display of real-time bus connections. They would pass each point along Marion Street every 10 minutes, and anyone — not just bus patrons — would be able to hop on.

The cost of a ride has yet to be determined, although HART hopes to make it free, like its In-Towner downtown trolley system.

HART may face another challenge persuading people to step onto the autonomous shuttle.

"I think they need to improve the technology a little bit more before I could fully get behind driverless vehicles," said Mark Block, who lives downtown and rides the bus to his job at the Publix on Bayshore Boulevard. "It's too new; just like with anything else there's going to be bugs, and unfortunately with vehicles, bugs are going to result in injuries."

People are growing accustomed to automation in other walks of life once operated by humans, such as self-checkout aisles in retail stores and ordering screens at fast-food restaurants. For some, it's too soon to add transportation to the list.

"If I were to get on a bus and see nobody driving, that's kind of creepy," commuter Omari Carter said while waiting for a bus at the Marion Transit Center. "It's just like using the self-order thing at McDonald's. It's okay for getting food, but not for driving a bus."

On Nov. 29 and 30, Tampa's driverless shuttle will be one topic as industry leaders discuss new technology during the fourth annual Florida Automated Vehicle Summit at the Tampa Marriott Waterside Hotel. Prototypes of the shuttles will be on display.

In 2012, Florida became the second of eight states to pass legislation supporting autonomous testing and deployment. Earlier this year, that legislation was expanded to allow the vehicles on public roads.

In June, the U.S. Department of Transportation held a nationwide "Smart City challenge" to encourage ideas on how to integrate innovative technologies — self-driving cars, connected vehicles and smart sensors — into their transportation networks.

Columbus, Ohio, was awarded the challenge's $50 million prize and will become the first U.S. city to integrate a multimodal public transportation system featuring autonomous vehicles.

Morrison said HART hopes commuters will see Tampa's system as one piece among many that encourage transit use and "perhaps leaving cars at home."

The state Department of Transportation's goal is to gather data on how autonomous vehicles can redefine a transit network while providing downtown Tampa with a smoother ride up and down Marion Street.

HART hopes to get feedback on the new service as it does on all its service by capitalizing on the high use of smartphones and social media by its riders. Nearly half of them have smartphones and passenger experience is "critical for us," Eagan said.

"Florida is a very forward-thinking state," she added. "We can drive over this technology, or it can drive over us."

Contact Libby Baldwin at lbaldwin@tampabay.com.