RelayRides is offering $25 in credits to drivers who try the service — a challenger to Zipcar, another Cambridge startup that offers cars by the hour. (Photo: Steven Erat)

On the way down to all those red line T cars with Zipcar ads, commuters in Porter Square first got a pitch from a competitor: RelayRides, which had a street team out Friday morning handing out cards bearing a $25 credit to try the service.

The teams already hit Harvard and Central squares. Kendall is next, and they’ll have been all through Cambridge by the end of the summer, said Boris Mordkovich, the startup’s director of marketing, in a Friday telephone interview.

“It seems to be working quite well,” Mordkovich said of the street-team process. “I can’t go into specifics, but we’re doing it again and again because it gets results.”

It was how their competitor Zipcar started its marketing efforts a decade ago, Mordkovich said, but it’s “at a different stage now.”

While Zipcar rents their own cars by the hour, RelayRides connects people who occasionally need cars with neighbors who have cars they’re not using. The carless benefit because they don’t need to buy one; car owners benefit, according to the company model, because they defray expenses, earning between $3,000 and $7,000 a year. RelayRides insures a borrowed car via a $1 million policy, company representatives say; Zipcar also takes car of such things as insurance and the cost of gas.

At least during this trial period, RelayRides is the cheaper deal by the hour. There’s no fee to join, but drivers pay at least $6 an hour, with fancier cars costing more to drive. Zipcar rates start at $7 an hour for occasional drivers, who must also pay a $25 application fee and $50 annual fee. Frequent drivers of Zipcars can go into plans with monthly fees and hourly rates starting at $6.30.

Both companies are based in Cambridge’s Kendall Square, RelayRides on Third Street and Zipcar on First. RelayRides started last year, while Zipcar launched in 2000.

Now Zipcar has more than 400,000 members in 13 major metropolitan areas and on more than 150 college campuses, as well as more than 7,000 cars, “a good number” of them hybrids. It operates in the United States, Canada and the United Kingdom, where it is partnering with a British company called Streetcar, and is in the midst of going public, spokesman John Williams said. Legally, he couldn’t discuss the initial public offering process.

But he pointed out that, in addition to those T ads, Zipcar is still very much in the community. “Community support and community involvement is a key part of what we do,” Williams said Friday, noting the company’s ongoing presence at local fairs and other events.

He said RelayRides’ presence “reinforces what Zipcar has been doing for years. Americans are rethinking their relationship with the automobile and whether they need one full time. It’s part of a growing trend toward deciding whether Americans need to own things, or just need access to them.”

The RelayRides argument is that people need access to nearby things. Founder Shelby Clark, a Harvard graduate, was a Zipcar member. He has said that the idea for RelayRides came to him when he had to walk two miles in snow to get to the nearest usable Zipcar vehicle.

Proximity is what’s behind the street teams and RelayRides’ presence at farmers markets and community fairs, Mordkovich said.

“A lot of traditional marketing activities won’t work. If we have a car in the Back Bay, it’s not really relevant to Harvard Square,” he said. “One thing we’ve been very lucky with is word of mouth. The community takes over.”

What he means is that there’s a built-in incentive for car owners to recruit renters, and for drivers to recruit car owners, since the system doesn’t work unless cars and drivers are close by and revenue is flowing. Car owners get 85 percent of what’s paid for a rental, with RelayRides taking the rest for the transaction to cover costs such as insurance and the installation of card readers so car owners and drivers never have to meet to exchange keys. (A London business called Whipcar launched April 21 with a model obliging a personal handoff of keys from owner to driver.)

Comments on a Boston Globe article about RelayRides were mixed. “I think this a fantastic idea. Sharing is the future. My car sits in my driveway all day every day, and I’d love to earn a few bucks renting it out,” one reader wrote.

“This won’t work,” another said. “Ever watch your friend drive his own car, and think to yourself, ‘Wow. He’s rough with this thing’? Constant, intense acceleration, very hard braking, sharp turns. These things wear down a car. People don’t have the same way of driving vehicles.”