Photograph by Frank Heuer, laif/Redux

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New York City has more than 13,000 taxicabs, and riders could be sharing many of them to cut down on traffic and pollution, according to a new study.

Photograph by Frank Heuer, laif/Redux

Taxi-Sharing Boosts Energy Efficiency, But Will Riders Get on Board?

Study argues that traffic and pollution could be cut if more travelers shared a cab.

Many of us have had the deflating experience of arriving in a city by train or plane only to encounter a line at the taxi stand that seems to last longer than the trip to get there. But how many people waiting in that queue at, say, New York City's Penn Station could be sharing cabs to the same destination?

Researchers at the Massachusetts Institute of Technology (MIT) set out to answer that question, analyzing a year's worth of New York taxi trips. They concluded that the total amount of time that taxis spent traveling could have been reduced 32 percent by shared cabs, with passengers riding no more than an extra five minutes. That reduction in travel time would result in less pollution and traffic, the researchers said, though they did not specify how much. Their work was published Tuesday in the Proceedings of the National Academy of Sciences.

Carlo Ratti, director of MIT's Senseable City Lab and one of the paper's authors, said the research is meant to quantify the benefits of taxi-sharing. "We were ourselves very surprised with the results, which are quite striking, of how much more efficiently we could use the mobility infrastructure in cities," he said.

The researchers also looked at whether such increased efficiency would be possible in other cities that have a lower density of taxis than New York. "You still find that there's a huge potential for sharing," Ratti said.

City Mobility Evolving

Ride services such as Uber and Lyft have given urban dwellers more options than ever to get around. Instead of hailing a cab, residents of cities around the world now can summon a ride via smartphone from a black SUV driven by a professional, or from a moonlighting civilian driver with a personal car out for hire. For longer trips, drivers can rent from a proliferating fleet of by-the-hour cars offered by services such as Zipcar and car2go, or from car owners who put their vehicles on sharing services. (See related: "U.S. Teenagers Are Driving Much Less: Four Theories About Why" and "Car Sharing Widens Lanes of Access for City Drivers.")

"We've seen with Airbnb that people are ready to share even intimate spaces, in their homes, now that we have systems online that allow you to know better who you're sharing with," Ratti said. Airbnb lets travelers book a stay in all or part of someone's home.

The researchers analyzed 172 million trips made by more than 13,000 taxis in New York City in 2011. On the Senseable City Lab's HubCab website, an interactive map plots all of those trips and helps illustrate the potential for sharing. Let's say you're heading from LaGuardia Airport to the corner of Park Avenue and 57th Street. Including all passenger drop-offs within a quarter-mile radius, according to the map, that same trip occurred about 6,000 times.

If even 2,000 of those trips were prevented as a result of sharing, at an average distance of nine miles from LaGuardia, and with the average vehicle emitting 368 grams of carbon per mile, nearly 7,000 kilograms of carbon emissions would be saved. That amount is roughly equivalent to the emissions from consuming 788 gallons of gas.

Will Riders Want to Share?

The researchers acknowledge, though, that there are "psychological limitations of taxi-sharing" that need to be assessed. Passengers need a clear and straightforward way to split costs, among other factors. As the researchers noted, the potential delay that sharing introduces is an important consideration. When National Geographic informally asked people on social networks whether they would share a cab with a stranger if it meant saving money, answers ranged from "Sure, why not?" to "Depends" to "Nope. I might even pay extra to not have to."

From the taxi driver's perspective, wouldn't a reduction in travel time add up to less income? The MIT researchers point to a 2013 paper from Microsoft Research and the University of Illinois that modeled a taxi-sharing scheme in Beijing. In their scenario, drivers' profit would actually increase by an average of 16 percent, while riders would save 42 percent. In that model, drivers would charge a higher fare per mile for multiple riders. Ratti also noted, "If prices go down, a new category of people might start taking taxis, hence increasing demand."

John Boit, spokesperson for the Taxicab, Limousine & Paratransit Association, noted that an experiment with cab-sharing about 20 years ago in Chicago failed because people didn't want to do it. But he said the industry isn't necessarily against the concept. "If the attitudes in America have changed and if people are more willing to do this," he said, "then obviously the industry would change with that shifting cultural idea."

Some start-ups are trying to promote that shift. Bandwagon, which makes an app that matches travelers headed in the same direction so that they can share livery cars or traditional taxis, has focused its service on high-volume hubs such as airports and conferences. It has also experimented with offering a sort of HOV lane at for taxi lines at the Consumer Electronics Show in Las Vegas, where sharers get priority access to cabs.

The customer reaction to taxi-sharing is "really context-specific," said David Mahfouda, Bandwagon's CEO. He said that when the company has run its service at a convention center for a conference, "people see the fact that they can share the ride with another passenger as a value-add. You're there for networking." At airports, too, Mahfouda said, sharing is an easier sell: "When you're traveling, you're already part of a community of travelers, and you've already spent an hour—or three hours—sharing a plane."

Uber has also embraced the idea of sharing with the trial launch this month of UberPool, which will match sharing-friendly users of the car service, potentially reducing prices for riders by 40 percent, the company said in a blog post. At the lower prices, "Uber really is cost-competitive with owning a car, which is a game-changer for consumers," it said, but warned, "there will undoubtedly be kinks and surprises to work through."

Ratti said his center's research, which is also evaluating the possible impact of self-driving cars, is focused on the question: "How are intelligent transportation systems changing the city?" The researchers plan to study the effects of taxi-sharing in other cities, including Singapore, Vienna, and Rio de Janeiro. Ratti ultimately seeks "a general law of shareability," he said, "that basically, given a city, will be able to tell you how well you could share in different neighborhoods."

In the meantime, companies such as Bandwagon and Uber are testing the concept on the ground. Bandwagon's service is primarily active in New York, Montreal, and at specific events for now, but Mahfouda said he is convinced that "dynamic social transit" will be a primary transportation mode in the future, particularly in cities.

"I think the MIT research is fantastic, but it's not a theory project," he said. "It's real. We're doing it."

The story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.