Once every half-century or so, there is a technology that transforms transportation in America — the railroad, the automobile, or the jet plane. Some point to self-driving and electric-powered vehicles as the next breakthrough. But a 2014 study suggests that the revolution may not be new technology, but advances in how we use it.

Researchers at MIT analyzed over 150 million taxi trips in Manhattan in 2011 and found that if New Yorkers had been willing to wait five minutes more, almost all of those trips could have been shared with at least one other person. Despite the initial delay, by filling those empty seats, thousands of taxis can be taken off the road, reducing overall travel times by up to a third. Therefore, as inconvenient as this extra five-minute wait may seem at first, it will be worth it in the end to customers that need to get across the city quickly.

This would be good for taxi drivers too. They would be able to drive more or less continuously, no longer idling their engines between customers, resulting in a more predictable and stable income and saving fuel as well.

This is not a new concept. Carpooling originated during WWII to conserve rubber, and it resurfaced in the 1970’s oil crisis. Four decades later, however, the combination of white flight to the suburbs, lower gas prices, and cheaper cars have taken their toll. The 2010 census revealed that only one in ten people carpool to work, compared to one in four in the 1970’s.

Carpooling propaganda in the 1940’s. (Image credit: Wikipedia.)

But times are changing. Millennials are reversing the suburban trend and abandoning the ideal of car ownership. The emergence of a “sharing economy” after the Great Recession of 2008 has fundamentally changed our view on privacy and ownership. Nowadays we open up everything from our cars on Uber and Lyft to our homes on Airbnb to complete strangers. For some, this type of collaborative consumption is borne out of economic necessity. For others, access to the Internet and smartphones has broken down the psychological barriers that normally restricted the practice of sharing to family members, friends, and tight-knit communities.

Although data shows that ride-share services actually increased traffic in New York City by 8%, both Uber and Lyft rolled out new programs in 2014 that may change that. The MIT study concluded that an increase in shared trips significantly shortens travel times. Called UberPOOL and Lyft Line respectively, these programs now make up over half of all Uber trips and 30% of all Lyft trips. According to Uber’s internal assessment, in the first three months of 2016, UberPOOL avoided about 21 million miles of driving and about 3,800 metric tons of carbon dioxide emissions.

But, objectively, just how environmentally friendly are services like UberPOOL and Lyft Line? We may have the answer soon enough. The Transportation Sustainability Research Center at the University of California, Berkeley partnered with the National Resources Defense Council in 2015 to study the climate impact of these new transportation-network companies (TNCs). The results of their analysis are due out this fall.

In the meantime, it is safe to assume that there are competing forces at play. In New York City, with the highest share of carless households in the U.S., ride-share services such as Uber and Lyft might be luring customers from greener modes of transportation such as walking and biking, as well as taking employment opportunities away from more traditional and regulated industries such as taxi driving.

Protest against Uber by the Transportation Fairness Alliance in Portland, Oregon in January 2015. (Image credit: Wikipedia.)

Or, conversely, they might be an important complement to light rail and buses, influencing decreasing demand for individually owned vehicles, all while reducing air pollution and congestion. “What fascinates me about these things is: can they move us closer toward a vision of an integrated public transit system?” asks Dr. Susan Shaheen, who is heading up the UC Berkeley study.

So if you, like me, are a car-less 18 to 34-year-old who has taken UberPOOL, then congratulations: you have helped to shape the future of urban transportation in America. Whether that change is for better or for worse, only time will tell.