RIDE-HAILING APPS such as Uber and Lyft are now the leading way passengers get to and from Logan International Airport, an indication of how rapidly their popularity is growing.

According to statistics compiled by the Massachusetts Port Authority, the ride-hailing apps have gone from handling 11 percent of pickups and dropoffs in 2016 to 21.4 percent over the course of 2017. Their momentum also seems to be building, as the apps averaged  nearly 26 percent (25.8 percent) of pickups and dropoffs during the last three months of the year.

“It’s not clear 26 percent is the cap,” said Tom Glynn, the chief executive officer of Massport, who expects the ride-hailing apps to keep growing. He noted that San Francisco International Airport, which the ride-hailing apps began serving in 2014, is now seeing as many as 34 percent of its passengers arrive or depart using them.

Glynn said Massport’s research indicates the ride-hailing apps do more dropoffs than pickups, with the split currently at 60 percent dropoff and 40 percent pickup. Massport collects a $3.25 fee from each ride-hailing driver for each pickup.

The ride-hailing apps have taken market share away primarily from limousines and taxis. The number of private dropoffs and pickups at the airport has also declined slightly, as has the number of people driving to the airport and parking. Passenger traffic on the MBTA’s Blue Line has held steady, while ridership on the Silver Line has declined slightly.

According to the Massport data, the taxi share of dropoffs and pickups has fallen from 14.2 to 10.7 percent, which is roughly the difference between 6,000 and 5,000 rides a day. The limousine share has fallen from 7.9 percent to 3.9 percent, but some of that dropoff is because Uber drivers who previously operated at Logan under livery agreements started working as regular Uber drivers when the ride-hailing apps gained full access to the airport in February 2017.

Private pickups and dropoffs at the airport fell from 21.4 percent in 2016 to 20.6 percent in 2017. The Silver Line’s share of the market fell almost half a point, dropping from 4.0 percent to 3.6 percent. And the percentage of travelers driving to the airport and parking there declined from 11.4 percent to 10.5 percent.

(The data compiled by Massport compare the year-long period from February 2016 to January 2017 to the period from February 2017 to January 2018. Ride-hailing apps gained full access to the airport in February 2017.)

In some ways, the airport is a fairly unique transportation market since travelers with bags often have different priorities than passengers going from one part of the city to another. But Glynn thinks the growth of the ride-hailing apps at Logan is indicative of what’s happening on Boston’s streets.

The impact in Boston is harder to quantify because no one is tracking the growth of the ride-hailing apps, but anecdotal evidence suggests the apps are gaining market share and contributing to congestion. MBTA officials say bus ridership is down 6 percent and subway ridership is off about 2 percent, mostly at off-peak travel periods. MBTA officials don’t have definitive proof, but they think Uber and Lyft are responsible for at least a portion of the downturn.

Just as the MBTA and state transportation officials are trying to decide how to respond to this new phenomenon, so is Glynn. Massport, for example, has obtained permission to lift the cap on parking spaces at the airport by as many as 5,000 spots, but the agency is now reviewing the data on how people get to the airport and trying to decide whether to proceed.

Glynn said there are a lot of variables to consider, including macro issues such as the economy, the growth of air travel, and the price of gasoline. He said there is also a lot of uncertainty surrounding the ride-hailing apps themselves. The apps are laying plans to eventually shift to autonomous vehicles, but the timetable for that shift is unclear. The financial underpinning of the ride-hailing apps could also shift. Uber, for example, lost nearly $4.5 billion in 2017, as the company subsidized rides in order to keep rates low and passengers coming back for more. If the ride-hailing apps raise rates to turn a profit, it’s unclear whether their growth would continue.

Glynn described the lifting of the cap on parking spaces as “an opportunity. It’s not a requirement. We’re not going to build a parking garage if we don’t need it.”

Glynn said Massport expects to make a decision about a new parking garage by the end of this year. In the meantime, the agency is moving ahead with planning for a new garage and a people-mover to take passengers getting off at the Blue Line Station at the airport to Terminal E.