A SPECIAL PERK and a much lower price have transformed the Massport bus operating between Back Bay and Logan International Airport into a hit with travelers.

In the first four months of its reconfigured operation, ridership more than doubled, rising from 45,864 in 2018 to 97,963 this year. On a month-by-month basis, passenger traffic has steadily increased relative to last year – up 64 percent in May, 104 percent in June, 122 percent in July, and 164 percent in August.

According to surveys of bus passengers conducted by Massport, more than half of them would have used Uber or Lyft to get to the airport if the Logan Express service was not available. That’s important, since a major goal of the spruced-up bus service is to reduce traffic to and congestion at the airport. An overhaul of ride-hailing service at the airport is coming in late October.

The key to the bus’s recent success appears to be a series of changes made in the service starting May 1. First, the price dropped from $7.50 each way ($15 roundtrip) to $3 going to the airport and free going from the airport to Back Bay ($3 roundtrip).  The new price is less than what ride-hailing apps like Uber and Lyft charge.

Riders going to the airport are also given passes that allow them to move to the front of security lines, a valuable perk at busy travel times and one that the apps can’t match.

And one of the bus pickup locations in the Back Bay moved from Copley Square to Back Bay Station, making the Logan Express bus easily accessible by subway and commuter rail. The other stop for the Logan Express bus in the Back Bay is the Hynes Convention Center on Boylston Street. Buses operate every 20 minutes from 5 a.m. to 9 p.m. starting from the Hynes and 6 a.m. to 10 p.m. starting from Logan.

Dan Gallagher, Massport’s director of aviation business and finance, said the early success of the Logan Express bus from Back Bay indicates price and convenience matter greatly to riders.

Free may be the magic word. Passenger counts on buses headed to the airport ($3 charge) increased 79 percent compared to last year, rising from 22,497 last year to 40,178 this year. By contrast, ridership from the airport to Back Bay (no charge) has gone up 147 percent, rising from 23,367 last year to 57,785 this year.

“It’s really been performing exactly as we hoped,” Gallagher said.

It’s unclear whether the MBTA could learn from the Logan Express example. Ridership on both the subway and bus system is down. Would passenger counts rise if fares were cut instead of raised? Are there perks the T or the state could offer residents to give up their cars and use public transit?

One of the biggest challenges Massport faces with the Back Bay Express Bus is getting the word out about it. Gallagher said Massport early on discovered that Google Transit didn’t even list the Back Bay Logan Express as a transportation option to the airport. Massport contacted Google and the Back Bay Express bus is now listed, but a check on Thursday indicated the website was continuing to list the price as $7.50 each way. A spokeswoman at Massport said the agency would contact Google to correct the pricing information.

Gallagher said Massport has alerted hotel concierges in the Back Bay area and trumpeted the service with ads on trash receptacles and at bus stops. But he said more work is needed to make more people aware of the service.

A majority of Logan’s passengers come from the urban core and account for the bulk of trips to and from the airport. Yet, aside from the MBTA, Massport hasn’t had a good way of serving them. The early success of the Back Bay Logan Express suggests cheap buses with perks are a good way of doing that. A similar Logan Express bus from North Station is expected to be added starting next summer and Massport also wants to increase convenience by adding e-ticketing early next year; currently, passengers pay only by credit card.