Southwest Airlines says it is generating about $1 million a day in additional revenue from the first phases of its network connections with subsidiary AirTran Airways, in advance of the full connection that will start April 14.

The low-cost carrier has been phasing in the network connectivity, which allows for single-ticket bookings on itineraries involving both carriers. The carriers began accepting code-share bookings for five cities Jan. 26 and for 34 more on Feb. 25.

The final expansion will add the remaining 58 cities. Customers could begin booking tickets—via Southwest or AirTran—on March 18.

Southwest is not launching an advertising campaign to promote the new connections, which include some international destinations, but has been marketing the flights to targeted customers, including emails to frequent flyer members at both carriers.

Dual-branded airport kiosks went live in late February.

Southwest, which acquired AirTran in May 2011, says it is on track this year to generate $400 million in pre-tax revenue and efficiencies from the merger.

Full integration of the two carriers, with all AirTran aircraft converted to Southwest’s livery and seat configuration, is scheduled for completion by the end of 2014.