Southwest Airlines Co. boarded more passengers in January and flew them further compared to a year ago, but its planes were less full because it increased the number of available seats.

Those were the highlights of Dallas-based Southwest’s (NYSE: LUV) preliminary traffic statistics, released today.

The carrier flew 9.4 billion revenue passenger miles in January 2017, an increase of 4.6 percent from the 8.9 billion RPMs flown in January 2016.

Available seat miles increased 6.2 percent to 12.3…