"drive to 48" refers to the 45th Space Wing's goal of being able to support 48 launches per year from Cape Canaveral.
From the "2017 Priorities and Commitments strategic plan" (a document that outlines how the 45th Space Wing will respond to the changes in the launcher market):
Just two years ago, we anticipated Cape Canaveral Air Force Station (CCAFS) and neighboring Kennedy Space Center (which relies heavily upon us for range support) to be running at its full launch capacity in the near future, and began the process to transform the Eastern Range from its original design as a government-led space program to a new design to accommodate and support the needs of new commercial space carriers as well. And today, as a result of our commitment to our 2015 plan, we are positioning the Eastern Range and the services we provide to accommodate up to forty-eight launch operations a year.