During the design phase for FIRST, the state cut back on towers in MontCo to save money, stating that they would use ISSI to make up for coverage holes. If you look at the state's tower site plan for the county, the west towards the Potomac River lacks coverage - there is only one site west of I-270, and that site is on Persimmon Tree road near the Beltway. MontCo however, is building four new sites west of I-270 more or less near the Potomac River (an area of poor coverage.) The were testing ISSI a few years ago by linking the Baltimore Simulcast cell with PG - not sure if that connection is still up.