They are clearing the building room-by-room.
Shep is still not representing the escape routes well. There are multiple freeways in SB and Riverside area. Riverside is 20 minutes south on the 215. But there are also numerous police, sheriff helicopters which could be above those freeways.
The SB airport is not commercial, as he indicated finally. But Ontario is 35 minutes away and Palm Springs 40 minutes. But once the shooting starts, I would hope the EP plan would call for alerting the airports.
Regional train stations in Rancho Cucamonga and Ontario. But 30-40 minutes away.
If you want perspective, just go to your map program for San Bernardino CA and zoom in and out to see the different corridors in and out of the area.