They're on a smartphone, they get texts. If there's any doubt, such as notoriously awkward or dangerous pickup spots, buildings with entrances on more than one street, or when my spidey sense says that the app has mismatched the pin and the address, I will text ahead with an appropriate query or instructions *if* I get the time at a red light. Otherwise I text my exact location upon arrival and they can guide me by phone or text as they please. I don't make calls. At 4:00 they get a second text repeating my location and stating very clearly that I will be at that location for 2 minutes and a generous six-minute total wait. That does get most of them out. Unless I'm blocking traffic, in which case I don't screw around with texts but circle the block and GTFO no-show at 5:00 sharp.