Hard to imagine anything to do with the toilet could be overflowing in the driveway!
Two things come to mind:
1. Air conditioners have a condensate drain; usually about a ¾" pipe which drips water constantly while running the A/C.
2..The other possible drain: your water heater has a temperture/pressure relief valve, located either on top or on the side. In most newer houses, and old houses if they have been upgraded, a ¾" pipe will run from this relief valve to some drain location, often just draining to an outside location as in you case.
T/P valves can just fail due to old age, or due to some debris in the water lodging in the seat. Also, a frequent cause of T/P dripping can be the pressure regulator valve on your house water supply has failed, causing your house pressure to be too high. This can be checked with a gauge which you can purchase at any harware or plumbing store for under $10.