As others have said depends on the ride.
A weekend 50 - 100 miler is usually around 16mph on the road bike
5 mile commute closer to 18mph on another roadie.
If its an mtb ride with sprog 7mph
The commute is an interesting one though, as others have said. Depending on the shift im on and time of day a car journey can be 9 -12 mph average.
I used to pay attention to average speeds but nowadays map my rides for mileage and dont worry too much about average speed, too many factors to take into account and I just enjoy riding