This CLEO script makes the taxis on the street (both Taxi and Cabbie) randomly pick up and drop off the passengers. It does affect only a single vehicle at the same time though.

The script is directly converted from GTA LCS.

Furthermore this mod does work SAxVCxLC mod (technically it should work in GTA:Underground too, but it's untested).

In order to install the mod, just drag&drop the .cs file inside your CLEO directory.