Student visa holders cannot work more than 40 hours per fortnight while their course is in session. If you are on a student visa and working as a taxi or Uber driver, then you could be breaching you visa condition if you have logged in for more than 40 hours in a fortnight. A taxi driver waiting for a fare is work in the eyes of the department even though you are not actually driving a paying passenger. The driver, although waiting for a passenger, will also be considered in the activity of taxi driving for remuneration. The bottom line is your work hours will be calculated once you log in the system irrelevant to whether you drove with a passenger for 40 hours or not.
Please refer to the following case for more detail
Case: Verma v Minister for Immigration & Anor [2017] FCCA 69 (18 January 2017)
http://www8.austlii.edu.au/cgi-bin/viewdoc/au/cases/cth/FCCA/2017/69.html