system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why would a city like Sydney invest in Light Rail instead of just creating dedicated bus lanes? Wouldn't the dedicated bus lanes provide greater flexibility and a lower cost?
gpt
The initial outlay for light rail is higher, but the running costs are far lower for light rail than bus services.

You need to find the balance between where to lay the tracks, and where to rely on busses.  It would not be viable to run tracks from (say) Rooty Hill to Parramatta, as the ridership would be so low.